Ryden has peopled Ratmansky's stage with furry animals that look like fairground prizes, a gum-ball lady resembling a blastula, and various creatures that slither on the floor and wag their ears.
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On the first screen I thought I saw a chick or a frog taking shape, though the creature would palpitate into an egg, a lumpen lime or a blastula of germinating cells.
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But before you can say blastula, his wife — he begins by calling her Clo, then just goes with her real name, Jen — is crying all the time and sending all-caps texts about pretzels.
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In vitro fertilisation involves implantation of a blastula into a mother's uterus. Blastula cell implantation could serve to eliminate infertility.
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The blastula precedes the formation of the gastrula in which the germ layers of the embryo form. A common feature of a vertebrate blastula is that it consists of a layer of blastomeres, known as the blastoderm, which surrounds the blastocoel.Forgács & Newman, 2005: p. 27 In mammals, the blastula is referred to as a blastocyst.
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Sea stars are deuterostomes and the first cleavage begins shortly after fertilization and is holoblastic. Fourteen hours after fertilization, a wrinkled blastula is formed. Twenty hours after fertilization, a blastula with an invaginated pore at the vegetal pole forms. The blastula then rotates around an axis in circular motions, the embryos then undergo a longitudinal stretching.
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After the 7th cleavage has produced 128 cells, the morula becomes a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel or blastocyst). Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula. The blastocyst must not be confused with the blastula; even though they are similar in structure, their cells have different fates.
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In developmental biology, midblastula or midblastula transition (MBT) occurs during the blastula stage of embryonic development. During this stage, the embryo is referred to as a blastula. The series of changes to the blastula that characterize the midblastula transition include activation of zygotic gene transcription, slowing of the cell cycle, increased asynchrony in cell division, and an increase in cell motility.
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Blastocoel and blastoderm Blastulation is the stage in early animal embryonic development that produces the blastula. The blastula (from Greek βλαστός ( meaning sprout) is a hollow sphere of cells (blastomeres) surrounding an inner fluid-filled cavity (the blastocoel). Embryonic development begins with a sperm fertilizing an egg cell to become a zygote, which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoel is formed does the early embryo become a blastula.
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Important to the sea urchin blastula is the ingression of the primary mesenchyme. After the blastula hatches from the fertilization envelope, the vegetal side of the blastula begins to flatten and thicken as a small cluster of these cells develop long, thin processes called filopodia. These cells then dissociate and ingress into the blastocoel and are called the primary mesenchyme. The cells move randomly along the inside of the blastocoel, until they become localized in the ventrolateral region of the blastocoel.
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The BCNE center is the Blastula Chordin and Noggin Expressing center. The BCNE center is located in the dorsal region of the animal pole. It appears after the mid-blastula stage and is triggered by the expression of beta-catenin like the Nieuwkoop center. This center is found to be distinct from the Nieuwkoop center, which secretes a different group of factors, due to expression of VegT and B1-Sox which prevents the BCNE center from extending into the vegetal pole of the blastula.
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Mesoderm induction: from caps to chips. Nature Rev Genet 7:360-72. 3\. Heasman J. 1997. Patterning the Xenopus blastula.
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Reduction of expression of β-catenin in the nucleus correlated with loss of vegetal cell fates. Transplants of micromeres lacking nuclear accumulation of β-catenin were unable to induce a second axis. For the molecular mechanism of β-catenin and the micromeres, it was observed that Notch was present uniformly on the apical surface of the early blastula but was lost in the secondary mesenchyme cells (SMCs) during late blastula and enriched in the presumptive endodermal cells in late blastula. Notch is both necessary and sufficient for determination of the SMCs.
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The blastodisc is a round single-cell layer of cells inside the blastula from which the embryo is going to form.
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A blastula is a sphere of cells surrounding a blastocoel. The blastocoel is a fluid filled cavity which contains amino acids, proteins, growth factors, sugars, ions and other components which are necessary for cellular differentiation. The blastocoel also allows blastomeres to move during the process of gastrulation. In Xenopus embryos, the blastula is composed of three different regions.
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The study of the blastula and of cell specification has many implications in stem cell research and assisted reproductive technology. In Xenopus, blastomeres behave as pluripotent stem cells which can migrate down several pathways, depending on cell signaling. By manipulating the cell signals during the blastula stage of development, various tissues can be formed. This potential can be instrumental in regenerative medicine for disease and injury cases.
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The formation of the blastocoel is a critical stage in the formation of the blastocyst, which is a blastula where some cellular differentiation has already occurred.
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Pluteus larva has bilateral symmetry. In most cases, the female's eggs float freely in the sea, but some species hold onto them with their spines, affording them a greater degree of protection. The unfertilized egg meets with the free-floating sperm released by males, and develops into a free-swimming blastula embryo in as few as 12 hours. Initially a simple ball of cells, the blastula soon transforms into a cone-shaped echinopluteus larva.
