376 Sentences With "ectoderm" | Random Sentence Generator

In a SEAM, each of the four zones contains characteristics of some part of the ocular surface ectoderm, e.g.

The ectoderm produces tissues within the epidermis, aids in the formation of neurons within the brain, and constructs melanocytes. The ectoderm generates the outer layer of the embryo, and it forms from the embryo's epiblast. The ectoderm develops into the surface ectoderm, neural crest, and the neural tube. The surface ectoderm develops into: epidermis, hair, nails, lens of the eye, sebaceous glands, cornea, tooth enamel, the epithelium of the mouth and nose.

Development of the human lens begins at the 4 mm embryonic stage. Unlike the rest of the eye, which is derived mostly from the neural ectoderm, the lens is derived from the surface ectoderm. The first stage of lens differentiation takes place when the optic vesicle, which is formed from outpocketings in the neural ectoderm, comes in proximity to the surface ectoderm. The optic vesicle induces nearby surface ectoderm to form the lens placode.

During early embryonic development the ectoderm becomes specified to give rise to the epidermis (skin) and the neural plate. The conversion of undifferentiated ectoderm to neuro-ectoderm requires signals from the mesoderm. At the onset of gastrulation presumptive mesodermal cells move through the dorsal blastopore lip and form a layer in between the endoderm and the ectoderm. These mesodermal cells that migrate along the dorsal midline give rise to a structure called the notochord.

The zinc (Zn)-finger nuclear protein XFDL159, expressed in the animal cap, acts as an ectoderm factor their specifies the ectoderm by inhibiting p53 from activating genes for mesoderm differentiation.

It has inhibitory action on bone morphogenic proteins (BMPs); BMPs induce the ectoderm to become epidermal ectoderm. Inhibition of BMPs allows neuroectoderm to arise from ectoderm, a process which eventually forms the neural plate. Other inhibitors involved in this process are noggin and chordin. Follistatin and BMPs are also known to play a role in folliculogenesis within the ovary.

BMP-4 Bone morphogenetic protein 4, or BMP4, is a transforming growth factor that causes the cells of the ectoderm to differentiate into skin cells. Without BMP4 the ectoderm cells would develop into neural cells. Axial mesoderm cells under the ectoderm secrete inhibitory signals called chordin, noggin and follistatin. These inhibitory signals prevent the action of BMP4, which would normally make the cells ectoderm; as a result, the overlying cells take their normal course and develop into neural cells. The cells in the ectoderm that circumscribe these neural cells do not receive the BMP4 inhibitor signals and as a result BMP4 induces these cells to develop into skin cells.

The ectoderm consists primarily of epitheliomuscular cells, neurons, gland cells and cnidocytes.

After the definitive endoderm and intraembryonic mesoderm formations are complete, the remaining epiblast cells do not ingress through the primitive streak; rather they remain on the outside and form the ectoderm. It is not long until the ectoderm becomes the neural plate and surface ectoderm. Due to the fact that an embryo develops cranial to caudal, the formation of ectoderm does not happen at the same rate during development. The more inferior portion of the primitive streak will still have epiblast cells ingressing to make intraembryonic mesoderm, while the more superior portion has stop ingressing.

At around the third week of development, the embryo is a three-layered disc, covered with ectoderm, mesoderm and endoderm. A tube-like formation develops in the midline, called the notochord. The notochord releases extracellular molecules that affect the transformation of the overlying ectoderm into nervous tissue. The neural tube, forming from the ectoderm, contains CSF prior to the development of the choroid plexuses.

The larval form (planula) and adult form show two different body plans. The planula is a small, free-living larva, and is diploblastic with two layers: the endoderm and ectoderm with an additional mesoglea. The ectoderm thickness decreases from the anterior to posterior poles. Further, the ectoderm has mucous gland cells for secretory purposes, support, and sense along with cnidocytes with nematocysts in the posterior end.

The lens vesicle is developed from surface ectoderm. It will separate from surface ectoderm at approximately day 33. Lens capsule developed from basal lamina of lens vesicle will cover early lens fibers. Capsule is evident at 5 weeks of gestation.

Also, Rex1−/Oct3/4+ cells differentiate into cells of primitive ectoderm, the somatic cell lineage.

Elysia chlorotica gastrulation is by epiboly: the ectoderm spreads to envelope the mesoderm and endoderm.

The neural crest of the ectoderm develops into: peripheral nervous system, adrenal medulla, melanocytes, facial cartilage. The neural tube of the ectoderm develops into: brain, spinal cord, posterior pituitary, motor neurons, retina. Note: The anterior pituitary develops from the ectodermal tissue of Rathke's pouch.

Saunders and Gasseling published data in the Journal of Experimental Biology in 1948, showing that reference marks inserted near the rim of the apical border of the wing bud are dispersed throughout the whole forearm of the wing. This led them to believe that the apical ectoderm may play a role in forming parts of the wing. To test this, they removed apical ectoderm from wing buds which yielded deformed wings. When they removed dorsal ectoderm, normal wings formed.

Ectoderm-neural cortex protein 2 is a protein that in humans is encoded by the KLHL25 gene.

Ectoderm-neural cortex protein 1 is a protein that in humans is encoded by the ENC1 gene.

To make an organoid, an embryoid (tissue that has some embryonic features) grown from natural stem cells is used. Embryos have three layers: endoderm, mesoderm and ectoderm. Each turns into various body parts. The nervous system grows from the ectoderm (which also contributes dental enamel and the epidermis).

EDAR and other genes provide instructions for making proteins that work together during embryonic development. These proteins form part of a signaling pathway that is critical for the interaction between two cell layers, the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the proper formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.

This is a list of cells in humans derived from the three embryonic germ layers – ectoderm, mesoderm, and endoderm.

Currently there is no identified cause of acalvaria. The primary presumed pathogenesis is problematic migration of the membranous neurocranium with respect to the normal positioning of the immature ectoderm. When an embryo develops normally, the anterior neural pore closes about the fourth week. After this occurs, mesenchymal tissue migrates under the ectoderm.

Due to the pluripotency of P19 cells, those new derived cell lines can be ectoderm, mesoderm and endoderm-like cells.

Xema, a foxi-class gene expressed in the gastrula stage Xenopus ectoderm, is required for the suppression of mesendoderm. Development 132, 2733-2742. A new factor specific for the ectoderm, XFDL156, has shown to be essential for suppression of mesoderm differentiation from pluripotent cells.Sasai, N., Yakura, R., Kamiya, D., Nakazawa, Y., and Sasai, Y. (2008).

Anatomy of a coral polyp The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of cells. The outer layer is known technically as the ectoderm, the inner layer as the endoderm (or gastroderm). Between ectoderm and endoderm is a supporting layer of structureless gelatinous substance termed mesoglea, secreted by the cell layers of the body wall. The mesoglea can be thinner than the endoderm or ectoderm or comprise the bulk of the body as in larger jellyfish.

In amniote animal embryology, the epiblast (also known as the primitive ectoderm) is one of two distinct layers arising from the inner cell mass in the mammalian blastocyst or from the blastodisc in reptiles and birds. It derives the embryo proper through its differentiation into the three primary germ layers, ectoderm, mesoderm and endoderm, during gastrulation. The amnionic ectoderm and extraembryonic mesoderm also originate from the epiblast. The other layer of the inner cell mass, the hypoblast, gives rise to the yolk sac, which in turn gives rise to the chorion.

The mesoderm layer is established next as migrating epiblast cells move through the primitive streak then spread out within the space between the endoderm and remaining epiblast, which once the mesoderm layer has formed ultimately becomes the definitive ectoderm. The process of gastrulation results in a trilaminar germ disc, consisting of the ectoderm, mesoderm and endoderm layers.

Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous.

Although proneural genes operate in the ectoderm, lethal of scute acts in the somatic mesoderm to define cell cluster from which muscle progenitors will be single out. The interaction between these cells and ectoderm, leads to the formation of muscle founder cells, in an analogous process to the one that occurs in the central nervous system.

Hanley says that when embryos merge at an early stage, what happens is that one of them becomes the ectoderm, one the endoderm, and the mesoderm is up for grabs. In rare cases, an embryo may split laterally with all 3 layers. This was found in a bird, for instance. The nervous system forms from a fold in ectoderm.

Therefore, it is unlikely that epithelial tissue would become trapped as there is no ectoderm separating the lobes in the first instance.

Because of its great importance, the neural crest is sometimes considered a fourth germ layer. It is, however, derived from the ectoderm.

The stomodeum is lined by ectoderm, and is separated from the anterior end of the fore-gut by the buccopharyngeal membrane. This membrane is devoid of mesoderm, being formed by the apposition of the stomodeal ectoderm with the fore-gut endoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future pharynx.

Embryological mesenchyme is particularly transitory and soon differentiates after migration. Neural mesenchyme forms soon after primary mesenchyme formation. The interaction with ectoderm and somite-forming morphogenic factors cause some primary mesenchyme to form neural mesenchyme, or paraxial mesoderm, and contribute to somite formation. Neural mesenchyme soon undergoes a mesenchymal–epithelial transition under the influence of WNT6 produced by ectoderm to form somites.

Cells that remain in the epiblast become ectoderm. This is the trilaminar disc and the epiblast cells have given rise to the three germ layers.

The Lens placode is a thickened portion of ectoderm which serves as the precursor to the lens. SOX2 and Pou2f1 are involved in its development.

The upper part of the anal canal is derived from endoderm of the hindgut. The lower part (one-third) is derived from ectoderm around the proctodeum. Ectoderm, in the region of the proctodeum on the surface of part of the cloaca, proliferates and invaginates to create the anal pit. Subsequently, degeneration of the cloacal membrane establishes continuity between the upper and lower parts of the anal canal.

"Embryonic and Postnatal Development of the Eye". Retrieved 22 April 2015. During the invagination of the optic cup, the ectoderm begins to thicken and form the lens placode, which eventually separates from the ectoderm to form the lens vesicle at the open end of the optic cup. Further differentiation and mechanical rearrangement of cells in and around the optic cup gives rise to the fully developed eye.

Following this, a narrow line of cells appears on the surface on the embryo. Its growth makes the embryo undergo gastrulation, in which the three primary tissue layers of the fetus, the ectoderm, mesoderm, and endoderm, develop. The narrow line of cells begin to form the endoderm and mesoderm. The ectoderm begins to grow rapidly as a result of chemicals being produced by the mesoderm.

At the 4 mm stage, the lens placode is a single monolayer of columnar cells. As development progresses, the lens placode begins to deepen and invaginate. As the placode continues to deepen, the opening to the surface ectoderm constricts and the lens cells forms a structure known as the lens vesicle. By the 10 mm stage, the lens vesicle has completely separated from the surface ectoderm.

These neural crest cells migrate from the ectoderm as the forebrain closes, invading the space that will form the frontonasal prominence. The maxillary and mandibular prominences are derived from the first arch. The maxillary prominence is initially located superior/lateral to the stomodeum while the mandibular prominence is located inferior to it and will fuse early on. Nasal placodes originate on the frontonasal prominence from the ectoderm.

The Xenopus laevis anterior gradient genes - XAG-1, XAG-2, and XAG-3 - were discovered through dissection of different-aged embryos. They become expressed in the anterior region of the dorsal ectoderm in late gastrula embryos. XAG-2 expression gathers at the anterior region of the dorsal ectoderm, and this region corresponds to the cement gland anlage. Many other homologous proteins have been discovered afterwards in Xenopus.

Ectodermal cells overlying the notochord develop into the neural plate in response to a diffusible signal produced by the notochord. The remainder of the ectoderm gives rise to the epidermis (skin). The ability of the mesoderm to convert the overlying ectoderm into neural tissue is called neural induction. The neural plate folds outwards during the third week of gestation to form the neural groove.

This can happen because the cranial neuropore is still open, which is responsible for the ultimate fusion and formation of the brain stem and central nervous system. Furthermore, this secondary fusion of embryonic discs could implicate that intact skin will not fuse to other intact skin, including the ectoderm of the embryo. This means that two embryonic discs could only unite in locations where the ectoderm is absent. Moreover, the fusion occurs from neural folds of two separate, dorsally oriented embryonic discs, and the union can occur only after the ectoderm is disrupted to allow the neural and surface ectodermal layers to separate from each other.

If the development of the iris is hindered, the ectoderm of the eye (which forms the lens and corneal epithelium) may split, which could lead to pseudopolycoria.

Dev Biol 315, 161-172. FoxI1e is dependent on BMP signals in the neurula stage, limiting the localization of FoxI1e to the ventral side of the ectoderm.

The funnel of cephalopods develops on the top of their head, whereas the mouth develops on the opposite surface. The early embryological stages are reminiscent of ancestral gastropods and extant Monoplacophora. The shells develop from the ectoderm as an organic framework which is subsequently mineralized. In Sepia, which has an internal shell, the ectoderm forms an invagination whose pore is sealed off before this organic framework is deposited.

The limb bud is a structure formed early in vertebrate limb development. As a result of interactions between the ectoderm and underlying mesoderm, formation occurs roughly around the fourth week of development. In the development of the human embryo the upper limb bud appears in the third week and the lower limb bud appears four days later. The limb bud consists of undifferentiated mesoderm cells that are sheathed in ectoderm.

Such imprinted genes are required for the formation of the placenta as well as the development of cellular lineages such as those derived from the mesoderm and ectoderm.

Exomphalos is caused by a failure of the ventral body wall to form and close the naturally occurring umbilical hernia that occurs during embryonic folding which is a process of embryogenesis. The normal process of embryogenesis is that at 2 weeks gestation the human embryo is a flat disc that consists of three layers, the outer ectoderm and inner endoderm separated by a middle layer called the mesoderm. The ectoderm gives rise to skin and the CNS, the mesoderm gives rise to muscle and the endoderm gives rise to organs. The focus areas for exomphalos are that the ectoderm will form the umbilical ring, the mesoderm will form the abdominal muscles and the endoderm will form the gut.

The primitive streak is produced by a thickening of the axial part of the ectoderm, the cells of which multiply, grow downward, and blend with those of the subjacent endoderm. From the sides of the primitive streak a third layer of cells, the mesoderm, extends laterally between the ectoderm and endoderm; the caudal end of the primitive streak forms the cloacal membrane. The blastoderm now consists of three layers, an outer ectoderm, a middle mesoderm, and an inner endoderm; each has distinctive characteristics and gives rise to certain tissues of the body. For many mammals, it is sometime during formation of the germ layers that implantation of the embryo in the uterus of the mother occurs.

During development, definitive endoderm and ectoderm differentiates into several gastrointestinal epithelial lineages, including endocrine cells. Many studies have indicated that Notch signaling has a major role in endocrine development.

The zone of polarizing activity (ZPA) is an area of mesenchyme that contains signals which instruct the developing limb bud to form along the anterior/posterior axis. Limb bud is undifferentiated mesenchyme enclosed by an ectoderm covering. Eventually, the limb bud develops into bones, tendons, muscles and joints. Limb bud development relies not only on the ZPA, but also many different genes, signals, and a unique region of ectoderm called the apical ectodermal ridge (AER).

According to Liem et al., the organogenesis of the eye is pointed out as an example of a developmental cascade of inductions. The eye is essentially a derivative of the ectoderm from the somatic ectoderm and neural tube, with a succession of inductions by the chordamesoderm. Chordamesoderm induces the anterior portion of the neural tube to form the precursors of the synapomorphic tripartite brain of vertebrates, and it will form a bulge called the diencephalon.

The otic placode visible on this sketch of a developing embryo. After implantation, around the second to third week the developing embryo consists of three layers: endoderm, mesoderm and ectoderm. The first part of the ear to develop is the inner ear, which begins to form from the ectoderm around the 22nd day of the embryo's development. Specifically, the inner ear derives from two thickenings called otic placodes on either side of the head.

Mesoderm cells condense to form a rod which will send out signals to redirect the ectoderm cells above. This fold along the neural tube sets up the vertebrate central nervous system.

BMP antagonists diffusing from the ectoderm generates a gradient of BMP activity. In this manner, the neural crest lineage forms from intermediate levels of BMP signaling required for the development of the neural plate (low BMP) and epidermis (high BMP). Fgf from the paraxial mesoderm has been suggested as a source of neural crest inductive signal. Researchers have demonstrated that the expression of dominate-negative Fgf receptor in ectoderm explants blocks neural crest induction when recombined with paraxial mesoderm.

Secreted proteins such as BMP and its antagonist Noggin and chordin act permissively to establish the fate of neural tissue in the dorsal ectoderm and enables the formation of the neural plate.

150 Years of cell division. Dermatopathology: Practical & Conceptual, Vol. 8, No. 2. link. The term "mesoderm" was introduced into English by Huxley in 1871, and "ectoderm" and "endoderm" by Lankester in 1873.

During embryogenesis the ear develops as three distinct structures: the inner ear, the middle ear and the outer ear. Each structure originates from a different germ layer: the ectoderm, endoderm and mesenchyme.

Specification of endoderm depends on rearrangement of maternally deposited determinants, leading to nuclearization of Beta-catenin. Mesoderm is induced by signaling from the presumptive endoderm to cells that would otherwise become ectoderm.

During the development of morphological features while in the embryo, or embryogenesis, a cluster of cells grow underneath the ectoderm which later in development, after the lateral ectoderm has grown dorsally to form wind imaginal disc. An example of wing bud development in the larvae, can be seen in those of White butterflies (Pieris). In the second instar the histoblast become more prominent, which now form a pocket-like structure. As of the third and fourth instars, the histoblast become more elongated.

Nautiluses are the only extant cephalopods with a true external shell. However, all molluscan shells are formed from the ectoderm (outer layer of the embryo); in cuttlefish (Sepia spp.), for example, an invagination of the ectoderm forms during the embryonic period, resulting in a shell (cuttlebone) that is internal in the adult. The same is true of the chitinous gladius of squid and octopuses. Cirrate octopods have arch-shaped cartilaginous fin supports, which are sometimes referred to as a "shell vestige" or "gladius".

Developmental neurogenesis of nerve nets is conserved between phyla and has been mainly studied in cnidaria, especially in the model organism Hydra. The following discusses the development of the nerve net in Cnidaria, but the same mechanism for the differentiation of nervous tissue is seen in Ctenophora and Echinodermata. Cnidaria develop from two layers of tissue, the ectoderm and the endoderm, and are thus termed diploblasts. The ectoderm and the endoderm are separated by an extra-cellular matrix layer called the mesoglea.

Cnidaria begin to differentiate their nervous systems in the late gastrula. In Hydrozoa and Anthozoa, interstitial stem cells from the endoderm generate neuroblasts and nematoblasts which migrate to the ectoderm and provide for the formation of the nervous system along the anterior-posterior axis. Non-hydrozoa lack interstitial stem cells, and the neurons arise from epithelial cells, which are most likely differentiated from the ectoderm as occurs in vertebrates. Differentiation occurs near the aboral pore and this is where most neurons remain.

At the same time, Wnt-7a is expressed in the dorsal ectoderm, and provides further positive feedback to FGF-4 and Shh. Without this system, limbs and digits are either significantly reduced or missing.

EEM syndrome (or Ectodermal dysplasia, Ectrodactyly and Macular dystrophy syndrome) is an autosomal recessive congenital malformation disorder affecting tissues associated with the ectoderm (skin, hair, nails, teeth), and also the hands, feet and eyes.

The inner wall will be called the archenteron; the primitive gut. The archenteron will open to the exterior through the blastopore. The outer wall will become the ectoderm. Later forming the epidermis and neural crest.

In arthropods, the integument, or external "skin", consists of a single layer of epithelial ectoderm from which arises the cuticle, an outer covering of chitin, the rigidity of which varies as per its chemical composition.

The cloaca is, for a time, shut off from the anterior by the cloacal membrane, formed by the apposition of the ectoderm and endoderm, and reaching, at first, as far forward as the future umbilicus. Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and pubic symphysis. By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca.

Their oral disk also has small grains embedded inside of it, leading to an appearance of silvery flecks on the ectoderm of the organism. Due to the presence of photosynthetic zooxanthellae, they have a brown coloration.

In the anatomy of an embryo, the somatopleure is a structure created during embryogenesis when the lateral mesoderm splits into two layers. The outer (or somatic) layer becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure. The combination of ectoderm and mesoderm, or somatopleure, forms the amnion, the chorion and the lateral body wall of the embryo. The limbs are formed from the somatic mesoderm cells are induced by hox genes and the expression of other molecules to suffer and epithelial- mesenchyme transition.

The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the 4th week of pregnancy. Optic vesicles are outgrowings of the brain which make contact with the surface ectoderm and this contact induces changes necessary for further development of the eye. Through a groove at the bottom of the optic vesicle known as choroid fissure the blood vessels enter the eye. Several layers such as the neural tube, neural crest, surface ectoderm, and mesoderm contribute to the development of the eye.

Further induction by the chordamesoderm will form a protrusion: the optic vesicle. This vesicle will be subsequently invaginated by means of further inductions from the chordamesoderm. The optic vesicle will then induce the ectoderm that thickens (lens placode) and further invaginates to a point that detaches from the ectoderm and forms a neurogenic placode by itself. The lens placode is affected by the chordamesoderm making it to invaginate and forms the optic cup composed by an inner layer of neural retina and outer layer the pigmented retina that will unite and form the optic stalk.

Mammalian PGCs are specified by signalling between cells (induction), rather than by the segregation of germ plasm as the embryo divides. In mice, PGCs originate from the proximal epiblast, close to the extra-embryonic ectoderm (ExE), of the post-implantation embryo as early as embryonic day 6.5. By E7.5 a founding population of approximately 40 PGCs are generated in this region of the epiblast in the developing mouse embryo. The epiblast, however, also give rise to somatic cell lineages that make up the embryo proper; including the endoderm, ectoderm and mesoderm.

Between ectoderm and endoderm is a supporting layer of gelatinous substance termed mesoglea, secreted by the cell layers of the body wall. The mesoglea can contain skeletal elements derived from cells migrated from ectoderm. The sac-like body built up in this way is attached to a hard surface, which in hard corals are cup-shaped depressions in the skeleton known as corallites. At the center of the upper end of the sac lies the only opening called the mouth, surrounded by a circle of tentacles which resemble glove fingers.

All of the different cells of an animal are derived from the embryonic germ layers. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic. All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the ectoderm, mesoderm and endoderm. Animal tissues can be grouped into four basic types: connective, epithelial, muscle and nervous tissue.

The Central Nervous System (CNS) and memory in the fetus develop from the ectoderm following fertilization via a process called neurulation. The ectoderm is the outermost layer of the embryo. This happens towards the end of the third week of gestation (time period when the embryo is carried in the women's uterus) and ends with the start of the development of the neural tube, an important structure crucial to development of the central nervous system. Some evidence suggests memory is actually responsible for carrying out the development of the CNS during neurulation.

By the end of the fourth week of gestation, the open ends of the neural tube, called the neuropores, close off. A transplanted blastopore lip can convert ectoderm into neural tissue and is said to have an inductive effect. Neural inducers are molecules that can induce the expression of neural genes in ectoderm explants without inducing mesodermal genes as well. Neural induction is often studied in xenopus embryos since they have a simple body pattern and there are good markers to distinguish between neural and non- neural tissue.

Neural plate Neural tube development Following gastrulation, the ectoderm gives rise to epithelial and neural tissue, and the gastrula is now referred to as the neurula. The neural plate that has formed as a thickened plate from the ectoderm, continues to broaden and its ends start to fold upwards as neural folds. Neurulation refers to this folding process whereby the neural plate is transformed into the neural tube, and this takes place during the fourth week. They fold, along a shallow neural groove which has formed as a dividing median line in the neural plate.

A melanoblast is a precursor cell of a melanocyte. These cells migrate from the trunk neural crest cells (in terms of axial level from neck to posterior end) dorsolaterally between the ectoderm and dorsal surface of the somites.

Once the endoderm cells were invaginated, the cells will keep moving beneath the ectoderm. Later, the blastopore will be formed and with this, the invagination process is complete. The blastopore will be surrounded by the mesoderm by all sides.

Silicon is present throughout the life, but decreases with age, as does the number of spherites. The hindgut is a short invagination of the ectoderm, linking the midgut to the anus. It can be dilated and shortened by muscles.

Mir, A., Kofron, M., Zorn, A.M., Bajzer, M., Haque, M., Heasman, J., and Wylie, C.C. (2007). FoxI1e activates ectoderm formation and controls cell position in the Xenopus blastula. Development 134, 779-788.Suri, C., Haremaki, T., and Weinstein, D.C. (2005).

Siegel, P.M., and Massague, J. (2003). Cytostatic and apoptotic actions of TGFβeta in homeostasis and cancer. Nature Reviews – Cancer 3, 807-821. During ectoderm specification, the function of Smad4 is regulated by ubiquitination and deubiquitination made by ectodermin and FAM, respectively.

Meanwhile, the lateral nasal prominence gives rise to the alae of the nose and fuses with the maxillary prominence, forming the Nasolacrimal duct. This duct is formed when the ectoderm thickens into a cord and sinks into the underlying mesenchyme.

The embryionic somatopleure is then divided into 3 sections, the anterior limb bud formation, the posterior limb bud formation and the non limb forming wall. The bud forming sections grow in size at the somatic mesoderm under the ectoderm proliferate in mesenchyme form. In chicken, the extraembryonic tissues are separated into two layers: the splanchnopleure composed of the endoderm and splanchnic mesoderm, and the somatopleure composed of the ectoderm and somatic mesoderm along with the formation of the coelomic cavity after gastrulation. The amnion and chorion are derived from the somatopleure with a presumptive border of the ectamnion.

As such, the neural crest - in Hall's view - plays a role equivalent to that of the endoderm, mesoderm, and ectoderm of bilaterian development and is a definitive feature of vertebrates (as hypothesized by Gans and Northcutt[1983]). As such, vertebrates are the only quadroblastic, rather than triploblastic bilaterian animals. In vertebrates the neural crest serves to integrate the somatic division (derived from ectoderm and mesoderm) and visceral division (derived from endoderm and mesoderm) together via a wide range novel vertebrate tissues (bone, cartilage, sympathetic nervous system, etc...). He has been associated with Dalhousie University since 1968.

Embryonic stem cells of the inner cell mass are pluripotent, meaning they are able to differentiate to generate primitive ectoderm, which ultimately differentiates during gastrulation into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. These germ layers generate each of the more than 220 cell types in the adult human body. When provided with the appropriate signals, ESCs initially form precursor cells that in subsequently differentiate into the desired cell types. Pluripotency distinguishes embryonic stem cells from adult stem cells, which are multipotent and can only produce a limited number of cell types.

Once blastoderm cells have covered almost half of the yolk cell, thickening throughout the margin of deep cells occurs. The thickening is referred to as the germ ring and is made up of a superficial layer, the epiblast which will become ectoderm, and an inner layer called the hypoblast which will become endoderm and mesoderm. As the blastoderm cells undergo epiboly around the yolk the internalization of cells at the blastoderm margin start to form hypoblast. Presumptive ectoderm or epiblast cells do not internalize but the deep cells (inner layer of cells) do and they become the mesoderm and endoderm.

The germ line segregates from the somatic cells through the formation of pole cells at the posterior end of the embryo. After thirteen mitotic divisions and about 4 hours after fertilization, an estimated 6,000 nuclei accumulate in the unseparated cytoplasm of the oocyte before they migrate to the surface and are encompassed by plasma membranes to form cells surrounding the yolk sac producing a cellular blastoderm. Like other triploblastic metazoa, gastrulation leads to the formation of three germ layers: the endoderm, mesoderm, and ectoderm. The mesoderm invaginates from the ventral furrow (VF), as does the ectoderm that will give rise to the midgut.

The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck. They consist of three layers, the ectoderm, mesoderm and endoderm, which form the mesenchyme (derived form the lateral plate mesoderm and paraxial mesoderm), neural crest and neural placodes (from the ectoderm). The paraxial mesoderm forms structures named somites and somitomeres that contribute to the development of the floor of the brain and voluntary muscles of the craniofacial region. The lateral plate mesoderm consists of the laryngeal cartilages (arytenoid and cricoid).

In Xenopus laevis, the specification of the three germ layers (endoderm, mesoderm and ectoderm) occurs at the blastula stage.Heasman, J., Quarmby, J., and Wylie, C.C. (1984). The mitochondrial cloud of Xenopus oocytes: the source of germinal granule material. Dev Biol 105, 458-469.

The nasal placode (or olfactory placode) gives rise to the olfactory epithelium of the nose. Two nasal placodes arise as thickened ectoderm from the frontonasal process. They give rise to the nose, the philtrum of the upper lip, and the primary palate.

In primary neurulation, the layer of ectoderm divides into three sets of cells: the neural tube (future brain and spinal cord), epidermis (skin), and neural crest cells (connects epidermis and neural tube and will migrate to make neurons, glia, and skin cell pigmentation).

The chorion and amnion are composed of extraembryonic ectoderm and mesoderm, where as the yolk sac is made of extraembryonic endoderm and mesoderm. When day 13 rolls around, the connecting stalk, a dense portion of extraembryonic mesoderm, restrains the embryonic disc in the chorionic cavity.

Koller's sickle induces primitive streak and Hensen's node, which are major components of avian gastrulation. Avian gastrulation is a process by which developing cells in an avian embryo move relative to one another in order to form the three germ layers (endoderm, mesoderm, and ectoderm).

The development of the nervous system in radiata is relatively unstructured. Unlike bilaterians, radiata only have two primordial cell layers, endoderm and ectoderm. Neurons are generated from a special set of ectodermal precursor cells, which also serve as precursors for every other ectodermal cell type.

When abd-A is ectopically expressed throughout the embryo, all segments anterior of A4 are transformed to an A4-like abdominal identity. The abd-A gene also affects the pattern of cuticle generation in the ectoderm, and pattern of muscle generation in the mesoderm.

Meanwhile, the ectoderm and endoderm continue to curve around and fuse to create the body cavity, completing the transformation of the embryo from a flattened disk to a three–dimensional body. Cells originating from the fused tips of the neuroectoderm (neural crest cells) migrate to various locations throughout the embryo, where they will initiate the development of diverse body structures (D). The formation of the neural fold is initiated by the release of calcium from within the cells. The released calcium interacts with proteins that can modify the actin filaments in the outer epithelial tissue, or ectoderm, in order to induce the dynamic cell movements necessary to create the fold.

BMP-4 signals ectoderm cells to develop into skin cells, but the secretion of inhibitors by the underlying mesoderm blocks the action of BMP-4 to allow the ectoderm to continue on its normal course of neural cell development. Additionally, secretion of BMPs by the roof plate in the developing spinal cord helps to specify dorsal sensory interneurons. As a member of the transforming growth factor-beta superfamily, BMP signaling regulates a variety of embryonic patterning during fetal and embryonic development. For example, BMP signaling controls the early formation of the Mullerian duct (MD) which is a tubular structure in early embryonic developmental stage and eventually becomes female reproductive tracts.

Dullard is a member of DXDX(T/V) phosphatase family. It was shown in 2002 to be a potential regulator of neural tube development in Xenopus. Neural development happens in the dorsal ectoderm. In the genus Xenopus, over expression of Dullard undergoes apoptosis in early development.

Most animals are bilaterians, excluding sponges, ctenophores, placozoans and cnidarians. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Except for a few phyla (i.e. flatworms and gnathostomulids), bilaterians have complete digestive tracts with a separate mouth and anus.

During early in development in Xenopus, the transcription factor FoxI1e/Xema activates epidermal differentiation and represses endoderm and mesoderm specific genes in animal caps (Suri et al., 2005). It is suggested that FoxI1e is active before the ectoderm differentiates into epidermis and the central nervous system.

Gastrulation of a diploblast: The formation of germ layers from a (1) blastula to a (2) gastrula. Some of the ectoderm cells (orange) move inward forming the endoderm (red). Among animals, sponges show the simplest organization, having a single germ layer. Although they have differentiated cells (e.g.

By the end stage 6, the zygote contains a set of 25 micromeres, 3 macromeres (A, B and C) and 10 teloblasts derived from the D quadrant. The teloblasts are pairs of five different types (M, N, O, P, and Q) of embryonic stem cells that form segmented columns of cells (germinal band) in the surface of the embryo. The M-derived cells make mesoderm and some small set of neurons, N results in neural tissues and some ventral ectoderm, Q contributes to the dorsal ectoderm and O and P in the leech are equipotent cells (same developmental potential) that produce lateral ectoderm; however the difference between the two of them is that P creates bigger batches of dorsolateral epidermis than O. The sludgeworm Tubifex, unlike the leech, specifies the O and P lineages early in development and therefore, these two cells are not equipotent. Each segment of the body of the leech is generated from one M, O, P cell types and two N and two Q cells types.

Transactions of the American Philosophical Society. 44, Issue 2, 139–317. He is best known for reducing Karl Ernst von Baer's four germ layers to three: the ectoderm, mesoderm, and endoderm. He also discovered unmyelinated nerve fibres and the nerve cells in the heart sometimes called Remak's ganglia.

It has also been found that the msp130 gene exhibits a complex pattern of spatial regulation within the PMC syncytium during skeletogenesis. It is suggested that the ectoderm may play a role in controlling skeletal morphogenesis by regulating the expression of PMC- specific gene products involved in spicule biogenesis.

There is initially a cloacal membrane, composed of ectoderm and endoderm, reaching from the umbilical cord to the tail, separating the cloaca from the exterior. After the separation of the rectum from the dorsal part of the cloaca, the ventral part of the cloacal membrane becomes the urogenital membrane.

Within the latter type, hairs in structures called pilosebaceous units have a hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands are from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

At about 22 days into development, the ectoderm on each side of the rhombencephalon thickens to form otic placodes. These placodes invaginate to form otic pits, and then otic vesicles. The otic vesicles then form ventral and dorsal components. The ventral component forms the saccule and the cochlear duct.

Neurulation and neural crest cells vesicle stages of development in the early embryo to the fifth week Brain of a human embryo in the sixth week of development At the beginning of the third week of development, the embryonic ectoderm forms a thickened strip called the neural plate. By the fourth week of development the neural plate has widened to give a broad cephalic end, a less broad middle part and a narrow caudal end. These swellings are known as the primary brain vesicles and represent the beginnings of the forebrain, midbrain and hindbrain. Neural crest cells (derived from the ectoderm) populate the lateral edges of the plate at the neural folds.

Morphologically, the AER emerges as a thickening of the ectoderm at the distal rim of the limb bud. This distinct structure runs along the anterior-posterior axis of the limb bud and subsequently separates the dorsal side of the limb from its ventral side. In the wing bud in chick embryos, the AER becomes anatomically distinguishable at the late stage of development 18HH (corresponding to 3 day-old embryos), when the distal ectodermal cells of the bud acquire a columnar shape distinguishing them from the cuboidal ectoderm. At stage 20HH (corresponding to 3.5 day-old embryos), the AER appears as a strip of pseudostratified epithelium which is maintained until 23-24HH (corresponding to 4-4.5 day-old embryos).

Afterwards, the AER progressively decreases in height and eventually regresses. In mouse embryos, the ventral ectoderm of the emerging forelimb at E9.5 (embryonic day 9.5) already appears thicker in comparison to the dorsal ectoderm and it corresponds to the early AER. By E10, this thickening is more noticeable since the epithelium now consists of two layers and becomes confined to the ventral- distal margin of the bud although it is not detectable in living specimens using light microscope or by scanning electron microscopy (SEM). Between E10.5-11, a linear and compact AER with a polystratified epithelial structure (3-4 layers) has formed and positioned itself at the distal dorso-ventral boundary of the bud.

Mice and other mammalian species undergo epigenesis during development, where germ cells are separated from the somatic lineage during early gastrulation, occurring at embryonic day 7 in mice, and are derived directly from proximal epiblast cells relative to the extraembryonic ectoderm. Prior to gastrulation the epiblast cells are not yet set in their role as cells of the germ lineage and can act as precursors for somatic cells Matsui and Okamura, 2003. At this stage, cells transplanted to the proximal epiblast from other parts of the epiblast can also be differentiated into germ line cells. The potential germ line cells are specified by the extracellular signalling of BMP4, BMP2 and BMP8b from the extraembryonic ectoderm.

Enamel is the hardest and most highly mineralized substance of the body. It has its origin from oral ectoderm. It is one of the four major tissues which make up the tooth, along with dentin, cementum, and dental pulp. It is normally visible and must be supported by underlying dentin.

Harvestman eating a skink tail The foregut (stomodeum) develops from the ectoderm. It is called pharynx before passing through the central nervous system, and esophagus inside the CNS. Shortly afterwards it empties into the midgut. The midgut (mesenteron) is the largest organ in harvestmen and fills most of the opisthosoma.