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Although vertical transmission of the symbionts is pivotal, the underlying and cellular mechanisms of this process are relatively unknown. However, there are several existing hypotheses. One theory is that the microorganisms circulating in the hemolymph of the mother migrate to a posterior region of the offspring blastula containing enlarged follicle cells. Other studies suggest that symbionts are directly transferred from the maternal bacteriocyte to the follicular region of the blastula through exocytic and endocytic transport.
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Tight junctions are very important in embryo development. In the blastula, these cadherin mediated cell interactions are essential to development of epithelium which are most important to paracellular transport, maintenance of cell polarity and the creation of a permeability seal to regulate blastocoel formation. These tight junctions arise after the polarity of epithelial cells is established which sets the foundation for further development and specification. Within the blastula, inner blastomeres are generally non-polar while epithelial cells demonstrate polarity.
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Blastula-stage cells can behave as pluripotent stem cells in many species. Pluripotent stem cells are the starting point to produce organ specific cells that can potentially aid in repair and prevention of injury and degeneration. Combining the expression of transcription factors and locational positioning of the blastula cells can lead to the development of induced functional organs and tissues. Pluripotent Xenopus cells, when used in an in vivo strategy, were able to form into functional retinas.
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The LaBonne lab also demonstrated a role for FGF signaling in the retention of pluripotency underling neural crest genesis, and discovered that a novel switching of effector pathways, from Map Kinase to PI3 Kinase, controls the transit from pluripotency to lineage restriction. Recent work in the LaBonne lab has focused on the epigenetic control of pluripotency in naïve blastula cells, including a central role for HDAC activity in both maintaining blastula pluripotentcy and establishment of the neural crest stem cell population.
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In biology, a blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation.Blastomere Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc.
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Early development differences between deuterostomes versus protostomes. In deuterostomes, blastula divisions occur as radial cleavage because they occur parallel or perpendicular to the major polar axis. In protostomes the cleavage is spiral because division planes are oriented obliquely to the polar major axis. During gastrulation, deuterostome embryos' anus is given first by the blastopore while the mouth is formed secondarily, and vice versa for the protostomes In both deuterostomes and protostomes, a zygote first develops into a hollow ball of cells, called a blastula.
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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.
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In bilateral animals cleavage can be either holoblastic or meroblastic depending on the species. During gastrulation the blastula develops in one of two ways that divide the whole animal kingdom into two-halves (see: Embryological origins of the mouth and anus). If in the blastula the first pore, or blastopore, becomes the mouth of the animal, it is a protostome; if the blastopore becomes the anus then it is a deuterostome. The protostomes include most invertebrate animals, such as insects, worms and molluscs, while the deuterostomes include the vertebrates.
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At the 120- cell stage, the sea urchin embryo is considered a blastula because of its developed blastocoel, which every embryonic cell surrounds and touches. Every cell is in contact with the proteinaceous fluid of the blastocoel on the inside and touches the hyaline layer on the outside. The loosely connected blastomeres are now tightly connected because of tight junctions that create a seamless epithelium that completely encircles the blastocoel. Even as the blastomeres continue to divide, the blastula remains one-cell thick and thins out as the embryo expands outward.
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In amniotes (reptiles, birds and mammals), gastrulation involves the creation of the blastopore, an opening into the archenteron. Note that the blastopore is not an opening into the blastocoel, the space within the blastula, but represents a new inpocketing that pushes the existing surfaces of the blastula together. In amniotes, gastrulation occurs in the following sequence: (1) the embryo becomes asymmetric; (2) the primitive streak forms; (3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.
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The blastula stage of early embryo development begins with the appearance of the blastocoel. The origin of the blastocoel in Xenopus has been shown to be from the first cleavage furrow, which is widened and sealed with tight junctions to create a cavity. In many organisms the development of the embryo up to this point and for the early part of the blastula stage is controlled by maternal mRNA, so called because it was produced in the egg prior to fertilization and is therefore exclusively from the mother.
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In due course, the blastula changes into a more differentiated structure called the gastrula. Soon after the gastrula is formed, three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop.
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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).
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A cDNA library from the blastula stage of a frog embryo was cloned into RNA expression plasmids to generate synthetic mRNA. The mRNA was then injected into several Xenopus embryos at a four-cell stage and looked in early blastula embryos for an expansion of the region of the ectodermal marker Sox2 and diminution of the expression of the mesodermal marker Xbra. Ectodermin was one out of 50 clones to present this phenotype when injected into embryos. The identification of FAM was done through a siRNA screen to find deubiquitinases that regulate the response to TGFβ.
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During cleavage, the overall size of the embryo does not change, but the size of individual cells decrease rapidly as they divide to increase the total number of cells. Cleavage results in a blastula. Depending on the species, a blastula stage embryo can appear as a ball of cells on top of yolk, or as a hollow sphere of cells surrounding a middle cavity. The embryo's cells continue to divide and increase in number, while molecules within the cells such as RNAs and proteins actively promote key developmental processes such as gene expression, cell fate specification, and polarity.