Mir et al., 2005 identified FoxI1e (Xema) by selecting genes that were down-regulated under mesoderm-inducing signals in the ectoderm compared to vegetal region of an early blastula embryo. Also, high expression of this gene was observed in animal caps in embryos that lack VegT compared to wild type.

During development, the blastula forms three tissue layers: the ectoderm, mesoderm, and endoderm. The mesoderm tissue produces the coelum, which gives rise to the body cavity and specialized tissues and organs. Fertilized eggs hatch into larvae. These undergo four zoeal stages, followed by a megalopal stage, and finally an adult stage.

During development, somatic cells will become more specialized and form the three primary germ layers: ectoderm, mesoderm, and endoderm. After formation of the three germ layers, cells will continue to specialize until they reach a terminally differentiated state that is much more resistant to changes in cell type than its progenitors.

Mutations in the Polycomb-group (PcG) complexes also presented significant modifications in physiological systems of organisms. Hence, modification in silencer elements and sequences can result in either devastating or unnoticeable changes. Proper neural folding. Specialized cells called the notochord (A) induces ectoderm above it to become the primitive nervous system.

This layer is highly vascularized and rich in stromal components. The third is the allantoic epithelium that consists of epithelial cells arising from the allantoic ectoderm. It forms a part of the wall of the allantoic sac. Both the epithelial layers are separated from the mesodermal layer by basement membranes.

The two layers cover the intraembryonic cavity. The parietal layer together with overlying ectoderm forms the lateral body wall folds. The visceral layer forms the walls of the gut tube. Mesoderm cells of the parietal layer form the mesothelial membranes or serous membranes which line the peritoneal, pleural and pericardial cavities.

Polyp prey includes copepods and fish larvae.Chang, T.D. and Sullivan, J.M. "Temporal associations of coral and zooplankton activity on a Caribbean reef " Dartmouth Studies in Tropical Ecology. 2008. Accessed 2009-06-21. Longitudinal muscular fibrils formed from the cells of the ectoderm allow tentacles to contract when conveying the food to the mouth.

In the case of wound healing, myoepithelial cells reactively proliferate. Presence of myoepithelial cells in a hyperplastic tissue proves the benignity of the gland and, when absent, indicates cancer. Only rare cancers like adenoid cystic carcinomas contains myoepithelial cells as one of the malignant component. It can be found in endoderm or ectoderm.

Vendoglossa is a fossil from the Nama Group of Namibia from the Precambrian period. It is also known as the "cat's tongue organism". The type species is Vendoglossa tuberculata. The fossil has been interpreted as a dorso-ventrally compressed stem-group metazoan, with a large gut cavity and a transversely ridged ectoderm.

The plexus is the characteristic form of nervous system in the coelenterates and persists with modifications in the flatworms. The nerves of the radially symmetric echinoderms also take this form, where a plexus underlies the ectoderm of these animals and deeper in the body other nerve cells form plexuses of limited extent.

The contact between these remnants and pharyngeal ectoderm leads to the growth of respiratory epithelium. This forms Tornwaldt's bursa which drains into the nasopharyngeal cavity. This only forms cyst when the orifice partially or completely obstructed by infection. A Tornwaldt's cyst progresses in to Tornwaldt's disease only after infection or inflammation occurs.

DLX5 begins to express DLX5 protein in the facial and branchial arch mesenchyme, otic vesicles, and frontonasal ectoderm at around day 8.5-9. By day 12.5, DLX5 protein begins to be expressed in the brain, bones, and all remaining skeletal structures. Expression in the brain and skeleton begins to decrease by day 17.

At the end of the third week, the neural tube, which is a fold of one of the layers of the trilaminar germ disc, called the ectoderm, appears. This layer elevates and closes dorsally, while the gut tube rolls up and closes ventrally to create a “tube on top of a tube.” The mesoderm, which is another layer of the trilaminar germ disc, holds the tubes together and the lateral plate mesoderm, the middle layer of the germ disc, splits to form a visceral layer associated with the gut and a parietal layer, which along with the overlying ectoderm, forms the lateral body wall. The space between the visceral and parietal layers of lateral plate mesoderm is the primitive body cavity.

These signaling centers are crucial to the proper formation of a limb that is correctly oriented with its corresponding axial polarity in the developing organism. Research has determined that the AER signaling region within the limb bud determines the proximal-distal axis formation of the limb using FGF signals. ZPA signaling establishes the anterior-posterior axis formation of the limb using Shh signals. Additionally, though not known as a specific signaling region like AER and ZPA, the dorsal-ventral axis is established in the limb bud by the competitive Wnt7a and BMP signals that the dorsal ectoderm and ventral ectoderm use respectively. Because all of these signaling systems reciprocally sustain each other’s activity, limb development is essentially autonomous after these signaling regions have been established.

Matsuo-Takasaki, M., Matsumura, M., and Sasai, Y. (2005). An essential role of Xenopus Foxi1a for ventral specification of the cephalic ectoderm during gastrulation. Development 132, 3885-3894. It has been proposed that Notch and/or NODAL, expressed in the vegetal/mesoderm region of the early blastula embryo, could potentially be the inhibitors of FoxI1e.

Dorsoventral patterning is mediated by Wnt7a signals in the overlying ectoderm not the mesoderm. Wnt7a is both necessary and sufficient to dorsalize the limb. Wnt7a also influences the craniocaudal and loss of Wnt7a causes the dorsal side of limbs to become ventral sides and causes missing posterior digits. Replacing Wnt7a signals rescues this defect.

Animals that belong to the basal phyla have holoblastic radial cleavage which results in radial symmetry (see: Symmetry in biology). During cleavage there is a central axis that all divisions rotate about. The basal phyla also has only one to two embryonic cell layers, compared to the three in bilateral animals (endoderm, mesoderm, and ectoderm).

The outer ectodermal layer of the neurula is formed by uniform expansion of the cells at the animal pole, known as the animal cap. The ectoderm then differentiates into neural and epidermal tissue.Keller, R. E., Danilchik, M., Gimlich, R., & Shih, J. (1985). "The function and mechanism of convergent extension during gastrulation of Xenopus laevis" (PDF).

The cadherins are homophilic -dependent glycoproteins. The classic cadherins (E-, N- and P-) are concentrated at the intermediate cell junctions, which link to the actin filament network through specific linking proteins called catenins. Cadherins are notable in embryonic development. For example, cadherins are crucial in gastrulation for the formation of the mesoderm, endoderm, and ectoderm.

A strip of specialized cells called the notochord (A) induces the cells of the ectoderm directly above it to become the primitive nervous system (i.e., neuroepithelium). The neuroepithelium then folds over (B). As the tips of the folds fuse together, a hollow tube (the neural tube) forms (C)—the precursor of the brain and spinal cord.

The pathophysiology of cleft hand is thought to be a result of a wedge-shaped defect of the apical ectoderm of the limb bud (AER: apical ectodermal ridge). Polydactyly, syndactyly and cleft hand can occur within the same hand, therefore some investigators suggest that these entities occur from the same mechanism. This mechanism is not yet defined.

In secondary neurulation, the neural ectoderm and some cells from the endoderm form the medullary cord. The medullary cord condenses, separates and then forms cavities.Formation of the Neural Tube Developmental Biology NCBI Bookshelf These cavities then merge to form a single tube. Secondary neurulation occurs in the posterior section of most animals but it is better expressed in birds.

The ectoderm eventually forms the skin (including hair and nails), mucous membranes and nervous system. The mesoderm forms the skeleton and muscles, heart and circulatory system, urinary and reproductive systems, and connective tissues inside the body. The endoderm forms the gastrointestinal tract (stomach and intestines), the respiratory tract, and the endocrine system (liver and endocrine glands).

Each otic placode recedes below the ectoderm, forms an otic pit and then an otic vesicle. This entire mass will eventually become surrounded by mesenchyme to form the bony labyrinth. Around the 33rd day of development, the vesicles begin to differentiate. Closer to the back of the embryo, they form what will become the utricle and semicircular canals.

This process involves genome-wide DNA demethylation, chromatin reorganization and epigenetic imprint erasure leading to totipotency. DNA demethylation is carried out by a process that utilizes the DNA base excision repair pathway. Morphogenetic movements convert the cell mass into a three layered structure consisting of multicellular sheets called ectoderm, mesoderm and endoderm. These sheets are known as germ layers.

Tornwaldt's disease is a rare benign disorder caused by persistent notochord remnants. This disease almost remains asymptomatic. At about the 10th week of embryonic development, the pharyngeal pouch forms by adhesion of the pharyngeal ectoderm to the cranial end of the notochord. This become closed at the orifice or crusts adhere to the orifice without closing.

The auditory pit, also known as the otic pit, is the first rudiment of the internal ear. It appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. The auditory plate becomes depressed and converted into the auditory pit (or otic pit).

During gastrulation, the cells are differentiated into the ectoderm or mesendoderm, which then separates into the mesoderm and endoderm. The endoderm and mesoderm form due to the nodal signaling. Nodal signaling uses ligands that are part of TGFβ family. These ligands will signal transmembrane serine/threonine kinase receptors, and this will then phosphorylate Smad2 and Smad3.

Beginning in the future neck region, the neural folds of this groove close to create the neural tube. The formation of the neural tube from the ectoderm is called neurulation. The ventral part of the neural tube is called the basal plate; the dorsal part is called the alar plate. The hollow interior is called the neural canal.

In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them.Langman's Medical Embryology, 11th edition. 2010. The mesoderm forms mesenchyme, mesothelium, non-epithelial blood cells and coelomocytes.

The Sonic hedgehog gene also plays a role in attenuating BMP expression, forming the medial hinge point while inhibiting the formation of the dorsolateral hinge points, and in ensuring the proper closure of the neural folds. The prechordal plate, notochord, and non-neural ectoderm are believed to be important inducer tissues which release these chemical signals, in order to trigger neural plate folding. The final adhesion of the converging neural folds is due to several different types of intercellular binding proteins. Cadherins and their CAM receptor molecules, for example, are present in two types in the neural precursor tissue: E-cadherin keeps the cells of the neural plate and surrounding ectoderm adhered to each other, while N-cadherin does the same for the cells of the neural fold.

The epitheloid would then have served as the precursor to the true epithelial tissue of the eumetazoans. In contrast to the model based on functional morphology described earlier, in the Epitheliozoa concept the ventral and dorsal cell layers of the Placozoa are homologs of endoderm and ectoderm, the two basic embryonic cell layers of the eumetazoans — the digestive gastrodermis in the Cnidaria or the gut epithelium in the bilaterally symmetrical Bilateria may have developed from endoderm, whereas ectoderm is, among other things, the precursor to the external skin layer (epidermis). The interior space pervaded by a fiber syncytium in the Placozoa would then correspond to connective tissue in the other animals. It is uncertain whether the calcium ions stored in the syncytium are related to the lime skeletons of many cnidarians.

Great efforts have been made to determine the factors that specify the endoderm and mesoderm. On the other hand, only a few examples of genes that are required for ectoderm specification have been described in the last decade. The first molecule identified to be required for the specification of ectoderm was the ubiquitin ligase Ectodermin (Ecto, TIF1-γ, TRIM33); later, it was found that the deubiquitinating enzyme, FAM/USP9x, is able to overcome the effects of ubiquitination made by Ectodermin in Smad4 (Dupont et al., 2009). Two transcription factors have been proposed to control gene expression of ectodermal specific genes: POU91/Oct3/4Snir, M., Ofir, R., Elias, S., and Frank, D. (2006). Xenopus laevis POU91 protein, an Oct3/4 homologue, regulates competence transitions from mesoderm to neural cell fates.

As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta. On the deep surface of the inner cell mass, a layer of flattened cells, called the endoderm, is differentiated and quickly assumes the form of a small sac, called the yolk sac. Spaces appear between the remaining cells of the mass and, by the enlargement and coalescence of these spaces, a cavity called the amniotic cavity is gradually developed. The floor of this cavity is formed by the embryonic disk, which is composed of a layer of prismatic cells – the embryonic ectoderm, derived from the inner cell mass and lying in apposition with the endoderm.

Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia. After gastrulation, neural crest cells are specified at the border of the neural plate and the non-neural ectoderm. During neurulation, the borders of the neural plate, also known as the neural folds, converge at the dorsal midline to form the neural tube.Brooker, R.J. 2014, Biology, 3rd edn, McGraw-Hill, New York, NY, 1084 Subsequently, neural crest cells from the roof plate of the neural tube undergo an epithelial to mesenchymal transition, delaminating from the neuroepithelium and migrating through the periphery where they differentiate into varied cell types.

PACIFIC SCIENCE, Vol. XXII, July 1968 The name collenchyma in turn was borrowed from botany because of a fancied, essentially irrelevant, resemblance between sponge tissue and a particular class of ground tissue in plants. The collencytes are one of the classes of component cells of the sponges' tissue, loose mesenchyme between the ectoderm and the endoderm in the body wall.Lankester, E. Ray.

Another type of specification is syncytial specification, characteristic of most insect classes. Specification in sea urchins uses both autonomous and conditional mechanisms to determine the anterior/posterior axis. The anterior/posterior axis lies along the animal/vegetal axis set up during cleavage. The micromeres induce the nearby tissue to become endoderm while the animal cells are specified to become ectoderm.

The egg cell is generally asymmetric, having an animal pole (future ectoderm). It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals). Different taxa show different cellular and acellular envelopes englobing the vitelline membrane.

Burns, Tony; et al. (2006) Rook's Textbook of Dermatology CD-ROM. Wiley-Blackwell. . Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The hypoblast helps determine the embryo's body axes, and its migration determines the cell movements that accompany the formation of the primitive streak and its orientation. It develops into the endoderm and helps to orient the embryo and create bilateral symmetry. The other layer of the inner cell mass, the epiblast, differentiates into the three primary germ layers, ectoderm, mesoderm, and endoderm.

The ectoderm and mesoderm of the body trunk are exclusively derived from the teloblast cells in a region called the posterior progress zone. The head of the leech that comes from an unsegmented region, is formed by the first set of micromeres derived from A, B, C and D cells, keeping the bilateral symmetry between the AD and BC cells.

Trichinella is the genus of parasitic roundworms of the phylum Nematoda that cause trichinosis (also known as trichinellosis). Members of this genus are often called trichinella or trichina worms. A characteristic of Nematoda is the one-way digestive tract, with a pseudocoelom (body cavity made up of only an ectoderm and endoderm). The genus was first recognised in a larval form in 1835.

While nasal glial heterotopia (NGH) is the preferred term, synonyms have included nasal glioma. However, this term is to be discouraged, as it implies a neoplasm or tumor, which it is not. By definition, nasal glial heterotopia is a specific type of choristoma. It is not a teratoma, however, which is a neoplasm comprising all three germ cell layers (ectoderm, endoderm, mesoderm).

During the fourth week of human development the neuropore in a normally developing fetus closes. When this process is either interrupted or never initiated, acrania occurs. The desmocranium becomes a membranous coverage instead of forming the epidermis of the scalp. Whether from being blocked by amniotic bands or by just not initiating, the migration of mesenchyme under the ectoderm does not occur.

In addition, it has been determined that unpatterned morphs are recessive to patterned morphs. Lastly, White is seen to be dominant to nearly all morphs. The White morph is produced by a massive deposit of guanine below the hypodermis, which is a structure derived from the ectoderm. Exceptions from simple Mendelian genetics have been observed; for example, White and Red lines exhibit codominance.

Blastomeres isolated from the ICM of mammalian embryos and grown in culture are known as embryonic stem (ES) cells. These pluripotent cells, when grown in a carefully coordinated media, can give rise to all three germ layers (ectoderm, endoderm, and mesoderm) of the adult body.Robertson, Elizabeth , et al. Germ-line transmission of genes introduced into cultured pluripotential cells by retroviral vector.

Following regeneration in L. variegatus, past posterior segments sometimes become anterior in the new body orientation, consistent with morphallaxis. Following amputation, most annelids are capable of sealing their body via rapid muscular contraction. Constriction of body muscle can lead to infection prevention. In certain species, such as Limnodrilus, autolysis can be seen within hours after amputation in the ectoderm and mesoderm.

A saccular dilation in the spermatheca stores spermatozoa received from males during copulation. It can maximize efficiency and use of sperm. Derived from the ectoderm, the spermatheca is covered in fat and tissue and has three main regions: the distal region, the medial region and the proximal region. The coiled distal region is responsible for the control of sperm flow.

During neural induction, noggin and chordin are produced by the dorsal mesoderm (notochord) and diffuse into the overlying ectoderm to inhibit the activity of BMP4. This inhibition of BMP4 causes the cells to differentiate into neural cells. Inhibition of TGF-β and BMP (bone morphogenetic protein) signaling can efficiently induce neural tissue from human pluripotent stem cells, a model of early human development.

Some of the migrating cells displace the hypoblast and create the endoderm, and others migrate between the endoderm and the epiblast to create the mesoderm. The remaining cells form the ectoderm. After that, the epiblast and the hypoblast establish contact with the extraembryonic mesoderm until they cover the yolk sac and amnion. They move onto either side of the prechordal plate.

The authors also remark that the muscle cells found in cnidarians and ctenophores are often contests due to the origin of these muscle cells being the ectoderm rather than the mesoderm or mesendoderm. The origin of true muscles cells is argued by others to be the endoderm portion of the mesoderm and the endoderm. However, Schmid and Seipel counter this skepticism about whether or not the muscle cells found in ctenophores and cnidarians are true muscle cells by considering that cnidarians develop through a medusa stage and polyp stage. They observe that in the hydrozoan medusa stage there is a layer of cells that separate from the distal side of the ectoderm to form the striated muscle cells in a way that seems similar to that of the mesoderm and call this third separated layer of cells the ectocodon.

At the dorsal end of the neural tube, BMPs are responsible for neuronal patterning. BMP is initially secreted from the overlying ectoderm. A secondary signaling center is then established in the roof plate, the dorsal most structure of the neural tube. BMP from the dorsal end of the neural tube seems to act in the same concentration-dependent manner as Shh in the ventral end.

The embryonic disc (or embryonic disk) forms the floor of the amniotic cavity. It is composed of a layer of prismatic cells – the embryonic ectoderm, derived from the inner cell mass and lying in apposition with the endoderm. In humans, it is the stage of development that occurs after implantation and prior to the embryonic folding (e.g. seen between about day 14 to day 21 post fertilization).

The primitive streak extends through this midline and creates the left–right and cranial–caudal body axes, and marks the beginning of gastrulation. This process involves the ingression of mesoderm progenitors and their migration to their ultimate position, where they will differentiate into the mesoderm germ layer that, together with endoderm and ectoderm germ layers, will give rise to all the tissues of the adult organism.