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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.
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It is difficult to relate shell size at the onset of maturity to age since the size structure of populations vary over time and from one locality to another. Dissection of Tarebia granifera showed blastula stage embryos in the brood pouches of snails as small as 8 mm shell height. Small numbers of shelled embryos, including veligers, were found in snails of 10–14 mm but became more plentiful in snails >14 mm and especially those >20 mm. Importantly, unshelled embryos (blastula, gastrula and trochophore stages) were not found in snails >16 mm and the numbers of shelled embryos themselves decreased in the largest snails, >24 mm.
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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.
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The pharyngula is a stage in the embryonic development of vertebrates. At this stage, the embryos of all vertebrates are similar, having developed features typical of vertebrates, such as the beginning of a spinal cord. Named by William Ballard, the pharyngula stage follows the blastula, gastrula and neurula stages.
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The oviduct cells stimulate these trophoblast sodium pumps as the fertilized egg travels down the fallopian tube towards the uterus. As the embryo further divides, the blastocoel expands and the inner cell mass is positioned on one side of the trophoblast cells forming a mammalian blastula, called a blastocyst.
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This work proposed that Myc plays this key role in many stem cell populations, and more recent work by others has shown this to be the case. LaBonne’s group subsequently demonstrated that Id3 was a key Myc target in maintaining neural crest potency. The growing realization of the commonalities between pluripotent blastula inner cell mass cells/embryonic stem cells and neural crest cells led LaBonne’s group to proposed a new model in which neural crest cells arose via retention of the regulatory network controlling pluripotency in blastula cells and showed that neural crest cells possess a previously unrecognized capacity to form endoderm. This pioneering work created a new framework for studying these developmentally and clinically important cells.
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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.
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Yolk plug is the remaining patch of endodermal cells that is created during the formation of the dorsal lip of the blastopore in the amphibian. It is a patch of large endodermal cells which remains exposed on the vegetal surface of the blastula that will eventually be internalized by epiboly.
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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.
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Cilia first appear during the middle blastula stage, followed by eight membranes inside the body. About twenty-five days after the eggs have been shed, fixation will occur. The base will form the shape of a disc and grow, the mouth opens, the larva shorten, and finally the anemones become largely dormant.
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Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. During this time three cell populations become distinguished. The first population is the yolk syncytial layer.
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In the first stages of embryonic development, a single-celled zygote undergoes many rapid cell divisions, called cleavage, to form a blastula, which looks similar to a ball of cells. Next, the cells in a blastula-stage embryo start rearranging themselves into layers in a process called gastrulation. These layers will each give rise to different parts of the developing multicellular organism, such as the nervous system, connective tissue, and organs. A newly developing human is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a fetus. In other multicellular organisms, the word “embryo” can be used more broadly to any early developmental or life cycle stage prior to birth or hatching.
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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.
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312(1): 90-102. Signals from the Nieuwkoop center induce the Spemann-Mangold organizer, thus the Nieuwkoop Center is known as the organizer of the organizer. Even with the BCNE center removed from the blastula, the Nieuwkoop Center is able to induce formation of the Spemann-Mangold organizer. E.M. De Robertis and H. Kuroda (2004).
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The BCNE center is found to secrete several factors: chordin, noggin, Xnr3, siamois, goosecoid, twin, Admp, and FoxA4a. This center predisposes cells in the blastula stage to become neural tissue. The cells of the BCNE region give rise to the forebrain, most of the mid-brain and hind-brain, the notochord, and the floor plate.
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London: MacMillan & Co. It includes a blastula, gastrula and a four armed echinopluteus stage that forms an important part of the zooplankton.MacBride, E.W., 1903. The development of Echinus esculentus together with some points on the development of E. miliaris and E. acutus. Philosophical Transactions of the Royal Society of London, Series B, 195, 285-327.
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Retrieved on 25 July 2012. and is named after the structure that forms in the blastula during these early stages. Initially funded by the Wellcome Trust,The art of science Times Higher Education, London, 10 October 1997. Retrieved on 25 July 2012 Primitive Streak was first exhibited at London’s Institute of Contemporary Arts in 1997Kohn, Marek.
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By the late blastula stage, the Xenopus embryos have a clear dorsal/ventral axis. In the early gastrula, most of the tissue in the embryo is not determined. The one exception is the anterior portion of the dorsal blastopore lip. When this tissue was transplanted to another part of the embryo, it developed as it normally would.
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In addition, this tissue was able to induce the formation of another dorsal/ventral axis. Hans Spemann named this region the organizer and the induction of the dorsal axis the primary induction. The organizer is induced from a dorsal vegetal region called the Nieuwkoop center. There are many different developmental potentials throughout the blastula stage embryos.
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A newer hypothesis suggests that a membranous conduit forms between the maternal bacteriocyte and blastula which acts as a bridge for symbionts. Additionally, some studies show that the recognition of stem cell niches and association with dynein, kinesin, and microtubules are crucial for transmission from the parent to the offspring germline as well as segregation to host daughter cells.
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300x300px In developmental biology, invagination is a mechanism that takes place during gastrulation. This mechanism or cell movement happens mostly in the vegetal pole. Invagination consists of the folding of an area of the exterior sheet of cells towards the inside of the blastula. In each organism, the complexity will be different depending on the number of cells.
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Invagination process in Amphioxus The invagination in Amphioxus is the first cell movement of gastrulation. This process was first described by Conklin. During gastrulation, the blastula will be transformed by the invagination. The endoderm will fold towards the inner part and that way the blastocoel will be gone transforming into like a cup- shaped structure with a double wall.
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The trophoblast gives rise to the placenta. The name "blastocyst" arises from the Greek ' ("a sprout") and ' ("bladder, capsule"). In other animals this is called a blastula. In humans, blastocyst formation begins about 5 days after fertilization when a fluid-filled cavity opens up in the morula, the early embryonic stage of a ball of 16 cells.
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Fertilization leads to the formation of a zygote. During the next stage, cleavage, mitotic cell divisions transform the zygote into a hollow ball of cells, a blastula. This early embryonic form undergoes gastrulation, forming a gastrula with either two or three layers (the germ layers). In all vertebrates, these progenitor cells differentiate into all adult tissues and organs.
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After fertilization, S. officinalis embryos develop in choanosomal tissue of the female sponge. Cleavage of cells begins after fertilization, around November, and is total and equal. By May, a stereoblastula, or a blastula without a clear central cavity, forms. From May to July, parenchymella larva, or larva which is a mass of cells enveloped in flagellated cells, develop.
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The mid-blastula transition is also characterized by a marked increase in transcription of new, non-maternal mRNA transcribed from the genome of the organism. Large amounts of the maternal mRNA are destroyed at this point, either by proteins such as SMAUG in Drosophila or by microRNA. These two processes shift the control of the embryo from the maternal mRNA to the nuclei.
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The discovery of the organizer influenced many embryonic induction projects in Japan. For example, T. Yamada created the double potential theory for the induction process in embryos. Another discovery after the organizer discovery was the modified Vogt fate map using newt and Xenopus blastula by researcher Osamu Nakamura. The new concept of transdifferentiation was proposed by T.S. Okada and G. Eguchi.
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E-cadherin is first expressed in the 2-cell stage of mammalian development, and becomes phosphorylated by the 8-cell stage, where it causes compaction. In adult tissues, E-cadherin is expressed in epithelial tissues, where it is constantly regenerated with a 5-hour half-life on the cell surface. Cell–cell interactions mediated by E-cadherin are crucial to blastula formation in many animals.
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The trophoblast cells become extraembryonic structures necessary for development. After the initial formation of the morula, it does not have an interior space or cavity. Cavitation occurs to create a cavity on the inside of the morula. This process occurs when trophoblast cells, in other words the outside covering of the blastocyst, secretes fluid into the morula creating the blastocoel, the fluid filled cavity of the blastula.
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In sea urchins the first cells to internalize are the primary mesenchyme cells (PMCs), which have a skeletogenic fate, which ingress during the blastula stage. Gastrulation – internalization of the prospective endoderm and non- skeletogenic mesoderm – begins shortly thereafter with invagination and other cell rearrangements the vegetal pole, which contribute approximately 30% to the final archenteron length. The gut's final length depends on cell rearrangements within the archenteron.
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Due to the fact that placental mammals and marsupials nourish their developing embryos via the placenta, the ovum in these species does not contain significant amounts of yolk, and the yolk sac in the embryo is relatively small in size, in comparison with both the size of the embryo itself and the size of yolk sac in embryos of comparable developmental age from lower chordates. The fact that an embryo in both placental mammals and marsupials undergoes the process of implantation, and forms the chorion with its chorionic villi, and later the placenta and umbilical cord, is also a difference from lower chordates. The difference between a mammalian embryo and an embryo of a lower chordate animal is evident starting from blastula stage. Due to that fact, the developing mammalian embryo at this stage is called a blastocyst, not a blastula, which is more generic term.
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In tunicates, invagination is the first mechanism that takes place during gastrulation. The four largest endoderm cells induce the invagination process in the tunicates. Invagination consists of the internal movements of a sheet of cells (the endoderm) based on changes in their shape. The blastula of the tunicates is a little flattened in the vegetal pole making a change of shape from a columnar to a wedge shape.
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As the eggs mature they will begin to go through segmentation (becoming covered with rounded masses or segments). The egg will grow and a membrane will form before taking on a more spherical shape. Next, they will go through gastrulation, where they develop multiple layers. The wall of the blastula will flatten and sink downwards, and the egg will often flatten itself again, becoming the gastrula made up of three layers.