As a result, the floor plate then also begins to secrete SHH, and this will induce the basal plate to develop motor neurons. During the maturation of the neural tube, its lateral walls thicken and form a longtitudinal groove called the sulcus limitans. This extends the length of the spinal cord into dorsal and ventral portions as well. Meanwhile, the overlying ectoderm secretes bone morphogenetic protein (BMP).

Monogenea are Platyhelminthes, so are among the lowest invertebrates to possess three embryonic germ layers—endoderm, mesoderm, and ectoderm. In addition, they have a head region that contains concentrated sense organs and nervous tissue (brain). Like all ectoparasites, monogeneans have well-developed attachment structures. The anterior structures are collectively termed the prohaptor, while the posterior ones are collectively termed the opisthaptor, or simply haptor.

The spinal cord is made from part of the neural tube during development. As the neural tube begins to develop, the notochord begins to secrete a factor known as Sonic hedgehog or SHH. As a result, the floor plate then also begins to secrete SHH, and this will induce the basal plate to develop motor neurons. Meanwhile, the overlying ectoderm secretes bone morphogenetic protein (BMP).

Like in other arthropods it is derived from the endoderm. Unlike the fore- and hindgut, which are derived from ectoderm, it has no cuticular lining. The midgut is surrounded by muscle cells, trachaeae and intermediate tissue, which does not form a fat body like in scorpions and solifuges. The epithelial cells of the midgut are often infected by rickettsia-like parasites, like in some other arachnids.

Arachnids have two kinds of eyes: the lateral and median ocelli. The lateral ocelli evolved from compound eyes and may have a tapetum, which enhances the ability to collect light. With the exception of scorpions, which can have up to five pairs of lateral ocelli, there are never more than three pairs present. The median ocelli develop from a transverse fold of the ectoderm.

The AER is essential for the distal patterning of the limb. Experiments executed in chicken models show Radical fringe is expressed in both the dorsal ectoderm and the AER. This provides evidence that the AER forms from cells already expressing radical fringe, though further evidence is needed to confirm. Grafting experiments have shown that formation of the AER comes from signals in the limb bud mesoderm.

At the end of the second week, a primitive streak appears. The epiblast in this region moves towards the primitive streak, dives down into it, and forms a new layer, called the endoderm, pushing the hypoblast out of the way (this goes on to form the amnion.) The epiblast keeps moving and forms a second layer, the mesoderm. The top layer is now called the ectoderm.

The mesoderm aids in the production of cardiac muscle, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells. The mesoderm germ layer forms in the embryos of triploblastic animals. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm. The formation of a mesoderm leads to the development of a coelom.

P19 cells can be maintained in exponential growth because of a stable chromosomal composition. Because embryonal carcinoma can differentiate into cells of all three germ layers, P19 cells can also differentiate into those ectoderm, mesoderm and endoderm-like cells. When embryonal carcinoma cells are cultured at high density, they start to differentiate. By aggregating the cells into an embryonic body, EC cells can also process differentiation.

The ear develops in the lower neck region and moves upwards as the mandible develops. Unlike structures of the inner and middle ear, which develop from pharyngeal pouches, the ear canal originates from the dorsal portion of the first pharyngeal cleft. It is fully expanded by the end of the 18th week of development. The eardrum is made up of three layers (ectoderm, endoderm and connective tissue).

Epithelial tissue can be derived embryologically from any of the germ layers (ectoderm, endoderm, or mesoderm). To be classified as adenocarcinoma, the cells do not necessarily need to be part of a gland, as long as they have secretory properties. Adenocarcinoma is the malignant counterpart to adenoma, which is the benign form of such tumors. Sometimes adenomas transform into adenocarcinomas, but most do not.

Congenital dermal sinus is an uncommon form of cranial or spinal dysraphism. It occurs in 1 in 2500 live births. It occurs as a dermal indentation, found along the midline of the neuraxis and often presents alongside infection and neurological deficit. Congenital dermal sinus form due to a focal failure of dysjunction between the cutaneous ectoderm and neuroectoderm during the third to eight week of gestation.

The aggregate of cells which eventually form a tooth are derived from the ectoderm of the first branchial arch and the ectomesenchyme of the neural crest.Cate, A. R. Ten, Oral Histology: Development, Structure, and Function, 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 102. . As in all cases of tooth development, the first hard tissue to begin forming is dentin, with enamel appearing immediately afterwards.

A pharyngeal groove (or branchial groove, or pharyngeal cleft) is made up of ectoderm unlike its counterpart the pharyngeal pouch on the endodermal side. The first pharyngeal groove produces the external auditory meatus (ear canal). The rest (2, 3, and 4) are overlapped by the growing 2nd pharyngeal arch, and form the floor of the depression termed the cervical sinus, which opens ventrally, and is finally obliterated.

The planula remain free-living for a short time, after which they settle onto hard substrate and then complete metamorphosis to become its adult form. During metamorphosis, the species destroys most of its endoderm and ectoderm tissues as it undergoes a massive reorganization of its body. In this form it stays attached to a substrate as a polyp. Features on the polyp include a mouth and tentacles.

The syncytial theory rejects the theory of germ layers. During the development of the turbellaria (Acoela), three regions are formed without the formation of germ layers. From this, it was concluded that the germ layers are simultaneously formed during the cellularization process. This is in contrast to germ layer theory in which ectoderm, endoderm and mesoderm (in more complex animals) build up the embryo.

The anus is surrounded by muscles. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation. The anus is surrounded in its length by folds called anal valves, which converge at a line known as the pectinate line. This represents the point of transition between the hindgut and the ectoderm in the embryo.

The chorioallantoic membrane is composed of three layers. The first is the chorionic epithelium that is the external layer present immediately below the shell membrane. It consist of epithelial cells that arise from chorionic ectoderm. The second is the intermediate mesodermal layer that consists of mesenchymal tissue formed by the fusion of the mesodermal layer of the chorion and the mesodermal layer of the allantois.

There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, they are sometimes called diploblastic. The Echinodermata are radially symmetric and exclusively marine, including starfish (Asteroidea), sea urchins, (Echinoidea), brittle stars (Ophiuroidea), sea cucumbers (Holothuroidea) and feather stars (Crinoidea). The largest animal phylum is also included within invertebrates: the Arthropoda, including insects, spiders, crabs, and their kin.

The secondary palate will endochondrally ossify to form the hard palate - the end-stage floor of the nasal cavity. During this time ectoderm and mesoderm of the frontonasal process produce the midline septum. The septum grows down from the roof of the nasal cavity and fuses with the developing palates along the midline. The septum divides the nasal cavity into two nasal passages opening into the pharynx through the definitive choanae.

The exact pathogenesis of neurocutaneous melanosis is not entirely clear, although several factors are thought to contribute to its development. One factor that may contribute to the development of neurocutaneous melanosis is the abnormal postzygotic development of melanoblasts. This mutation would possibly occur within the neural crest of the ectoderm. After the mutation occurs, these cells would then migrate to the meninges as the precursors to the malignant or benign melanocytes.

Tanner stages of breast development. Development of the breasts during the prenatal stage of life is independent of biological sex and sex hormones. During embryonic development, the breast buds, in which networks of tubules are formed, are generated from the ectoderm. These rudimentary tubules will eventually become the matured lactiferous (milk) ducts, which connect the lobules (milk "containers") of the breast, grape-like clusters of alveoli, to the nipples.

The dental lamina is first evidence of tooth development and begins at the sixth week in utero. This is responsible for the cap like structure of the enamel organ. It is important to note that enamel is an ectodermal product as it is originally derived from ectoderm which is the outermost of the three germ layers of the forming embryo. The other two are: the mesoderm and the endoderm.

The sunburst anemone aggressively defends its territory from other anemones which are genetically dissimilar. When it encounters a different genetic colony, the anemones extend specialized tentacles (called acrorhagi). The white tips of acrorhagi have a concentration of stinging cells (nematocytes) and are used solely to deter other colonies from encroaching on their space. The nematocysts sting the ectoderm of the invader, causing tissue necrosis and forcing the competitor to move away.

The ortholog in fruit flies has been suggested to act as a spliceosome. Based on the observed phenotype of incomplete neuroblast differentiation, the ortholog is hypothesized to be involved in splicing namely within the central nervous system. Additional research conclude a cytosine to thymidine nonsense mutation such as that of trichothiodystrophy discussed above has resulted in abnormal development in which tissues of the ectoderm germ layer are affected.

The somites lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are connected to the lateral mesoderm by the intermediate cell mass. Those of the trunk may be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head are usually described as being four in number.

Gonocytes are formed from the differentiation of PGCs. Embryonic cells initiate germ cell development in the proximal epiblast located near the extra-embryonic ectoderm by the release of bone morphogenetic protein 4 (BMP4) and BMP8b. These proteins specify embryonic cells into PGCs expressing the genes PRDM1 and PRDM14 at embryonic day (E) 6.25. The PGCs which are positively stained by alkaline phosphatase and expressing Stella at E7.25 are also specified.

The anterior pituitary is derived from the ectoderm, more specifically from that of Rathke’s pouch, part of the developing hard palate in the embryo. The pouch eventually loses its connection with the pharynx, giving rise to the anterior pituitary. The anterior wall of Rathke's pouch proliferates, filling most of the pouch to form the pars distalis and the pars tuberalis. The posterior wall of the anterior pituitary forms the pars intermedia.

At the early blastoderm stage, Dpp signaling is uniform and low along the dorsal side. A sharp signaling profile emerges at the dorsal midline of the embryo during cellularization, with high levels of Dpp specifying the extraembryonic amnioserosa and low levels specifying the dorsal ectoderm. Dpp signaling also incorporates a positive feedback mechanism that promotes future Dpp binding. The morphogen gradient in embryos is established via a known active transport mechanism.

The earliest signs of segmentation appear during this phase with the formation of parasegmental furrows. This is also when the tracheal pits form, the first signs of structures for breathing. Germ band retraction returns the hindgut to the dorsal side of the posterior pole and coincides with overt segmentation. The remaining stages involve the internalization of the nervous system (ectoderm) and the formation of internal organs (mainly mesoderm).

Trunk neural crest gives rise two populations of cells. One group of cells fated to become melanocytes migrates dorsolaterally into the ectoderm towards the ventral midline. A second group of cells migrates ventrolaterally through the anterior portion of each sclerotome. The cells that stay in the sclerotome form the dorsal root ganglia, whereas those that continue more ventrally form the sympathetic ganglia, adrenal medulla, and the nerves surrounding the aorta.

Pharyngeal arches are formed during the fourth week. Each arch consists of a mesenchymal tissue covered on the outside by ectoderm and on the inside by epithelium of endodermal origin. In human embryology, there are six arches which are separated by pharyngeal grooves externally and pharyngeal pouches internally. These arches contribute to the physical appearance of the embryo because they are the main components that build the face and neck.

During the third week a process called gastrulation creates a mesodermal layer between the endoderm and the ectoderm. This process begins with formation of a primitive streak on the surface of the epiblast. The cells of the layers move between the epiblast and hypoblast and begin to spread laterally and cranially. The cells of the epiblast move toward the primitive streak and slip beneath it in a process called invagination.

The open end of the archenteron is called the blastopore. The Archenteron is labeled as the digestive tube The filopodia—thin fibers formed by the mesenchyme cells—found in a late gastrula contract to drag the tip of the archenteron across the blastocoel. The endoderm of the archenteron will fuse with the ectoderm of the blastocoel wall. At this point gastrulation is complete, and the gastrula has a functional digestive tube.

It has been suggested that zero-order ultrasensitivity may generate thresholds during development allowing for the conversion of a graded morphogen input to a binary switch-like response. Melen et al. (2005) have found evidence for such a system in the patterning of the Drosophila embryonic ventral ectoderm. In this system, graded mitogen activated protein kinase (MAPK) activity is converted to a binary output, the all-or-none degradation of the Yan transcriptional repressor.

Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism. The endoderm of vertebrates produces tissue within the lungs, thyroid, and pancreas. The mesoderm aids in the production of cardiac muscle, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells.

The macromeres give rise to the posterior larval ectoderm and the vegetal micromeres give rise to the internal endomesodermal tissues. Studies done on the potential of the embryo at different stages have shown that at both the two and four cell stage of development P. flava blastomeres can go on to give rise to a tornaria larvae, so fates of these embryonic cells don’t seem to be established till after this stage.

Phakomatoses, or phacomatosis pigmentovascularis (PPV), is the term used for a group of rare syndromes involving structures arising from the embryonic ectoderm. These are characterised by vascular and pigmentary birthmarks or skin lesions, and often involving multiple organ systems in the body. The term is used to describe the “association of a vascular nevus with an extensive pigmentary nevus”. These multi-system disorders involve the ectodermal structures like central nervous system, skin and eyes.

The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege. The ectospermalege is derived from the ectoderm. It consists of a groove in the right-handed posterior margin of the fifth sclerite, overlying a pleural membrane. In order to access the female's haemocoel during traumatic insemination, male bed bugs insert their needle-like penisRyne, C. (2009) "Homosexual interactions in bed bugs: alarm pheromones as male recognition signals," Animal Behaviour, 78, 1471–1475.

After the disc becomes tri-layered, it undergoes growth and folding to transform it from disc to cylinder shaped. The layer of ectoderm and mesoderm in the dorsal axis grow ventrally to meet at the midline. Simultaneously, the cephalic (head) and caudal (tail) ends of these layers of the disc fold ventrally to meet the lateral folds in the center. The meeting of both axis at the center form the umbilical ring.

Neurulation, the formation of the central nervous system, is different in fishes than in most other chordates. Convergence and extension in the epiblast recruits presumptive neural cells from the epiblast towards the midline where they form a neural keel. A neural keel is a band of neural precursors that develops a slit like lumen to eventually become the neural tube. The neural tube begins as a solid cord formed from the ectoderm.

This cord then sinks into the embryo and becomes hollow, forming the neural tube. This process contrasts with the process in other chordates, which occurs by an infolding of the ectoderm to form a hollow tube. Throughout the years advances in research have shown that neural formation relies on interactions between extrinsic signaling factors and intrinsic transcription factors. Extrinsic signals involved are BMP, Wnt, and FGF and intrinsic transcription factors like SoxB1 related genes.

The tentacles are organs which serve both for the tactile sense and for the capture of food. Polyps extend their tentacles, particularly at night, often containing coiled stinging cells (cnidocytes) which pierce, poison and firmly hold living prey paralysing or killing them. Polyp prey includes plankton such as copepods and fish larvae. Longitudinal muscular fibers formed from the cells of the ectoderm allow tentacles to contract to convey the food to the mouth.

As cleavage continues, the cavity expands to become the developed blastocoel. The blastocoel is a crucial component of amphibian embryo development. It permits cell migration during gastrulation and prevents the cells beneath the blastocoel from interacting prematurely with the cells above the blastocoel. For instance, the blastocoel prevents the vegetal cells destined to become endoderm from coming in contact with those cells in the ectoderm fated to give rise to the skin and nerves.

They are derived from the ectoderm germ layer, but are sometimes called the fourth germ layer because they are so important and give rise to so many other types of cells.Gilbert S. F. "Developmental biology." Sinauer Associates, Massachusetts, 2010 p373 - 389. They migrate throughout the body and create a large number of differentiated cells such as neurons, glial cells, pigment-containing cells in skin, skeletal tissue cells in the head, and many more.

R-spondin 2 also known as roof plate-specific spondin-2 is a protein that in humans that is encoded by the RSPO2 gene. R-spondin 2 synergizes with Wnt to activate beta-catenin. RSPO2 has been proposed to regulate craniofacial patterning and morphogenesis within pharyngeal arch 1 through ectoderm- mesenchyme signaling via the endothelin-Dlx5/6 pathway. In dogs, a variant on the Rspo2 gene is associated moustache and eyebrow thickness.

Cell death in arthropods occurs first in the nervous system when ectoderm cells differentiate and one daughter cell becomes a neuroblast and the other undergoes apoptosis. Furthermore, sex targeted cell death leads to different neuronal innervation of specific organs in males and females. In Drosophila, PCD is essential in segmentation and specification during development. In contrast to invertebrates, the mechanism of programmed cell death is found to be more conserved in vertebrates.

GDF6 belongs to the transforming growth factor beta superfamily and may regulate patterning of the ectoderm by interacting with bone morphogenetic proteins, and control eye development. Growth differentiation factor 6 (GDF6) is a regulatory protein associated with growth and differentiation of developing embryos. GDF6 is encoded by the GDF6 gene. It is a member the transforming growth factor beta superfamily which is a group of proteins involved in early regulation of cell growth and development.

At the end of the fourth week limb development begins. Limb buds appear on the ventrolateral aspect of the body. They consist of an outer layer of ectoderm and an inner part consisting of mesenchyme which is derived from the parietal layer of lateral plate mesoderm. Ectodermal cells at the distal end of the buds form the apical ectodermal ridge, which creates an area of rapidly proliferating mesenchymal cells known as the progress zone.

The dorsal nerve cord is a unique feature to chordates, and it is mainly found in the Vertebrata chordate subphylum. The dorsal nerve cord is only one embryonic feature unique to all chordates, among the other four chordate features-- a notochord, a post-anal tail, an endostyle, and pharyngeal slits. The dorsal hollow nerve cord is a hollow cord dorsal to the notochord. It is formed from a part of the ectoderm that rolls, forming the hollow tube.

In the embryo, the formation of the neural folds originates from the area where the neural plate and the surrounding ectoderm converge. This region of the embryo is formed after gastrulation, and consists of epithelial tissue. Here, the epithelial cells elongate by means of microtubule polymerization, increasing their height. The thumbnail below shows this process, as well as the subsequent formation of the neural crest cells and the neural tube, which arise from the joining of the neural folds.

Ear development begins in about the third week of human embryonic development. Beginning with the formation of the Otic Placodes which are an extension of the early hind brain. By the fourth week of development the otic placodes invaginate, or sink inward forming pits which close themselves off for the outer surface ectoderm and begin forming the inner ear labyrinthe on the inside. Outer ear development begins in about the fifth week of human embryonic development.

Mesentoblasts, also called 4d cells, are the cells from which the mesoderm originates. Mesentoblasts are found in the blastopore area between the endoderm and the ectoderm. In protostomes the embryos are mosaic, so mesentoblast removal will result in failure of formation of the mesoderm and other structures related to the mesoderm, which in turn will give abnormal embryos. The mesentoblast migrates to the blastocoel where it reproduces to form a mass of cells that becomes the mesoderm.