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The zygote develops by mitosis, and when it has developed into 16 cells becomes known as the morula. Until this stage in development, all cells (blastomeres) are autonomous and not specified to any fate. In many animals, the morula then develops by cavitation to become the blastula. Cellular differentiation then develops the blastula's cells into two types: trophoblast cells that surround the blastocoel and an inner mass of cells (the embryoblast).
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This is accomplished in part due to the influx of water that expands the blastocoel and pushes the cells surrounding it outwards. At this point, the cells have become specified and are ciliated on the opposite side of the blastocoel. The vegetal plate and animal hemisphere develop and secrete a hatching enzyme that digests the fertilization envelope and allows the embryo to now become a free-swimming hatched blastula.
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The animal cap forms the roof of the blastocoel and goes on primarily to form ectodermal derivatives. The equatorial or marginal zone, which compose the walls of the blastocoel differentiate primarily into mesodermal tissue. The vegetal mass is composed of the blastocoel floor and primarily develops into endodermal tissue. In the mammalian blastocyst (term for mammalian blastula) there are three lineages that give rise to later tissue development.
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Urticina crassicornis's major sperm chromosomal proteins have been found to be two specialized histone H1 proteins which indicate a strong relation to the chromosomal proteins of bird and amphibians.Ausio, Juan, Rocchini, Corinne, Zhang, Fan. Two Specialized Histone H1 proteins are the major sperm of the sea anemone Urticina (Tealia) crassicornis. Victoria, BC: Department of Biochemistry and Microbiology, University of Victoria, 1995 After fertilization, a solid and ciliated blastula is created due to superficial cleavage.
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This undergoes a period of divisions to form a ball or sheet of similar cells called a blastula or blastoderm. These cell divisions are usually rapid with no growth so the daughter cells are half the size of the mother cell and the whole embryo stays about the same size. They are called cleavage divisions. Mouse epiblast primordial germ cells (see Figure: “The initial stages of human embryogenesis”) undergo extensive epigenetic reprogramming.
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A walrus pup at Kamogawa Seaworld, Japan Gestation lasts 15 to 16 months. The first three to four months are spent with the blastula in suspended development before it implants itself in the uterus. This strategy of delayed implantation, common among pinnipeds, presumably evolved to optimize both the mating season and the birthing season, determined by ecological conditions that promote newborn survival. Calves are born during the spring migration, from April to June.
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The morula is the precursor structure to the blastula, which is an animal embryo in the early stages of development. The morula consists of a cluster of internal cells covered by a layer of external cells. The internal cells become the inner cellular mass, which becomes the entire embryo. The external cells are destined to become a structure called the trophoblast, a layer of tissue on the inside of the embryo that provides it with nourishment.
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Usually even before its liberation, the ovum initiates cleavage processes in which it becomes completely pinched through at the middle. A ball of cells characteristic of animals, the blastula, is ultimately produced in this manner, with a maximum of 256 cells. Development beyond this 256-cell stage has not yet been observed. Trichoplax lack a homologue of the Boule protein that appears to be ubiquitous and conserved in males of all species of other animals tested.
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In the life cycle of Elysia chlorotica, cleavage is holoblastic and spiral. This means that the eggs cleave completely (holoblastic); and each cleavage plane is at an oblique angle to the animal-vegetal axis of the egg. The result of this is that tiers of cells are produced, each tier lying in the furrows between cells of the tier below it. At the end of cleavage, the embryo forms a stereoblastula, meaning a blastula without a clear central cavity.
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An unhealthy or malnourished cell will get stuck at this checkpoint. The G2/M checkpoint is where the cell ensures that it has enough cytoplasm and phospholipids for two daughter cells. But sometimes more importantly, it checks to see if it is the right time to replicate. There are some situations where many cells need to all replicate simultaneously (for example, a growing embryo should have a symmetric cell distribution until it reaches the mid- blastula transition).
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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.
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The animal cells are not determined because the micromeres can induce the animal cells to also take on mesodermal and endodermal fates. It was observed that β-catenin was present in the nuclei at the vegetal pole of the blastula. Through a series of experiments, one study confirmed the role of β-catenin in the cell-autonomous specification of vegetal cell fates and the micromeres inducing ability. Treatments of LiCl sufficient to vegetalize the embryo resulted in increases in nuclearly localized b-catenin.
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Cleavage ends with the formation of the blastula. Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic (total or entire cleavage) or meroblastic (partial cleavage). The pole of the egg with the highest concentration of yolk is referred to as the vegetal pole while the opposite is referred to as the animal pole. Cleavage differs from other forms of cell division in that it increases the number of cells and nuclear mass without increasing the cytoplasmic mass.
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An amphibian embryo in the 128- cell stage is considered a blastula as the blastocoel in the embryo becomes apparent during this stage. The fluid-filled cavity forms in the animal hemisphere of the frog. However, the early formation of the blastocoel has been traced back to the very first cleavage furrow. It was demonstrated in the frog embryo that the first cleavage furrow widens in the animal hemisphere creating a small intercellular cavity that is sealed off via tight junctions.
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Embryonic development of salamander, circa the 1920s Embryos (and one tadpole) of the wrinkled frog (Rana rugosa) In animals, fertilization begins the process of embryonic development with the creation of a zygote, a single cell resulting from the fusion of gametes (e.g. egg and sperm). The development of a zygote into a multicellular embryo proceeds through a series of recognizable stages, often divided into cleavage, blastula, gastrulation, and organogenesis. Cleavage is the period of rapid mitotic cell divisions that occur after fertilization.
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Another common argument against dualism consists in the idea that since human beings (both phylogenetically and ontogenetically) begin their existence as entirely physical or material entities and since nothing outside of the domain of the physical is added later on in the course of development, then we must necessarily end up being fully developed material beings. There is nothing non-material or mentalistic involved in conception, the formation of the blastula, the gastrula, and so on. The postulation of a non-physical mind would seem superfluous.
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In deuterostomes, the early divisions occur parallel or perpendicular to the polar axis. This is called radial cleavage, and also occurs in certain protostomes, such as the lophophorates. Most deuterostomes display indeterminate cleavage, in which the developmental fate of the cells in the developing embryo is not determined by the identity of the parent cell. Thus, if the first four cells are separated, each can develop into a complete small larva; and if a cell is removed from the blastula, the other cells will compensate.
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However, cells from the Nieuwkoop Center express potent mesoderm inducers as well as the secreted protein, Cerebrus (CER1), which contributes to the formation of the head, heart, and asymmetry of internal organs. Furthermore, a homeobox gene, nieuwkoid, was named after the Nieuwkoop Center for its role in development. Nieuwkoid is expressed immediately following the mid-blastula transition to a pregastrula embryo on the dorsal side and mis-expression of nieuwkoid was found to be sufficient for induction of secondary axes. D.S. Koos and R.K. Ho (1998).
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Stylized cutaway diagram of an animal cell (with flagella) The kingdom Animalia contains multicellular organisms that are heterotrophic and motile (although some have secondarily adopted a sessile lifestyle). Most animals have bodies differentiated into separate tissues and these animals are also known as eumetazoans. They have an internal digestive chamber, with one or two openings; the gametes are produced in multicellular sex organs, and the zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells.
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DNA methylation patterns are largely erased and then re-established between generations in mammals. Almost all of the methylations from the parents are erased, first during gametogenesis, and again in early embryogenesis, with demethylation and remethylation occurring each time. Demethylation in early embryogenesis occurs in the preimplantation period in two stages – initially in the zygote, then during the first few embryonic replication cycles of morula and blastula. A wave of methylation then takes place during the implantation stage of the embryo, with CpG islands protected from methylation.
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Poem Rocket's national (and/or international) touring history is uncertain, though they were known to play frequently around the New York City area in the 1990s at avant-garde music clubs such as The Knitting Factory and The Cooler, and probably CBGB's. They are known to have played live with Blastula, Wharton Tiers Ensemble, Mecca Normal, labelmates Slug (rock band, not rap group), Tono-Bungay, Bride Of No-No, Pilot To Gunner, Sweep the Leg Johnny, and Hippopotamus. They are believed to have played live with their recording partners Six Finger Satellite.
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The parts that are autotomised or the buds may develop directly into fully formed larvae or may develop through a gastrula or even a blastula stage. The parts that develop into the new larvae vary from the preoral hood (a mound like structure above the mouth), the side body wall, the postero-lateral arms or their rear ends. The process of cloning is a cost borne by the larva both in resources as well as in development time. Larvae have been observed to undergo this process when food is plentiful or temperature conditions are optimal.
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During the blastula and gastrula stages, vegetal cells (the presumptive endoderm), release signals to marginal zone cells resulting in the induction and patterning of the mesoderm (1, 8). One of these signals, FGF, achieves this through the regulation of T box transcription factors, a strategy which is shared among Xenopus, mouse and zebrafish (9). Upon FGF binding to its receptor, FGFR, the receptor pair dimerizes and is transphosphorylated, enabling it to recruit proteins that activate Ras and Raf. This is followed by the subsequent phosphorylation of MEK and MAPK.
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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.
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The zygote contains a full complement of genetic material, with all the biological characteristics of a single human being, and develops into the embryo. Briefly, embryonic development have four stages: the morula stage, the blastula stage, the gastrula stage, and the neurula stage. Prior to implantation, the embryo remains in a protein shell, the zona pellucida, and undergoes a series of rapid mitotic cell divisions called cleavage. A week after fertilization the embryo still has not grown in size, but hatches from the zona pellucida and adheres to the lining of the mother's uterus.
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As for many animals, the egg cell of any extant ambulacrarian by cell division evolves to a blastula ("cell ball"), which evolves to a triploblast ("three- layered") gastrula. The gastrula then evolves to a dipleurula larva form, which is specific for the ambulacraria. This, in its turn, is developed in various different kinds of larvae for different taxa of ambulacrarians. It has been suggested that the adult form of the last common ancestor of the ambulacrarians was anatomically similar to the dipleurula larvae, whence this hypothetic ancestor sometimes also is called dipleurula.