This development is induced by the ventral part of the forebrain. In the sixth week the ectoderm in each nasal placode invaginates to form an indented oval-shaped pit, which forms a surrounding raised ridge of tissue. Each nasal pit forms a division between the ridges, into a lateral nasal process on the outer edge, and a medial nasal process on the inner edge. In the sixth week the nasal pits deepen as they penetrate into the underlying mesenchyme.

A mutation in the GSC gene in Drosophila is lethal. Gsc gene promotes the formation of Spemann’s Organizer. This organizer prevents BMP-4 from inducing the ectoderm in the future head region of the embryo to become epidermis; it instead allows the future head region to form neural folds, which will eventually turn into the brain and spinal cord. For normal anterior development to occur, Spemann’s organizer cannot express the Xwnt-8 or BMP-4 transcription factors.

The diencephalon is a division of the forebrain (embryonic prosencephalon), and is situated between the telencephalon and the midbrain (embryonic mesencephalon). It consists of structures that are on either side of the third ventricle, including the thalamus, the hypothalamus, the epithalamus and the subthalamus. The diencephalon is one of the main vesicles of the brain formed during embryogenesis. During the third week of development a neural tube is created from the ectoderm, one of the three primary germ layers.

The eye-spots act as photoreceptors and are used to move away from light sources. Planaria have three germ layers (ectoderm, mesoderm, and endoderm), and are acoelomate (they have a very solid body with no body cavity). They have a single-opening digestive tract; in Tricladida planarians this consists of one anterior branch and two posterior branches. Planarians move by beating cilia on the ventral dermis, allowing them to glide along on a film of mucus.

After reaching its maximum height, the AER in mouse limb buds flattens and eventually become indistinguishable from the dorsal and ventral ectoderm. The structure of the human AER is similar to the mouse AER. In addition to wings in chicks and forelimbs in mice, pectoral fins in zebrafish serve as a model to study vertebrate limb formation. Despite fin and limb developmental processes share many similarities, they exhibit significant differences, one of which is the AER maintenance.

As nodal signaling give rise to ectoderm and mesoderm, neuroectoderm formation requires blocking nodal signaling which is accomplished by the expression of nodal antagonist, Cerberus. The role of nodal signaling reemerges later in development when nodal signaling is required to specify ventral cell neural patterning. Loss of function of Cyclops or oep in zebrafish results in cyclopic embryos characterized by a lack of medial floor plate and ventral forebrain. Not all nodals result in the formation of mesoectoderm.

The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm, forming the parietal layer and the second surrounds the endoderm or alimentary canal forming the visceral layer. The space between the parietal layer and the visceral layer is known as the coelom or body cavity. In Deuterostomes, the coelom forms by enterocoely. The archenteron wall produces buds of mesoderm, and these mesodermal diverticula hollow to become the coelomic cavities.

The earliest forms of laminar organization are shown in the diploblastic and triploblastic formation of the germ layers in the embryo. In the first week of human embryogenesis two layers of cells have formed, an external epiblast layer (the primitive ectoderm), and an internal hypoblast layer (primitive endoderm). This gives the early bilaminar disc. In the third week in the stage of gastrulation epiblast cells invaginate to form endoderm, and a third layer of cells known as mesoderm.

Noggin proteins play a role in germ layer-specific derivation of specialized cells. The formation of neural tissues, the notochord, hair follicles, and eye structures arise from the ectoderm germ layer. Noggin activity in the mesoderm gives way to the formation of cartilage, bone and muscle growth, and in the endoderm noggin is involved in the development of the lungs. Early craniofacial development is heavily influenced by the presence of noggin in accordance with its multiple tissue-specific requirements.

The ectoderm forms the skin, nails, hair, cornea, lining of the internal and external ear, nose, sinuses, mouth, anus, teeth, pituitary gland, mammary glands, eyes, and all parts of the nervous system. Approximately 18 days after fertilization, the embryo has divided to form much of the tissue it will need. It is shaped like a pear, where the head region is larger than the tail. The embryo's nervous system is one of the first organic systems to grow.

Pharyngeal arches are tissues composed of mesoderm-derived cells enclosed by an external ectoderm and an internal endoderm. Once the caudal pharyngeal arches are formed, cardiac neural crest complexes will migrate towards these and colonise in arches 3, 4 and 6. Cells leading this migration maintain contact with the extracellular matrix and contain the protein filopedia that acts as extensions towards the ectodermal pharyngeal arches. A range of secreted factors ensure appropriate directionality of the cells.

In the lateral regions of the embryo, low nuclear concentrations of Dorsal lead to the expression of rhomboid which identifies future neuroectoderm. More dorsally, active Dpp signaling represses rhomboid thus confining it to the lateral blastoderm nuclei. At the dorsal side of the embryo, blastoderm nuclei where this is little or no nuclear dorsal protein express zerknüllt, tolloid, and decapentaplegic (Dpp). This leads to the specification of non-neural ectoderm and later in the blastula stage to anmioserosa.

In fish the pouches line up with the clefts, and these thin segments become gills. In mammals the endoderm and ectoderm not only remain intact but also continue to be separated by a mesoderm layer. The development of the pharyngeal arches provides a useful landmark with which to establish the precise stage of embryonic development. Their formation and development corresponds to Carnegie stages 10 to 16 in mammals, and Hamburger–Hamilton stages 14 to 28 in the chicken.

The discovery that expression of only four transcription factors was necessary to induce pluripotency allowed future regenerative medicine research to be conducted considering minor manipulations. Loss of pluripotency is regulated by hypermethylation of some Sox2 and Oct4 binding sites in male germ cells and post-transcriptional suppression of Sox2 by miR134. Varying levels of Sox2 affect embryonic stem cells' fate of differentiation. Sox2 inhibits differentiation into the mesendoderm germ layer and promotes differentiation into neural ectoderm germ layer.

Similar to lens, cornea is a transparent, avascular tissue derived from the ectoderm that is responsible for focusing light onto the retina. However, unlike lens, cornea depends on the air-cell interface and its curvature for refraction. Early immunology studies have shown that BCP 54 comprises 20–40% of the total soluble protein in bovine cornea. Subsequent studies have indicated that BCP 54 is ALDH3, a tumor and xenobiotic-inducible cytosolic enzyme, found in human, rat, and other mammals.

During retinal development, SIX3 has been proven to hold a key responsibility in the activation of Pax6, the master regulator of eye development. Furthermore, SIX3 assumes its activity in the PLE (presumptive lens ectoderm), the region in which the lens is expected to develop. If its presence is removed from this region, the lens fails to thicken and construct itself to its proper morphological state. Also, SIX3 plays a strategic role in the activation of SOX2.

The eyes begin to develop as a pair of diverticula (pouches) from the lateral aspects of the forebrain. These diverticula make their appearance before the closure of the anterior end of the neural tube; after the closure of the tube around the 4th week of development, they are known as the optic vesicles. Previous studies of optic vesicles suggest that the surrounding extraocular tissues – the surface ectoderm and extraocular mesenchyme – are necessary for normal eye growth and differentiation.Fuhrmann, S. (2010).

The hindgut gives rise to the region from the distal third of the transverse colon to the upper part of the anal canal. The distal part of the anal canal originates from the ectoderm. The hindgut enters the posterior region of the cloaca (future anorectal canal), and the allantois enters the anterior region (future urogenital sinus). The urorectal septum divides the two regions and breakdown of the cloacal membrane covering this area provides communication to the exterior for the anus and urogenital sinus.

During embryogenesis, the inner cell mass (ICM) is separated from the trophoblast. The stem cells derived from the ICM and trophectoderm have been found to express high levels of Oct3/4 and Rex1. As the ICM matures and begins to form the epiblast, and primitive ectoderm, the cells in the ICM have been found to be a heterogenous population, with varying levels of Rex1 expression. Rex1−/Oct3/4− triggers trophectoderm differentiation, while Rex1+/Oct3/4+ cells predominantly differentiate into primitive endoderm and mesoderm.

Trichothiodystrophy (TTD) is an autosomal recessive inherited disorder characterised by brittle hair and intellectual impairment. The word breaks down into tricho – "hair", thio – "sulphur", and dystrophy – "wasting away" or literally "bad nourishment". TTD is associated with a range of symptoms connected with organs of the ectoderm and neuroectoderm. TTD may be subclassified into four syndromes: Approximately half of all patients with trichothiodystrophy have photosensitivity, which divides the classification into syndromes with or without photosensitivity; BIDS and PBIDS, and IBIDS and PIBIDS.

The endoderm is the inner most germ layer of the embryo which gives rise to gastrointestinal and respiratory organs by forming epithelial linings and organs such as the liver, lungs, and pancreas. The mesoderm or middle germ layer of the embryo will form the blood, heart, kidney, muscles, and connective tissues. The ectoderm or outermost germ layer of the developing embryo forms epidermis, the brain, and the nervous system. Neural precursor cells fold and elongate to form the neural tube.

The pharynx is muscular and lined by teeth. The anus is terminal, although in Priapulus one or two hollow ventral diverticula of the body-wall stretch out behind it. The nervous system consists of a nerve ring around the pharynx and a prominent cord running the length of the body with ganglia and longitudinal and transversal neurites consistent with an orthogonal organisation. The nervous system retains a basiepidermal configuration with a connection with the ectoderm, forming part of the body wall.

Chick embryo of thirty-three hours’ incubation, viewed from the dorsal aspect. X 30 The mesoderm forms at the same time as the other two germ layers, the ectoderm and endoderm. The mesoderm at either side of the neural tube is called paraxial mesoderm. It is distinct from the mesoderm underneath the neural tube which is called the chordamesoderm that becomes the notochord. The paraxial mesoderm is initially called the “segmental plate” in the chick embryo or the “unsegmented mesoderm” in other vertebrates.

Delta Theta Tau Sorority is a service sorority and raises money through various efforts for many different charities. Over the last ten years, Delta Theta Tau has contributed a great deal of time and money to the National Foundation for Ectodermal Dysplasias (NFED). The ectodermal dysplasia (ED) syndromes are a group of about 150 heritable disorders that affect the ectoderm, the outer layer of tissue in a developing baby. ED syndromes affect both males and females of all races and ethnic groups.

Each one functions as a separate endocrine organ, and both are circumventricular organs. The anterior pituitary contains non-neural secretory cells derived from oral ectoderm which are indirectly controlled by "releasing hormones" from the median eminence of the hypothalamus, through the hypophyseal portal circulation. The posterior pituitary consists of axonal projections that directly extend from cell bodies in the hypothalamus, through the infundibulum. It is located in the sella turcica of the sphenoid bone at the base of the skull.

In Germany, Mall found his peers to be especially driven and better educated; they were independently planning their future studies. Mall heavily valued the freedom of choice and the liberty afforded to him while studying in Germany. In 1885, Mall went to Leipzig to begin his career in research under the guidance of Wilhelm His. Mall's first project resulted in evidence that contradicted his mentor's position on the origin of the thymus, concluding that it develops from the endoderm instead of the ectoderm.

Gastrulation is the next phase of embryonic development, and involves the development of two or more layers of cells (germinal layers). Animals that form two layers (such as Cnidaria) are called diploblastic, and those that form three (most other animals, from flatworms to humans) are called triploblastic. During gastrulation of triploblastic animals, the three germinal layers that form are called the ectoderm, mesoderm, and endoderm. All tissues and organs of a mature animal can trace their origin back to one of these layers.

In mice, Lim-1 acts in the early development of the mesoderm and ectoderm layers of the developing embryo. The factor is induced by the increasing concentrations of Cerebrus, DKK1, and Nodal around day 7–9 in the mouse embryo. Lim-1 contributes to the formation of the anterior portion of the developing head containing the forebrain and midbrain. Research studies have shown that knocking out Lim-1 in mice will cause a range of head deformities, including the complete lack of formation of the head.

In the absence of these signals, ectoderm reverts to its default state of neural tissue. Four of the secreted molecules from the organizer, chordin, noggin, follistatin and Xenopus nodal-related-3 (Xnr-3), directly interact with BMP-4 and block its ability to bind to its receptor. Thus, these molecules create a gradient of BMP-4 along the dorsal/ventral axis of the mesoderm. BMP-4 mainly acts in trunk and tail region of the embryo while a different set of signals work in the head region.

Mollusc shells in Manchester Museum The shell-secreting area is differentiated very early in embryonic development. An area of the ectoderm thickens, then invaginates to become a "shell gland". The shape of this gland is tied to the form of the adult shell; in gastropods, it is a simple pit, whereas in bivalves, it forms a groove which will eventually become the hinge line between the two shells, where they are connected by a ligament. The gland subsequently evaginates in molluscs that produce an external shell.

Nacre, commonly known as mother of pearl, forms the inner layer of the shell structure in some groups of gastropod and bivalve molluscs, mostly in the more ancient families such as top snails (Trochidae), and pearl oysters (Pteriidae). Like the other calcareous layers of the shell, the nacre is created by the epithelial cells (formed by the germ layer ectoderm) of the mantle tissue. However, nacre does not seem to represent a modification of other shell types, as it uses a distinct set of proteins.

Engrailed (En) 1 is a homeobox gene that helps primarily regulate development in the dorsal midbrain and anterior hindbrain (cerebellum and colliculi) of humans. The expression of En1 is regulated until 13 days after fertilization by Fgf8, which controls the development of the forebrain and hindbrain. En1 is first expressed in this region on day 9.5 after fertilization for about 12 hours until En2 is expressed. After En2 expression, En1 is expressed again in other tissues such as somites and limb ectoderm throughout development.

Gastrulation establishes the three germ layers: ectoderm, mesoderm and endoderm. It seems that complications such as defects in the urogenital system as mentioned above can be possibly due to malformations in the intermediate mesoderm. A four-hour operation to insert silicone bags between her legs to stretch the skin was successfully completed on February 8, 2005. A successful operation to separate her legs to just above the knee took place May 31, 2005, in a "Solidarity Hospital" in the district of Surquillo in Lima.

Transcription factor AP-2 alpha is expressed in ectoderm and in neural-crest cells migrating from the cranial folds during closure of the neural tube in the mouse. Cranial neural crest cell provides patterning information for craniofacial morphogenesis and generate most of the skull bones and the cranial ganglia. AP-2 alpha knockout mice die perinatally with cranio-abdominoschisis and severe dysmorphogenesis of the face, skull, sensory organs, and cranial ganglia. Homozygous knockout mice also have neural tube defects followed by craniofacial and body wall abnormalities.

Limb formation begins in the morphogenetic limb field. Limb formation results from a series of reciprocal tissue interactions between the mesenchyme of the lateral plate mesoderm and the overlying ectodermally derived epithelial cells. Cells from the lateral plate mesoderm and the myotome migrate to the limb field and proliferate to the point that they cause the ectoderm above to bulge out, forming the limb bud. The lateral plate cells produce the cartilaginous and skeletal portions of the limb while the myotome cells produce the muscle components.

The eyelashes of the human embryo develop from the ectoderm between the 22nd and 26th week of pregnancy. Natural eyelashes do not grow beyond a certain length, and fall off by themselves without any need for trimming. Eyelashes take about seven to eight weeks to grow back if pulled out, but constant pulling may lead to permanent damage. Their color may differ from that of the hair, although they tend to be dark on someone with dark hair and lighter on someone with light hair.

Once the egg has become multicellular and positioned its germ layers with ectoderm on the outside, mesoderm in the middle, and endoderm on the inside body axes have to be determined for proper development. A dorsal-ventral axis has to form and major proteins involved are BMP and Wnts. Both proteins are made in the ventral and lateral portions of the developing embryo. BMP2B induces cells to have ventral and lateral fates while factors such as chordin can block BMPs to dorsalize the tissue.

Dental pulp stem cells (DPSCs) are stem cells present in the dental pulp, which is the soft living tissue within teeth. They are pluripotent, as they can form embryoid body-like structures (EBs) in vitro and teratoma-like structures that contained tissues derived from all three embryonic germ layers when injected in nude mice. DPSCs can differentiate in vitro into tissues that have similar characteristics to mesoderm, endoderm and ectoderm layers. DPSCs were found to be able to differentiate into adipocytes and neural-like cells.

Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm, which will develop into the membranous labyrinth of the inner ear. This labyrinth is a continuous epithelium, giving rise to the vestibular system and auditory components of the inner ear.Freyer L, Aggarwal V, Morrow BE. Dual embryonic origin of the mammalian otic vesicle forming the inner ear. Development. 2011;138(24):5403-5414. doi:10.1242/dev.069849.

The integument of an organ in zoology typically would comprise membranes of connective tissue such as those around a kidney or liver. In referring to the integument of an animal, the usual sense is its skin and its derivatives: the integumentary system, where "integumentary" is a synonym for "cutaneous". In arthropods, the integument, or external "skin", consists of a single layer of epithelial ectoderm from which arises the cuticle, an outer covering of chitin the rigidity of which varies as per its chemical composition.

In the outer part of the intermediate mesoderm, immediately under the ectoderm, in the region from the fifth cervical segment to the third thoracic segment, a series of short evaginations from each segment grows dorsally and extends caudally, fusing successively from before backward to form the pronephric duct. This continues to grow caudally until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the mesonephric duct. Thus, the mesonephric duct remains after the atrophy of the pronephros duct.

In each zone a different combination of developmental control genes is upregulated. These genes encode transcription factors which upregulate new combinations of gene activity in each region. Among other functions, these transcription factors control expression of genes conferring specific adhesive and motility properties on the cells in which they are active. Because of these different morphogenetic properties, the cells of each germ layer move to form sheets such that the ectoderm ends up on the outside, mesoderm in the middle, and endoderm on the inside.

Development, 89(Supplement), 185-209. In reptilian embryos, beginning in the late-stage neurula and carrying over into the early stages of organogenesis, extra-embryonic membrane tissues comprising the yolk sac, chorion, and amnion become distinct from the tissues of the embryo. The mesoderm splits to create the extra-embryonic coelom, which consists of two layers. The vascularized mesoderm-endoderm inner layer, termed the splanchnopleure, develops into the yolk sac, while the nonvascularized ectoderm-mesoderm outer layer, termed the somatopleure, becomes the amnion and chorion.

Review of literature reveals extensive associated findings in trichothiodystrophy. Amino acid analyses of control hair when compared with those of patients with the Sabinas syndrome showed very striking differences with regard to content of sulphur amino acids. As in previous descriptions of amino acid abnormalities in the trichorrhexis nodosa of arginosuccinicaciduria, there were increases in lysine, aspartic acid, alanine, leucine, isoleucine, and tyrosine. Trichothiodystrophy represents a central pathologic feature of a specific hair dysplasia associated with several disorders in organs derived from ectoderm and neuroectoderm.