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The primitive streak is a structure that forms in the blastula during the early stages of avian, reptilian and mammalian embryonic development. It forms on the dorsal (back) face of the developing embryo, toward the caudal or posterior end. The presence of the primitive streak will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation. To form the streak, reptiles, birds and mammals arrange mesenchymal cells along the prospective midline, establishing the second embryonic axis, as well as the place where cells will ingress and migrate during the process of gastrulation and germ layer formation.
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A type of incompatibility that is found as often in plants as in animals occurs when the egg or ovule is fertilized but the zygote does not develop, or it develops and the resulting individual has a reduced viability. This is the case for crosses between species of the frog genus, where widely differing results are observed depending upon the species involved. In some crosses there is no segmentation of the zygote (or it may be that the hybrid is extremely non-viable and changes occur from the first mitosis). In others, normal segmentation occurs in the blastula but gastrulation fails.
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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.
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Early development differences between protostomes versus deuterostomes. In protostomes blastula divisions occur as spiral cleavage because division planes are oriented obliquely to the polar major axis. In deuterostomes, the cleavage is radial because planes are parallel or perpendicular to the major polar axis. During gastrulation, protostome embryos' mouth is given first by the blastopore while the anus is formed later, and vice versa for the deuterostomes In animals at least as complex as earthworms, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the growth of the gut.
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Multiple studies have established that Nodal signal is required for the induction of most mesodermal and endodermal cell types and Squint/Cyclops knockouts in Zebrafish do not develop notochord, heart, kidneys or even blood. The origin and expression pattern of the nodal signaling proteins differs in different species. Mammalian nodal signaling is initiated ubiquitously in epiblast cells and is maintained by autoregulatory signaling of Wnt3 and limited by the induction of antagonists such as Cerberus-like and lefty. Studies in Xenopus have found that xnr expression (the Xenopus nodal) is induced by VegT at the vegetal pole and nodals spread to the blastula.
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The composition of the milk produced by the mother varies according to the needs of the joey. In addition, red kangaroo mothers may "have up to three generations of offspring simultaneously; a young-at-foot suckling from an elongated teat, a young in the pouch attached to a second teat and a blastula in arrested development in the uterus".McCullough, Dale R. and McCullough, Yvette (2000) Kangaroos in Outback Australia, Columbia University Press. . The red kangaroo has also been observed to engage in alloparental care, a behaviour in which a female may adopt another female's joey.
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Sea urchin blastula During early development, the sea urchin embryo undergoes 10 cycles of cell division, resulting in a single epithelial layer enveloping the blastocoel. The embryo then begins gastrulation, a multipart process which dramatically rearranges its structure by invagination to produce the three germ layers, involving an epithelial-mesenchymal transition; primary mesenchyme cells move into the blastocoel and become mesoderm.; ; ; ; ; ; ; ; ; It has been suggested that epithelial polarity together with planar cell polarity might be sufficient to drive gastrulation in Sea urchin. The development of a regular sea urchin An unusual feature of sea urchin development is the replacement of the larva's bilateral symmetry by the adult's broadly fivefold symmetry.
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In most species, this larva has 12 elongated arms lined with bands of cilia that capture food particles and transport them to the mouth. In a few species, the blastula contains supplies of nutrient yolk and lacks arms, since it has no need to feed. Several months are needed for the larva to complete its development, the change into the adult form beginning with the formation of test plates in a juvenile rudiment which develops on the left side of the larva, its axis being perpendicular to that of the larva. Soon, the larva sinks to the bottom and metamorphoses into a juvenile urchin in as little as one hour.
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The fertilized eggs develop into larvae by dividing until there are enough cells to form a hollow sphere (blastula) and then a depression forms at one end (gastrulation) and eventually becomes the digestive cavity. However, in cnidarians the depression forms at the end further from the yolk (at the animal pole), while in bilaterians it forms at the other end (vegetal pole). The larvae, called planulae, swim or crawl by means of cilia. They are cigar-shaped but slightly broader at the "front" end, which is the aboral, vegetal-pole end and eventually attaches to a substrate if the species has a polyp stage.
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Early echinoderms Along with the chordates and hemichordates, echinoderms are deuterostomes, one of the two major divisions of the bilaterians, the other being the protostomes. During the early development of the embryo, in deuterostomes, the blastopore (the first opening to form) becomes the anus whereas in the protostomes, it becomes the mouth. In deuterostomes, the mouth develops at a later stage, at the opposite end of the blastula from the blastopore, and a gut forms connecting the two. The larvae of echinoderms have bilateral symmetry but this is lost during metamorphosis when their bodies are reorganised and develop the characteristic radial symmetry of the echinoderm, typically pentamerism.