SHH in particular is needed for growth of epithelial cervical loops where the outer and inner epitheliums join and form a reservoir for dental stem cells. After the primary enamel knots are apoptosed, the secondary enamel knots are formed. The secondary enamel knots secrete SHH in combination with other signaling molecules to thicken the oral ectoderm and begin patterning the complex shapes of the crown of a tooth during differentiation and mineralization. In a knockout gene model absence of SHH is indicative of holoprosencephaly.

The neural fold is a structure that arises during neurulation in the embryonic development of both birds and mammals among other organisms. This structure is associated with primary neurulation, meaning that it forms by the coming together of tissue layers, rather than a clustering, and subsequent hollowing out, of individual cells (known as secondary neurulation). In humans, the neural folds are responsible for the formation of the anterior end of the neural tube. The neural folds are derived from the neural plate, a preliminary structure consisting of elongated ectoderm cells.

Epithelial dysplasia consists of an expansion of immature cells (such as cells of the ectoderm), with a corresponding decrease in the number and location of mature cells. Dysplasia is often indicative of an early neoplastic process. The term dysplasia is typically used when the cellular abnormality is restricted to the originating tissue, as in the case of an early, in-situ neoplasm. Dysplasia, in which cell maturation and differentiation are delayed, can be contrasted with metaplasia, in which cells of one mature, differentiated type are replaced by cells of another mature, differentiated type.

A: Human embryonic stem cells (cell colonies that are not yet differentiated). B: Nerve cells In cell biology, pluripotency (Lat. pluripotentia, "ability for many [things]") refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous system), but not into extra-embryonic tissues like the placenta. However, cell pluripotency is a continuum, ranging from the completely pluripotent cell that can form every cell of the embryo proper, e.g.

Trophoblasts (from Greek 'trephein': to feed; and 'blastos': germinator) are cells that form the outer layer of a blastocyst, and are present four days post fertilization in humans. They provide nutrients to the embryo and develop into a large part of the placenta. They form during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures and do not directly contribute to the embryo. After gastrulation, the trophoblast is contiguous with the ectoderm of the embryo, and is referred to as the trophectoderm.

The medial nasal processes provide the crest and the tip of the nose, and the lateral nasal processes form the alae or sides of the nose. The frontonasal process is a proliferation of mesenchyme in front of the brain vesicles, and makes up the upper border of the stomadeum. During the fifth week the maxillary processes increase in size and at the same time the ectoderm of the frontonasal process becomes thickened at its sides and also increases in size, forming the nasal placodes. The nasal placodes are also known as the olfactory placodes.

Early inductive effects of the axial mesoderm upon the overlying neural ectoderm is the mechanism that establishes the length dimension upon the brain primordium, jointly with establishing what is ventral in the brain (close to the axial mesoderm) in contrast with what is dorsal (distant from the axial mesoderm). Apart from the lack of a causal argument for introducing the axis in the telencephalon, there is the obvious difficulty that there is a pair of telencephalic vesicles, so that a bifid axis is actually implied in these outdated versions.

The ectoderm produces tissues within the epidermis and aids in the formation of neurons within the brain, and melanocytes. The cells of each of the three germ layers undergo differentiation, a process where less-specialized cells become more- specialized through the expression of a specific set of genes. Cell differentiation is driven by cell signaling cascades. Differentiation is influenced by extracellular signals such as growth factors that are exchanged to adjacent cells which is called juxtracrine signaling or to neighboring cells over short distances which is called paracrine signaling.

There are two classes of genes that are responsible for the organizer's activity: transcription factors and secreted proteins. Goosecoid (which has a homology between bicoid and gooseberry) is the first known gene to be expressed in the organizer and is both sufficient and necessary to specify a secondary axis. The organizer induces ventral mesoderm to become lateral mesoderm, induces the ectoderm to form neural tissue and induces dorsal structures in the endoderm. The mechanism behind these inductions is an inhibition of the bone morphogenetic protein 4 signaling pathway that ventralizes the embryo.

Within a group of organisms, taxa showing morphological extremes are favorite objects in constructional morphology, and the West African Sand Dollar is no exception. The West African Sand Dollar is a bilaterian (animals with bilateral symmetry) even though adults possess radial symmetry, because the larvae possess bilateral symmetry. Since the organism is a bilaterian, it has three tissue layers: endoderm, ectoderm, and mesoderm. The sand dollar is part of the phylum echinodermata, and so the organism has an endoskeleton composed of calcareous ossicles which grow from the mesodermal tissue.

Expanding use of the microscope coupled with a new technique in the late 18th century unveiled the developing chick for close-up examination. By cutting a hole in the eggshell and covering it with another piece of shell, scientists were able to look directly into the egg while it continued to develop without dehydration. Soon studies of the developing chick identified the three embryonic germ layers: ectoderm, mesoderm and endoderm, giving rise to the field of embryology. Host versus graft response was first described in the chicken embryo.

In the outer part of the intermediate mesoderm, immediately under the ectoderm, in the region from the fifth cervical segment to the third thoracic segment, a series of short evaginations from each segment grows dorsally and extends caudally, fusing successively from before backward to form the pronephric duct. This continues to grow caudally until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the Wolffian duct. Thus, the Wolffian duct is what remains of the pronephric duct after the atrophy of the pronephros.

Murine embryoid bodies in suspension culture after 24 hours of formation from embryonic stem cells. Embryoid bodies are a common in vitro pluripotency test for stem cells and their size needs to be controlled to induce directed differentiation to specific lineages. High throughput formation of uniform sized embryoid bodies with microwells and microfluidics allows easy retrieval and more importantly, scale up for clinical contexts. Actively controlling embryoid body cell organization and architecture can also direct stem cell differentiation using microfluidic gradients of endoderm-, mesoderm- and ectoderm-inducing factors, as well as self-renewal factors.

The vestibular lamina is usually contrasted with the dental lamina, which develops concurrently and is involved with developing teeth. Both the vestibular lamina and the dental lamina arise from a group of epithelial cells, called the primary epithelial band. The vestibular lamina develops at 6th week of the intrauterine life as a result of proliferation of the primitive ectoderm that lines the primitive oral cavity. The cells enlarge and then degenerate to form a cleft that separates the lips and cheeks at one side from the developing jaws and teeth at the other side.

During early vertebrate development, the stage is set for the specification of the three germ layers : endoderm, mesoderm and ectoderm,(1) which will give rise to the adult organism. The mesoderm will eventually differentiate into numerous tissues including muscles and blood.(2) This process requires the precise integration of a variety of signaling pathways such as the transforming growth factor type β (TGFβ), fibroblast growth factor (FGF), bone morphogenetic protein (BMP), and Wnt, to achieve the induction, specification, formation and differentiation of the mesoderm layer within a given time and space.

Inhibition of FoxI1e mRNA maturation by a splice-blocking morpholino shows malformations in the development of epidermis and pervious system and down- regulates of ectoderm specific genes, whereas FoxI1e over-expression inhibits the formation of mesoderm and endoderm. Vegetal structures form late blastula masses that normally would give rise to endoderm and mesoderm, when injected with FoxI1e mRNA, they are able to express ectodermal specific markers (pan- ectodermal E-cadherin, epithelial cytokeratin, neural crest marker Slug and neural marker Sox-2) while endodermal markers (endodermin, Xsox17a) decreased in expression.

The term conception commonly refers to "the process of becoming pregnant involving fertilization or implantation or both". Its use makes it a subject of semantic arguments about the beginning of pregnancy, typically in the context of the abortion debate. Upon gastrulation, which occurs around 16 days after fertilisation, the implanted blastocyst develops three germ layers, the endoderm, the ectoderm and the mesoderm, and the genetic code of the father becomes fully involved in the development of the embryo; later twinning is impossible. Additionally, interspecies hybrids survive only until gastrulation and cannot further develop.

A trilaminar embryo (or trilaminary blastoderm, or trilaminar germ disk) is an early stage in the development of triploblastic organisms, which include humans and many other animals. It is an embryo which exists as three different germ layers - the ectoderm, the mesoderm and the endoderm. These layers are arranged on top of each other like a stack of paper, giving rise to the name trilaminar, or "three-layered". These three layers arise early in the third week (after gastrulation) from the epiblast (a portion of the mammalian inner cell mass).

Inhibition of the BMP4 signal (by chordin, noggin, or follistatin) causes the ectoderm to differentiate into the neural plate. If these cells also receive signals from FGF, they will differentiate into the spinal cord; in the absence of FGF the cells become brain tissue. While overexpression of BMP4 expression can lead to ventralization, inhibition with a dominant negative may result in complete dorsalization of the embryo or the formation of two axises. It is important to note that mice in which BMP4 was inactivated usually died during gastrulation.

Cells from the lateral plate mesoderm and the myotome migrate to the limb field and proliferate to create the limb bud. The lateral plate cells produce the cartilaginous and skeletal portions of the limb while the myotome cells produce the muscle components. The lateral plate mesodermal cells secrete a fibroblast growth factor (FGF7 and FGF10, presumably) to induce the overlying ectoderm to form an important organizing structure called the apical ectodermal ridge (AER).The AER reciprocatively secretes FGF8 and FGF4 which maintains the FGF10 signal and induces proliferation in the mesoderm.

The frontonasal process, or frontonasal prominence is one of the five swellings that develop to form the face. The frontonasal process is unpaired, and the others are the paired maxillary prominences, and the paired mandibular prominences. During the fourth week of embryonic development, an area of thickened ectoderm develops, on each side of the frontonasal process called the nasal placodes or olfactory placodes, and appear immediately under the forebrain. By invagination these areas are converted into two nasal pits, which indent the frontonasal prominence and divide it into medial and lateral nasal processes.

A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals more complex than the sponge) produce two or three primary germ layers. Some animals, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Other animals such as chordates produce a third layer (the mesoderm) between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal’s tissues and organs through the process of organogenesis.

In the 1980s, the new head hypothesis proposed that the vertebrate head is an evolutionary novelty resulting from the emergence of neural crest and cranial placodes (thickened areas of ectoderm). However, in 2014, a transient larva tissue of the lancelet was found to be virtually indistinguishable from the neural crest-derived cartilage which forms the vertebrate skull, suggesting that persistence of this tissue and expansion into the entire head space could be a viable evolutionary route to formation of the vertebrate head. For laysummary see: Advanced vertebrates have increasingly elaborate brains.

The human inner ear develops during week 4 of embryonic development from the auditory placode, a thickening of the ectoderm which gives rise to the bipolar neurons of the cochlear and vestibular ganglions. As the auditory placode invaginates towards the embryonic mesoderm, it forms the auditory vesicle or otocyst. The auditory vesicle will give rise to the utricular and saccular components of the membranous labyrinth. They contain the sensory hair cells and otoliths of the macula of utricle and of the saccule, respectively, which respond to linear acceleration and the force of gravity.

1 - morula, 2 - blastula 1 - blastula, 2 - gastrula with blastopore; orange - ectoderm, red - endoderm Embryology (from Greek ἔμβρυον, embryon, "the unborn, embryo"; and -λογία, -logia) is the branch of biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology. Early embryology was proposed by Marcello Malpighi, and known as preformationism, the theory that organisms develop from pre-existing miniature versions of themselves. Then Aristotle proposed the theory that is now accepted, epigenesis.

The effects and influences of RE1/NRSE and REST/NRSF are significant in non-neuronal cells that require the repression or silencing of neuronal genes. These silencer elements also regulate the expression of genes that do not induce neuron- specific proteins and studies have shown the extensive impact these factors have in cellular processes. In Xenopus laevis, RE1/NRSE and REST/NRSF dysfunction or mutation demonstrated significant impact on neural tube, cranial ganglia, and eye development. All of these alterations can be traced to an improper patterning of the ectoderm during Xenopus development.

During normal development, cutaneous ectoderm separates from neuroectoderm to allow for the insertion of mesoderm. That is, the skin separates from the tissue of the spinal cord to allow proper formation of the vertebral column. In cases of congenital dermal sinus there is a failure in this process, resulting in formation of a persistent connection between the skin and neural tissue. This manifests as a tract extending from the surface of the skin to the spinal cord lined with stratified squamous epithelium, surrounded by dermal and neurological tissue.

Neural crest was first described in the chick embryo by Wilhelm His Sr. in 1868 as "the cord in between" (Zwischenstrang) because of its origin between the neural plate and non-neural ectoderm. He named the tissue ganglionic crest since its final destination was each lateral side of the neural tube where it differentiated into spinal ganglia. During the first half of the 20th century the majority of research on neural crest was done using amphibian embryos which was reviewed by Hörstadius (1950) in a well known monograph.Hörstadius, S. (1950).

For her dissertation work at Radcliffe, Reddick studied neurodevelopment of the chick medulla. For these experiments, she used embryos from Plymouth Rock chickens. The goal of her experiments was to understand how much of that area of the brain was already determined and how much was dependent on interactions with surrounding developing tissues, such as notochord, somites, and ectoderm. The results of these experiments supported the hypothesis that while some aspects of the post-otic medulla in chick have already been determined, there needs to be a continuous interaction with surrounding developing tissues.

During organogenesis, molecular and cellular interactions prompt certain populations of cells from the different germ layers to differentiate into organ-specific cell types. For example, in neurogenesis, a subpopulation of cells from the ectoderm segregate from other cells and further specialize to become the brain, spinal cord, or peripheral nerves. The embryonic period varies from species to species. In human development, the term fetus is used instead of embryo after the ninth week after conception, whereas in zebrafish, embryonic development is considered finished when a bone called the cleithrum becomes visible.

The central nervous system (CNS) is derived from the ectoderm—the outermost tissue layer of the embryo. In the third week of human embryonic development the neuroectoderm appears and forms the neural plate along the dorsal side of the embryo. The neural plate is the source of the majority of neurons and glial cells of the CNS. A groove forms along the long axis of the neural plate and, by week four of development, the neural plate wraps in on itself to give rise to the neural tube, which is filled with cerebrospinal fluid (CSF).

The embryoblast forms an embryonic disc, which is a bilaminar disc of two layers, an upper layer called the epiblast (primitive ectoderm) and a lower layer called the hypoblast (primitive endoderm). The disc is stretched between what will become the amniotic cavity and the yolk sac. The epiblast is adjacent to the trophoblast and made of columnar cells; the hypoblast is closest to the blastocyst cavity and made of cuboidal cells. The epiblast migrates away from the trophoblast downwards, forming the amniotic cavity, the lining of which is formed from amnioblasts developed from the epiblast.

Overview of iPS cells Creating induced pluripotent stem cells ("iPSCs") is a long and inefficient process. Pluripotency refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous tissue). A specific set of genes, often called "reprogramming factors", are introduced into a specific adult cell type. These factors send signals in the mature cell that cause the cell to become a pluripotent stem cell.

The epithelium in all animals is derived from the ectoderm and endoderm, with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, and the digestive tract. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina.

During differentiation, pluripotent cells make a number of developmental decisions to generate first the three germ layers (ectoderm, mesoderm and endoderm) of the embryo and intermediate progenitors, followed by subsequent decisions or check points, giving rise to all the body's mature tissues. The differentiation process can be modeled as sequence of binary decisions based on probabilistic or stochastic models. Developmental biology and embryology provides the basic knowledge of the cell types' differentiation through mutation analysis, lineage tracing, embryo micro-manipulation and gene expression studies. Cell differentiation and tissue organogenesis involve a limited set of developmental signaling pathways.

The mesoglea can contain skeletal elements derived from cells migrated from ectoderm. The sac-like body built up in this way is attached usually to some firm object by its blind end, and bears at the upper end the mouth which is surrounded by a circle of tentacles which resemble glove fingers. The tentacles are organs which serve both for the tactile sense and for the capture of food. Polyps extend their tentacles, particularly at night, containing coiled stinging nettle-like cells or nematocysts which pierce and poison and firmly hold living prey paralysing or killing them.

The four vegetal blastomeres divide equatorially but unequally and they give rise to four big macromeres and four smaller micromeres. Once this fourth division has occurred, the embryo has reached a 16 cell stage. P. flava has a 16 cell embryo with four vegetal micromeres, eight animal mesomeres and 4 larger macromeres. Further divisions occur until P. flava finishes the blastula stage and goes on to gastrulation. The animal mesomeres of P. flava go on to give rise to the larva’s ectoderm, animal blastomeres also appear to give rise to these structures though the exact contribution varies from embryo to embryo.

Without the presence of Rab11FIP5, it is hypothesized that the internalized AMPA receptors cannot be recycled back onto the plasma membrane because the receptors cannot be correctly trafficked to intracellular organelles responsible for recycling. Rab11FIP5 has also been implicated as a protein involved in the creation of tissue polarity during development. Rab11FIP5 has been shown to be involved in the vesicle trafficking and degradation of proteins used to coordinate embryonic development. This is conducted in a manner that helps maintain the ectoderm polarity in embryonic Drosophila. Rab11FIP5 is also suggested to be involved in aiding salivary epithelial cells to adjust to extracellular pH.

Applying the process on a genome-wide scale can then allow us to detect patterns of founder genes births and infer the role of certain genes involved in clade-specific developmental processes and physiological pathways, and the origin of those traits. The developers of the method gave in the original paper an example how to exploit this system in practice using Drosophila. They gathered 13,000 genes for which they determined the founder genes, regrouping them in their respective phylostrata. They also segregated the families of genes depending on whether they were mainly expressed in either of the three germ layers (endoderm, mesoderm, ectoderm).

FoxI1e mRNA is expressed zygotically (stage 8.5) and reaches higher level of expression early in gastrulation and maintains that level in neurula, tailbud until early tadpole stages. FoxI1e has a peculiar mosaic expression pattern, it is expressed first in the dorsal ectoderm and while gastrula progresses, the expression goes through the ventral side and its expression is down- regulated in the dorsal side when the neural plate is forming.Mir, A., Kofron, M., Heasman, J., Mogle, M., Lang, S., Birsoy, B., and Wylie, C. (2008). Long- and short-range signals control the dynamic expression of an animal hemisphere-specific gene in Xenopus.

In mammalian embryogenesis, differentiation and segregation of cells composing the inner cell mass of the blastocyst yields two distinct layers—the epiblast ("primitive ectoderm") and the hypoblast ("primitive endoderm"). While the cuboidal hypoblast cells delaminate ventrally, away from the embryonic pole, to line the blastocoele, the remaining cells of the inner cell mass, situated between the hypoblast and the polar trophoblast, become the epiblast and comprise columnar cells. In the mouse, primordial germ cells are specified from epiblast cells. This specification is accompanied by extensive epigenetic reprogramming that involves global DNA demethylation, chromatin reorganization and imprint erasure leading to totipotency.

The region where the crescentic masses of the ectoderm and endoderm come into direct contact with each other constitutes a thin membrane, the buccopharyngeal membrane (or oropharyngeal membrane), which forms a septum between the primitive mouth and pharynx. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is afterward developed, and this region is therefore designated the pericardial area. The buccopharyngeal membranes serve as a respiratory surface in a wide variety of amphibians and reptiles. In this type of respiration, membranes in the mouth and throat are permeable to oxygen and carbon dioxide.

The polyps sit in cup- shaped depressions in the skeleton known as corallites. Colonies of stony coral are very variable in appearance; a single species may adopt an encrusting, plate-like, bushy, columnar or massive solid structure, the various forms often being linked to different types of habitat, with variations in light level and water movement being significant. The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of cells. The outer layer is known technically as the ectoderm, the inner layer as the endoderm.

The extension of the mesoderm takes place throughout the whole of the embryonic and extra-embryonic areas of the ovum, except in certain regions. One of these is seen immediately in front of the neural tube. Here the mesoderm extends forward in the form of two crescentic masses, which meet in the middle line so as to enclose behind them an area that is devoid of mesoderm. Over this area, the ectoderm and endoderm come into direct contact with each other and constitute a thin membrane, the buccopharyngeal membrane, which forms a septum between the primitive mouth and pharynx.

In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is afterward developed, and this region is therefore designated the pericardial area. A second region where the mesoderm is absent, at least for a time, is that immediately in front of the pericardial area. This is termed the proamniotic area, and is the region where the proamnion is developed; in humans, however, it appears that a proamnion is never formed. A third region is at the hind end of the embryo, where the ectoderm and endoderm come into apposition and form the cloacal membrane.

Several Wnts, including Wnt6, have shown to be involved in the formation of the ventral body wall and when inhibited result in birth defects such as failure of the wall to close, hypoplasia of the musculature, and other defects. Following the formation of the somites from the Paraxial Mesoderm, the outermost cells of the somites undergo a mesenchymal to epithelial transition. Wnt6 is expressed by the overlying ectoderm and promotes the production of Paraxis, which facilitates the transition. While many structures will still form if Wnt6 is knocked out, the structures (ribs, vertebra, and muscles) are fused and not organized properly.

The ectoderm contributes to the formation of many parts of the body, including the skin, sweat glands, hair, teeth, and nails. During embryonic development, these and/or other parts of the baby's body, including the lens of the eye, parts of the inner ear, the fingers and toes, or nerves, among others, may fail to develop normally. When a child has at least two types of abnormal ectodermal features—for example, malformed teeth and extremely sparse hair—the child is identified as being affected by an ED "syndrome." Each of the roughly 150 ED syndromes represents a different combination of abnormalities.

In mammalian embryogenesis, differentiation and segregation of cells in the inner cell mass of the blastocyst produces two different layers—the epiblast ("primitive ectoderm") and the hypoblast ("primitive endoderm"). The first segregation of cells within the inner cell mass forms two layers. In contact with the blastocoel, the lower layer is called the primitive endoderm, and it is homologous to the chick embryo hypoblast. While hypoblast cells delaminate ventrally, away from the embryonic pole, to line the blastocoele, the remaining cells of the inner cell mass, situated between the hypoblast and the polar trophoblast, become the epiblast.

The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation. The ear develops from the first pharyngeal pouch and six small swellings that develop in the early embryo called otic placodes, which are derived from ectoderm.

This Xist RNA is also probably bound by EHMT2 which inserts a histone 3 lysine 9 trimethylation mark, another indicator of repression. EeD (embryonic ectoderm development: a core subunit of PRC2) specifically recognizes and binds to the repressive trimethylated lysine marks, contributing to the affinity of PRC2 for nucleosomes. PRC2 recruits DNMT3, which can add the 5 methyl DNA mark to CpG islands. Histone 3 lysine 27 trimethylation is then bound by PRC1 to trigger H2A ubiqination. Condensation continues with these marks as histone 3 lysine 4 is demethylated and histone 3 lysine 9 is deacetylated.

The adrenal medulla is derived from neural crest cells, which come from the ectoderm layer of the embryo. These cells migrate from their initial position and aggregate in the vicinity of the dorsal aorta, a primitive blood vessel, which activates the differentiation of these cells through the release of proteins known as BMPs. These cells then undergo a second migration from the dorsal aorta to form the adrenal medulla and other organs of the sympathetic nervous system. Cells of the adrenal medulla are called chromaffin cells because they contain granules that stain with chromium salts, a characteristic not present in all sympathetic organs.

This opening is hidden beneath a protective bony cover called the operculum. Juvenile bichirs have external gills, a very primitive feature that they share with larval amphibians. Previously, the evolution of gills was thought to have occurred through two diverging lines: gills formed from the endoderm, as seen in jawless fish species, or those form by the ectoderm, as seen in jawed fish. However, recent studies on gill formation of the little skate (Leucoraja erinacea) has shown potential evidence supporting the claim that gills from all current fish species have in fact evolved from a common ancestor.

Reddick began her embryogenesis studies using the developing chicken embryo, specifically White Leghorns and Rhode Island Reds. The larger question she addressed was what the developmental potential was of portions of the early chick blastoderm, when transplanted to the chorioallantoic membrane of a chick in a later stage of development, in “cut-and-paste” experiments. These “cut-and-paste” experiments supported the hypothesis that the node is necessary and sufficient for specifying differentiation of many derivatives of ectoderm, mesoderm, and endoderm, but not all. For instance, any cases of liver tissue development that she observed only occurred where there was heart tissue nearby.

The three tissue layers give rise to the pharyngeal apparatus, formed by six pairs of pharyngeal arches, a set of pharyngeal pouches and pharyngeal grooves, which are the most typical feature in development of the head and neck. The formation of each region of the face and neck is due to the migration of the neural crest cells which come from the ectoderm. These cells determine the future structure to develop in each pharyngeal arch. Eventually, they also form the neurectoderm, which forms the forebrain, midbrain and hindbrain, cartilage, bone, dentin, tendon, dermis, pia mater and arachnoid mater, sensory neurons, and glandular stroma.

This is principally because the primordium of the cranium during the period of fetal brain development is not yet ossified (hardened into bone through calcification). The tissue covering the embryonic cerebral cortex is several thin layers of ectoderm (future skin) and mesenchyme (future muscle and connective tissue, including the future cranium). These thin layers grow easily along with cortical expansion but eventually the cranial mesenchyme differentiates into cartilage; ossification of the cranial plates does not occur until later in development. The human cranium continues to grow substantially along with the brain after birth until the cranial plates finally fuse after several years.

Subsequent differentiation proceeds to form derivatives of the three germ lineages. In the absence of supplements, the “default” differentiation of ESCs is largely toward ectoderm, and subsequent neural lineages. However, alternative media compositions, including the use of fetal bovine serum as well as defined growth factor additives, have been developed to promote the differentiation toward mesoderm and endoderm lineages. As a result of the three-dimensional EB structure, complex morphogenesis occurs during EB differentiation, including the appearance of both epithelial- and mesenchymal- like cell populations, as well as the appearance of markers associated with the epithelial-mesenchymal transition (EMT).

These cells are held together by cadherins (specifically E and N-cadherin), types of intercellular binding protein. When the cells at the peaks of the neural folds come in proximity with each other, it is the affinity for similar cadherin molecules (N-cadherins) that allows these cells to bind to each other. Thus, when the neural tube precursor cells begin expressing N-cadherin in the place of E-cadherin, this causes the neural tube to form and separate from the ectoderm and settle inside the embryo. When the cells fail to associate in a manner that is not part of the normal course of development, severe diseases can occur.

Only cells expressing the same kind of cadherin can bind to each other; since the peaks of the neural folds both express N-cadherin, they are able to merge into a continuous sheet of cells. Likewise, it is this diminished affinity between cells expressing different types of cadherin that allows the neural tube precursor cells to separate from the ectoderm, forming the neural tube on the interior of the embryo and the true epidermis on the exterior. Another set of molecules involved with the merging of the neural folds are the ephrin molecules and their Eph receptors, which adhere in a similar manner to the cadherin molecules discussed above.

In a developing embryo a gradient of retinoic acid aids in the combinatorial patterns of Hox gene expression along the body axis, which causes regions of the paraxial mesoderm to emit a signal to the lateral mesoderm that causes the expression of Tbx4 and Tbx5. When these two molecules are expressed that stimulate the secretion of FGF-10, which will induce the ectoderm to produce FGF-8. FGF-8 and FGF-10 together promote limb development. Mutations or teratogens that interfere with Tbx4/Tbx5 or FGF-8/FGF-10 has the ability to cause a child to be born without one or more limbs.

The establishment of the dorsal-ventral axis during early embryological development has also been extensively studied in C. teleta. It is reported that micromere 2d, a cell that is born when the embryo has 16 cells, has organizing activity which enables it to induce dorsal-ventral polarity within the embryo. Fate map studies have demonstrated that cell 2d gives rise to ectoderm in the larval trunk and pygidium in C. teleta, while descendants of the first quartet micromeres give rise to structures in the larval head. When micromere 2d is laser ablated, 2d derived structures as well as dorsal-ventral organization in the head is lost.

The exact cause of the condition is unknown. Although various theories indicate incomplete separation of monozygotic twins as an etiological factor, abnormal adherence between the ectoderm and endoderm during gastrulation, polytopic primary developmental field defects, somatic and germ line mutations in developmental genes, and damage to the caudal cell mass and posterior gut have also been linked to cause structural anomalies in the caudal region. It is speculated that the condition is related to the HOX gene, namely HOX10 and HOX11. Normally coding for the mammalian appendicular and axial skeleton, misexpression of the genetic factors could lead to abnormal proliferation of the caudal mesenchyme.

Limb development in vertebrates is an area of active research in both developmental and evolutionary biology, with much of the latter work focused on the transition from fin to limb. Limb formation begins in the morphogenetic limb field, as mesenchymal cells from the lateral plate mesoderm proliferate to the point that they cause the ectoderm above to bulge out, forming a limb bud. Fibroblast growth factor (FGF) induces the formation of an organizer at the end of the limb bud, called the apical ectodermal ridge (AER), which guides further development and controls cell death. Programmed cell death is necessary to eliminate webbing between digits.

The lateral plate mesodermal cells secrete fibroblast growth factors (FGF7 and FGF10) to induce the overlying ectoderm to form an organizer at the end of the limb bud, called the apical ectodermal ridge (AER), which guides further development and controls cell death. The AER secretes further growth factors FGF8 and FGF4 which maintain the FGF10 signal and induce proliferation in the mesoderm. The position of FGF10 expression is regulated by two Wnt signaling pathways: Wnt8c in the hindlimb and Wnt2b in the forelimb. The forelimb and the hindlimb are specified by their position along the anterior/posterior axis and possibly by two transcription factors: Tbx5 and Tbx4, respectively.

The specification of primordial germ cells in mammals is mainly attributed to the downstream functions of two signaling pathways; the BMP signaling pathway and the canonical WNT/β-catenin pathway. Bone morphogenetic protein 4 (BMP4) is released by the extra-embryonic ectoderm (ExE) at embryonic day 5.5 to 5.75 directly adjacent to the epiblast and causes the region of the epiblast nearest to the ExE to express Blimp1 and Prdm14 in a dose-dependent manner. This is evident as the number of PGCs forming in the epiblast decreases in proportion to the loss of BMP4 alleles. BMP4 acts through its downstream intercellular transcription factors SMAD1 and SMAD5.

As neurulation proceeds after induction the cells of the neural plate become high-columnar and can be identified through microscopy as different from the surrounding presumptive epithelial ectoderm (epiblastic endoderm in amniotes). The cells move laterally and away from the central axis and change into a truncated pyramid shape. This pyramid shape is achieved through tubulin and actin in the apical portion of the cell which constricts as they move. The variation in cell shapes is partially determined by the location of the nucleus within the cell, causing bulging in areas of the cells forcing the height and shape of the cell to change.

Mouse skull All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics; a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal arches; and a tail posterior to the anus. The spinal cord is protected by the vertebral column and is above the notochord and the gastrointestinal tract is below it. Nervous tissue is derived from the ectoderm, connective tissues are derived from mesoderm, and gut is derived from the endoderm. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut.

Expression is first seen in the forebrain, hindbrain, head ectoderm and spinal cord followed by later expression in midbrain. This transcription factor is most noted for its use in the interspecifically induced expression of ectopic eyes and is of medical importance because heterozygous mutants produce a wide spectrum of ocular defects such as aniridia in humans. Pax6 serves as a regulator in the coordination and pattern formation required for differentiation and proliferation to successfully take place, ensuring that the processes of neurogenesis and oculogenesis are carried out successfully. As a transcription factor, Pax6 acts at the molecular level in the signaling and formation of the central nervous system.

Thus, a mutation or alteration in either the silencing region RE1/NRSE or silencer REST/NRSF factor can disrupt the proper differentiation and specification of the neuroepithelial domain and also hinder the formation of skin or ectoderm. The lack of these factors result in a decreased production of bone morphogenetic protein (BMP), which translates into a deficient development of the neural crest. Hence, the effects of NRSE and NRSF are of fundamental importance for neurogenesis of the developing embryo, and also in the early stages of ectodermal patterning. Ultimately, inadequate functioning of these factors can result in aberrant neural tube, cranial ganglia, and eye development in Xenopus.

The development of the pronephric duct is a part of the development of the urinary system, and the development of the reproductive system. In the outer part of the intermediate mesoderm, immediately under the ectoderm, in the region from the fifth cervical segment to the third thoracic segment, a series of short evaginations from each segment grows dorsally and extends caudally, fusing successively from before backward to form the pronephric duct. This continues to grow caudalward until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the mesonephric duct. Thus, the mesonephric duct remains after the atrophy of the pronephros.

Epiboly in zebrafish is the first coordinated cell movement, and begins once the embryo has completed the blastula stage. At this point the zebrafish embryo contains three portions: an epithelial monolayer known as the enveloping layer (EVL), a yolk syncytial layer (YSL) which is a membrane-enclosed group of nuclei that lie on top of the yolk cell, and the deep cells (DEL) of the blastoderm which will eventually form the embryo's three germ layers (ectoderm, mesoderm, and endoderm). The EVL, YSL, and DEL all undergo epiboly. 222x222pxCartoon of a 4-hour post fertilization zebrafish embryo, before the initiation of epiboly Radial intercalation occurs in the DEL.

During development: Throughout development, the spatial and temporal expression of pcsk6 regulates embryogenesis by activating TGFβ related differentiation factors, which include BMP and Nodal. Elevated levels of Pcsk6 was detected in maternal decidual cells of the implantation site and the extraembryonic ectoderm. The regulation of proper gradient of Nodal and BMPs is crucial for gastrulation, proximal-distal axis, and establishment of left-right axis patterning. Developmental Pcsk6 knockout studies found that mice embryos that lack Pcsk6 develop heterotaxia, left pulmonary isomerism, and/or craniofacial malformations due to disruption in specification of anterior-posterior and left-right axis that resulted from the dysregulation of Nodal and BMP signaling.

Once neurons have positioned themselves, their axons sprout and navigate through the brain, branching and extending as they go, until the tips reach their targets and form synaptic connections. In a number of parts of the nervous system, neurons and synapses are produced in excessive numbers during the early stages, and then the unneeded ones are pruned away. For vertebrates, the early stages of neural development are similar across all species. As the embryo transforms from a round blob of cells into a wormlike structure, a narrow strip of ectoderm running along the midline of the back is induced to become the neural plate, the precursor of the nervous system.

A cyst is a pathological epithelial lined cavity that fills with fluid or soft material and usually grows from internal pressure generated by fluid being drawn into the cavity from osmosis (hydrostatic pressure). The bones of the jaws, the mandible and maxilla, are the bones with the highest prevalence of cysts in the human body. This is due to the abundant amount of epithelial remnants that can be left in the bones of the jaws. The enamel of teeth is formed from ectoderm (the precursor germ layer to skin and mucosa), and so remnants of epithelium can be left in the bone during odontogenesis (tooth development).

12: 167-178 In mouse models, Mafb mRNA and protein were detected in both craniofacial ectoderm and neural crest-derived mesoderm between embryonic days 13.5 and 14.5; expression was strong in the epithelium around the palatal shelves and in the medial edge epithelium during palatal fusion. After fusion, Mafb expression was stronger in oral epithelium compared to mesenchymal tissue. In addition, sequencing analysis detected a new missense mutation in the Filipino population, H131Q, that was significantly more frequent in cases than in matched controls. The gene-poor regions either side of the MAFB gene include numerous binding sites for transcription factors that are known to have a role in palate development.

The rest of the Hydra is known as the column and is divided into four sections: the gastric section (between the tentacles and first bud), budding section (which produces the buds), the peduncle (between the lowest bud and basal disc), and the basal disc (foot- like structure). Hydra are diploblastic organisms, the body is composed of two embryonic cell layers; the ectoderm and the endoderm. The endoderm lines the gastrovascular cavity, which is a water-filled sac, this acts as a hydroskeleton and site for food digestion. They also have a simple nervous system that consist of a nerve net that covers the entire body.

In the fourth week the somites lose their organization and cover the notochord and spinal cord to form the backbone. In the fifth week, there are 4 occipital somites, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 8 to 10 coccygeal that will form the axial skeleton. Somitic derivatives are determined by local signaling between adjacent embryonic tissues, in particular the neural tube, notochord, surface ectoderm and the somitic compartments themselves. The correct specification of the deriving tissues, skeletal, cartilage, endothelia and connective tissue is achieved by a sequence of morphogenic changes of the paraxial mesoderm, leading to the three transitory somitic compartments: dermomyotome, myotome and sclerotome.

The rostral neuropore or anterior neuropore is a region corresponding to the opening of the embryonic neural tube in the anterior portion of the developing prosencephalon. The central nervous system develops from the neural tube, which initially starts as a plate of cells in the ectoderm and this is called the neural plate, the neural plate then undergoes folding and starts closing from the center of the developing fetus, this leads to two open ends, one situated cranially/rostrally and the other caudally. Bending of the neural plate begins on day 22,Human Embryology, 4th edition, PA and the cranial neuropore closes on day 24.O'Rahilly R, Müller F. Bidirectional closure of the rostral neuropore in the human embryo].

The rhomboid proteases – the first known intramembranous serine proteasesFreeman M (2009) Rhomboids: 7 years of a new protease family. Semin Cell Dev Biol 20(2):231–239 – were discovered in 1988.Mayer U, Nüsslein-Volhard C (1988) A group of genes required for pattern formation in the ventral ectoderm of the Drosophila embryo. Genes Dev. 1988 Nov;2(11):1496–511 The first rhomboid protease was cloned in 1990Bier E, Jan LY, Jan YN (1990) Rhomboid, a gene required for dorsoventral axis establishment and peripheral nervous system development in Drosophila melanogaster. Genes Dev 4(2):190–203 Rhomboid proteases have a core of six transmembrane helices with the active site residues lying in a hydrophilic cavity.

Stem cells resembling totipotent blastomeres from 2-cell stage embryos can arise spontaneously in mouse embryonic stem cell cultures and also can be induced to arise more frequently in vitro through down-regulation of the chromatin assembly activity of CAF-1. The human development model is one which can be used to describe how totipotent cells arise. Human development begins when a sperm fertilizes an egg and the resulting fertilized egg creates a single totipotent cell, a zygote. In the first hours after fertilization, this zygote divides into identical totipotent cells, which can later develop into any of the three germ layers of a human (endoderm, mesoderm, or ectoderm), or into cells of the placenta (cytotrophoblast or syncytiotrophoblast).

Example: American psychologist William Herbert Sheldon associates body types with human temperament types.Sheldon proposed that the human physique be classed according to the relative contribution of three fundamental elements, somatotypes, named after the three germ layers of embryonic development: the endoderm, (develops into the digestive tract), the mesoderm, (becomes muscle, heart and blood vessels), and the ectoderm (forms the skin and nervous system). Sheldon's "somatotypes" and their supposed associated physical traits can be summarized as follows: Ectomorphic: characterized by long and thin muscles/limbs and low fat storage; receding chin, usually referred to as slim. Mesomorphic: characterized by medium bones, solid torso, low fat levels, wide shoulders with a narrow waist; usually referred to as muscular.

The basic structure of the reproductive tract is similar in both sexes, with a mesodermal gonoduct (sperm duct or oviduct) emerging from both sides of the U-shaped gonad (testis or ovary). The two gonoducts fuse into a single duct, which leads into a cuticle-lined duct derived from the ectoderm into the open through an organ (penis in males or ovipositor in females) that can be everted through a combination of muscles and hemolymph pressure. These eversible organs play an important role in determining taxonomic relationships. The penis is often complex, consisting of a long shaft and a shorter glans at the end, which is often equipped with various projections such as spines.

Immature, or solid, teratomas are the most common type of ovarian germ cell tumor, making up 40–50% of cases. Teratomas are characterized by the presence of disorganized tissues arising from all three embryonic germ layers: ectoderm, mesoderm, and endoderm; immature teratomas also have undifferentiated stem cells that make them more malignant than mature teratomas (dermoid cysts). The different tissues are visible on gross pathology and often include bone, cartilage, hair, mucus, or sebum, but these tissues are not visible from the outside, which appears to be a solid mass with lobes and cysts. Histologically, they have large amounts of neuroectoderm organized into sheets and tubules along with glia; the amount of neural tissue determines the histologic grade.

A small percentage of cases result from spontaneous new mutations in the gene, where there is no family history of the condition. The neural crest is a group of temporary migratory cells that are left over after the neural tube has closed (neurulation), around the fourth week of embryonic development. They are responsible for differentiating into a diverse group of cells that reach different areas of the body. The neural tube and neural crest are derived from the ectoderm; the neural tube goes on to form the brain and spinal cord, while the neural crest cells eventually go on to form various bones and cartilage of the skull and face by migrating through the pharyngeal arches.

There is a complex sequence of events that result in a well formed heart at birth and disruption of any portion may result in a defect. The orderly timing of cell growth, cell migration, and programmed cell death ("apoptosis") has been studied extensively and the genes that control the process are being elucidated. Around day 15 of development, the cells that will become the heart exist in two horseshoe shaped bands of the middle tissue layer (mesoderm), and some cells migrate from a portion of the outer layer (ectoderm), the neural crest, which is the source of a variety of cells found throughout the body. On day 19 of development, a pair of vascular elements, the "endocardial tubes", form.

Fruitflies lacking the PAX6 gene have no eyes PAX6 is a member of the Pax gene family which is responsible for carrying the genetic information that will encode the Pax-6 protein. It acts as a "master control" gene for the development of eyes and other sensory organs, certain neural and epidermal tissues as well as other homologous structures, usually derived from ectodermal tissues. However, it has been recognized that a suite of genes is necessary for eye development, and therefore the term of "master control" gene may be inaccurate. Pax-6 is expressed as a transcription factor when neural ectoderm receives a combination of weak Sonic hedgehog (SHH) and strong TGF- Beta signaling gradients.

EZH2 function is highly dependent upon its recruitment by the PRC2 complex. In particular, WD40-repeat protein embryonic ectoderm development (EED) and zinc finger protein suppressor of zeste 12 (SUZ12) are needed to stabilize the interaction of EZH2 with its histone substrate Recently, two isoforms of EZH2 generated from alternative splicing have been identified in humans: EZH2α and EZH2β. Both isoforms contain elements that have been identified as important for EZH2 function including the nuclear localization signal, the EED and SUZ12 binding sites as well as the conserved SET domain. Most studies have thus far focused on the longer isoform EZH2α, but EZH2β, which lacks exons 4 and 8, has been shown to be active.

Based on the similarities between lens and cornea, such as abundant water-soluble enzymes, and being derived from ectoderm, the lens and cornea are thought to be co-evolved as a "refraction unit." Gene sharing would maximize light transmission and refraction to the retina by this refraction unit. Studies have shown that many water-soluble enzymes/proteins expressed by cornea are identical to taxon-specific lens crystallins, such as ALDH1A1/ η-crystallin, α-enolase/τ-crystallin, and lactic dehydrogenase/ -crystallin. Also, the anuran corneal epithelium, which can transdifferentiate to regenerate the lens, abundantly expresses ubiquitous lens crystallins, α, β and γ, in addition to the taxon-specific crystallin α-enolase/τ-crystallin.

First, extracellular signaling molecules, secreted from the adjacent epidermis and underlying mesoderm such as Wnts, BMPs and Fgfs separate the non-neural ectoderm (epidermis) from the neural plate during neural induction. Wnt signaling has been demonstrated in neural crest induction in several species through gain-of-function and loss-of- function experiments. In coherence with this observation, the promoter region of slug (a neural crest specific gene) contains a binding site for transcription factors involved in the activation of Wnt-dependent target genes, suggestive of a direct role of Wnt signaling in neural crest specification. The current role of BMP in neural crest formation is associated with the induction of the neural plate.

Cell grafting in the early stages of embryo development has provided crucial information on cell fates and the processes of determination. Grafting at specific stages of neurulation has advanced research on the signaling necessary for the proper development of the neural plate and other structures. The grafting of the ectoderm and neural structures is very specialized and delicate procedure, requiring the removal and marking of a desired group of cells, followed by their transplantation, for example, into a new area of the embryo. Grafting experiments done in Xenopus and chicken embryos show the neural plate's capability to induce other regions of cells, including the pre-placodal region, a group of ectodermal cells essential to the function of sensory organs.

Development of the neural tube During the third week of embryonic growth the brain begins to develop in the early fetus in a process called morphogenesis. Neuroepithelial cells of the ectoderm begin multiplying rapidly and fold in forming the neural plate, which invaginates during the fourth week of embryonic growth and forms the neural tube. The formation of the neural tube polarizes the neuroepithelial cells by orienting the apical side of the cell to face inward, which later becomes the ventricular zone, and the basal side is oriented outward, which contacts the pial, or outer surface of the developing brain. As part of this polarity, neuroepithelial cells express prominin-1 in the apical plasma membrane as well as tight junctions to maintain the cell polarity.

Somatotype is a taxonomy developed in the 1940s by American psychologist William Herbert Sheldon to categorize the human physique according to the relative contribution of three fundamental elements which he termed 'somatotypes', classified by him as 'ectomorphic', 'mesomorphic' and 'endomorphic'. He named these after the three germ layers of embryonic development: the endoderm, (which develops into the digestive tract), the mesoderm, (which becomes muscle, heart and blood vessels) and the ectoderm (which forms the skin and nervous system). Later variations of the method, developed by his original research assistant Barbara Heath, and later Lindsay Carter and Rob Rempel are still in occasional academic use. Constitutional psychology is a theory developed by Sheldon in the 1940s, which attempted to associate his somatotype classifications with human temperament types.

Wnt signalling from adjacent tissues has been shown to induce cells in somites that receive these Wnt signals to express Pax3 and Pax7 in addition to myogenic regulatory factors, including Myf5 and MyoD. Specifically, Wnt3a can directly induce MyoD expression via cis-element interactions with a distal enhancer and Wnt response element.. Wnt1 from dorsal neural tube and Wnt6/Wnt7a from surface ectoderm have also been implicated in promoting myogenesis in the somite; the latter signals may act primarily through Myod. In typical adult muscles in a resting condition (absence of physiological stress) the specific Wnt family proteins that are expressed are Wnt5a, Wnt5b, Wnt7a and Wnt4. When a muscle becomes injured (thus requiring regeneration) Wnt5a, Wnt5b, and Wnt7a are increased in expression.

The cells of the inner cell mass (embryoblast), which are known as human embryonic stem cells (hESCs), will further differentiate to form four structures: the amnion, the yolk sac, the allantois, and the embryo itself. Human embryonic stem cells are pluripotent, that is, they can differentiate into any of the cell types present in the adult human, and into any of the intermediate progenitor cell types that eventually turn into the adult cell lines. hESCs are also immortal, in that they can divide and grow in number indefinitely, without undergoing either differentiation or cellular aging (cellular senescence). The first differentiation of the hESCs that form the embryo proper, is into three cell types known as the germ layers: the ectoderm, the mesoderm, and the endoderm.

It forms the epithelial lining of the whole of the digestive tract except part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tract, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and alveoli of the lungs; the bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus. The endoderm forms: the pharynx, the esophagus, the stomach, the small intestine, the colon, the liver, the pancreas, the bladder, the epithelial parts of the trachea and bronchi, the lungs, the thyroid, and the parathyroid.

PAX6 is essential is the formation of the retina, lens and cornea due to its role in early cell determination when forming precursors of these structures such as the optic vesicle and overlying surface ectoderm. PAX10 mutations also hinder nasal cavity development due to the similar precursor structures that in small eye mice do not express PAX10 mRNA. Mice lacking any functional pax6 begin to be phenotypically differentiable from normal mouse embryos at about day 9 to 10 of gestation. The full elucidation of the precise mechanisms and molecular components by which the PAX6 gene influences eye, nasal and central nervous system development are still researched however, the study of PAX6 has brought more understanding to the development and genetic complexities of these mammalian body systems.

The DIO3 gene codes for type 3 iodothyronine deiodinase (D3), an enzyme that inactivates thyroid hormones and is highly expressed throughout fetal development, peaking early and decreasing towards the end of gestation. Part of the DLK1-Dio3 imprinting control region, this gene is one involved in the epigenetic process that causes a subset of genes to be regulated based on their parental origin . Such imprinted genes are required for the formation of the placenta as well as the development of cellular lineages such as those derived from the mesoderm and ectoderm. D3 is found in the pregnant uterus, placenta, and mammalian fetal tissues where it is thought to be involved in the transfer of thyroid hormone between the mother and fetus.

Kuijk, et al Validation of reference genes for quantitative RT-PCR studies in porcine oocytes and preimplantation embryos BMC Developmental Biology 2007, 7:58 doi:10.1186/1471-213X-7-58 The ICM and the TE will generate distinctly different cell types as implantation starts and embryogenesis continues. Trophectoderm cells form extraembryonic tissues, which act in a supporting role for the embryo proper. Furthermore, these cells pump fluid into the interior of the blastocyst, causing the formation of a polarized blastocyst with the ICM attached to the trophectoderm at one end (see figure). This difference in cellular localization causes the ICM cells exposed to the fluid cavity to adopt a primitive endoderm (or hypoblast) fate, while the remaining cells adopt a primitive ectoderm (or epiblast) fate.

For example, the ectoderm will give rise to the skin epidermis and the nervous system, the mesoderm will give rise to the vascular system, muscles, bone, and connective tissues, and the endoderm will give rise to organs of the digestive system and epithelium of the digestive system and respiratory system. Many visible changes in embryonic structure happen throughout gastrulation as the cells that make up the different germ layers migrate and cause the previously round embryo to fold or invaginate into a cup-like appearance. Past gastrulation, an embryo continues to develop into a mature multicellular organism by forming structures necessary for life outside of the womb or egg. As the name suggests, organogenesis is the stage of embryonic development when organs form.

Before the neural groove is closed a ridge of ectodermal cells appears along the prominent margin of each neural fold; this is termed the neural crest or ganglion ridge, and from it the spinal and cranial nerve ganglia and the ganglia of the sympathetic nervous system are developed. By the upward growth of the mesoderm the neural tube is ultimately separated from the overlying ectoderm. The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future fore-brain (prosencephalon), mid-brain (mesencephalon), and hind- brain (rhombencephalon). The walls of the vesicles are developed into the nervous tissue and neuroglia of the brain, and their cavities are modified to form its ventricles.

As a result of cell signaling interactions between the ectoderm and underlying mesoderm cells, formation of the developing limb bud occurs as mesenchymal cells from the lateral plate mesoderm and somites begin to proliferate to the point where they create a bulge under the ectodermal cells above. The mesoderm cells in the limb bud that come from the lateral plate mesoderm will eventually differentiate into the developing limb’s connective tissues, such as cartilage, bone, and tendon. Moreover, the mesoderm cells that come from the somites will eventually differentiate into the myogenic cells of the limb muscles. The limb bud remains active throughout much of limb development as it stimulates the creation and positive feedback retention of two signaling regions: the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) with the mesenchymal cells.

The trigeminal and facial motor nuclei were also shown to not correlate well with the rhombomere boundaries in the lamprey. Several studies have shown that the fibroblast growth factor (FGF) is secreted from the midbrain-rhombomere 1 boundary. These proteins instruct cell behavior in the surrounding neuroectoderm. However, the mechanism behind the integration of the signal and the actions that follow remains unclear. Studies have shown that the FGF receptors, or FGFRs act partially redundantly to support cell survival in the dorsal ectoderm, promote r1 tissue identity, and regulate the production of ventral neuronal populations, including the midbrain dopaminergic neurons. In mice, while mutations of the fgfr2 and fgfr3 did not interfere with the development of the midbrain and r1, mutation of fgfr1 caused midbrain and r1 defects.

In front of the primitive streak, two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line formed by the streak. These are named the neural folds; they commence some little distance behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove. The groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or canal, the ectodermal wall of which forms the rudiment of the nervous system.

Additionally, EBs can be formed from embryonic stem cells derived through alternative techniques, including somatic cell nuclear transfer or the reprogramming of somatic cells to yield induced pluripotent stem cells (iPS). Similar to ESCs cultured in monolayer formats, ESCs within embryoid bodies undergo differentiation and cell specification along the three germ lineages – endoderm, ectoderm, and mesoderm – which comprise all somatic cell types. In contrast to monolayer cultures, however, the spheroid structures that are formed when ESCs aggregate enables the non-adherent culture of EBs in suspension, making EB cultures inherently scalable, which is useful for bioprocessing approaches, whereby large yields of cells can be produced for potential clinical applications. Additionally, although EBs largely exhibit heterogeneous patterns of differentiated cell types, ESCs are capable of responding to similar cues that direct embryonic development.

BMP4 is important for bone and cartilage metabolism. The BMP4 signaling has been found in formation of early mesoderm and germ cells. Limb bud regulation and development of the lungs, liver, teeth and facial mesenchyme cells are other important functions attributed to BMP4 signaling. Digit formation is influenced by BMP4, along with other BMP signals. The interdigital mesenchyme exhibits BMP4, which prevents apoptosis of the region. Tooth formation relies on BMP4 expression, which induces Msx 1 and 2. These transcription factors turn the forming tooth to become and incisor. BMP4 also plays important roles in adipose tissue: it is essential for white adipogenesis, and promotes adipocyte differentiation. Additionally, it is also important for brown fat, where it induces UCP1, related to non-shivering thermogenesis. BMP4 secretion helps cause differentiation of the ureteric bud into the ureter. BMP4 antagonizes organizer tissue and is expressed in early development in ectoderm and mesoderm tissue.

In the development of vertebrate animals, the prechordal plate is a "uniquely thickened portion" of the endoderm that is in contact with ectoderm immediately rostral to the cephalic tip of the notochord.Mondofacto: Online Medical Dictionary It is the most likely origin of the rostral cranial mesoderm.Seifert, R; et al. J Anat 1993 183:75-89 STAGE 6 The prechordal plate is a thickening of the endoderm at the cranial end of the primitive streak seen in Embryo Beneke by Hill J.P., Florian J (1963) STAGE 7 The prechordal plate is described as a median mass of cells, located at the anterior end of the notochord, which appears in early embryos as an integral part of the roof of the foregut. e.g. Embryos Bi 24 and Manchester 1285. O'Rahilly R., Müller F. (1987) p 55 and Gilbert P.W., (1957) STAGE 8 O'Rahilly R., Müller F. (1987) present a detailed discussion of the term 'prechordal plate' and its relation to the 'prochordal plate'.

Jade1 expression was detected in extraembryonic ectoderm and trophoblast, which are placental components important for vasculogenesis, as well as in sites enriched with multipotent or tissue-specific progenitors, including neural progenitors(2). The dynamics of Jade1 reporter expression in these areas indicates the involvement in the determination and elongation of anterior posterior axis, an important point of the study). The potential role for human JADE1 in the renewal of embryonic stem cell and embryonal carcinoma cell cultures was suggested in another screening study which showed that, in cultured stem cells activation of stem cell transcription factor OCT4 pathway upregulated JADE1 gene expression along with stem cell factors NANOG, PHC1, USP44 and SOX2. Role of JADE1 in epithelial cell proliferation was addressed in a murine model of acute kidney injury and regeneration. Expression patterns and dynamics of HBO1-JADE1S/L were examined in regenerating tubular epithelial cells. Ischemia and reperfusion injury resulted in an initial decrease in JADE1S, JADE1L, and HBO1 protein levels, which returned to the baseline during renal recovery.