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Ectodermin mRNA is maternally deposited in the animal pole of the egg. In the early blastula stage of the embryo, Ectodermin mRNA and protein forms a gradient that goes from the animal pole (highest concentration) down to the marginal zone (lowest concentration) to prevent TGFβ and nodal signals that induce mesoderm originating from the vegetal pole. Ectodermin mRNA is enriched in the dorsal side of the embryo, and at the end of this stage the expression gradually disappears. Smad4 is ubiquitinated by Ectodermin in the nucleus and exported to the cytoplasm where it can be deubiquitinated by FAM; this way Smad4 can be recycled and be functional again.
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Regarding the paraxial mesoderm from which somites form, fate mapping experiments at the blastula stage show pre-somitic mesoderm progenitors at the site of gastrulation, referred to as the primitive streak in some organisms, in regions flanking the organizer. Transplant experiments show that only at the late gastrula stage are these cells committed to the paraxial fate, meaning that fate determination is tightly controlled by local signals and is not predetermined. For instance, exposure of pre-somitic mesoderm to Bone morphogenetic proteins (BMPs) ventralizes the tissue, however in vivo, BMP antagonists secreted by the organizer (such as Noggin and chordin) prevent this and thus promote the formation of dorsal structures.
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In some species, these develop directly into adults, but in others, there is a free-swimming intermediate stage referred to as a tornaria larva. These are very similar in appearance to the bipinnaria larvae of starfishes, with convoluted bands of cilia running around the body. Since the embryonic development of the blastula within the egg is also very similar to that of echinoderms, this suggests a close phylogenetic link between the two groups. After a number of days or weeks, a groove begins to form around the larval midsection, with the anterior portion eventually destined to become the proboscis, while the remainder forms the collar and trunk.
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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.
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Wnt signaling and beta-catenin dependent gene expression plays a critical role during the formation of different body regions in the early embryo. Experimentally modified embryos that do not express this protein will fail to develop mesoderm and initiate gastrulation. During the blastula and gastrula stages, Wnt as well as BMP and FGF pathways will induce the antero-posterior axis formation, regulate the precise placement of the primitive streak (gastrulation and mesoderm formation) as well as the process of neurulation (central nervous system development). In Xenopus oocytes, β-catenin is initially equally localized to all regions of the egg, but it is targeted for ubiquitination and degradation by the β-catenin destruction complex.
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A blastocoel (), also spelled blastocoele and blastocele, and also called blastocyst cavity (or cleavage or segmentation cavity) is a fluid-filled cavity that forms in the blastula (blastocyst) of early amphibian and echinoderm embryos, or between the epiblast and hypoblast of avian, reptilian, and mammalian blastoderm-stage embryos. It results from cleavage of the oocyte (ovum) after fertilization. It forms during embryogenesis, as what has been termed a "Third Stage" after the single-celled fertilized oocyte (zygote, ovum) has divided into 16-32 cells, via the process of mitosis. It can be described as the first cell cavity formed as the embryo enlarges, the essential precursor for the differentiated, topologically distinct, gastrula.
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The main stalky body of the colony is composed of a coenosarc, which is covered by a protective perisarc. The next generation of the life cycle begins when the medusae are released from the gonozooids, producing free swimming only male medusae velum with gonads, a mouth, and tentacles. The physical appearance of the male and female medusae velum, including their gonads, are indistinguishable, and the sex can only be determined by observing the inside of the gonads, which will either contain sperm or eggs. The medusae reproduce sexually, releasing sperm and eggs that fertilize to form a zygote, which later morphs into a blastula, then a ciliated swimming larva called a planula.
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The blastocyst contains an embryoblast (or inner cell mass) that will eventually give rise to the definitive structures of the fetus, and a trophoblast which goes on to form the extra-embryonic tissues. During blastulation, a significant amount of activity occurs within the early embryo to establish cell polarity, cell specification, axis formation, and to regulate gene expression. In many animals, such as Drosophila and Xenopus, the mid blastula transition (MBT) is a crucial step in development during which the maternal mRNA is degraded and control over development is passed to the embryo. Many of the interactions between blastomeres are dependent on cadherin expression, particularly E-cadherin in mammals and EP-cadherin in amphibians.
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The giant panda is a vulnerable species The use of love darts by the land snail Monachoides vicinus is a form of sexual selection Adult silk worm Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million in total. Animals range in size from 8.5 millionths of a metre to long and have complex interactions with each other and their environments, forming intricate food webs.
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The fact that transdetermination (change of the path of differentiation) often occurs for a group of cells rather than single cells shows that it is induced rather than part of maturation. The researchers were able to identify the minimal conditions and factors that would be sufficient for starting the cascade of molecular and cellular processes to instruct pluripotent cells to organize the embryo. They showed that opposing gradients of bone morphogenetic protein (BMP) and Nodal, two transforming growth factor family members that act as morphogens, are sufficient to induce molecular and cellular mechanisms required to organize, in vivo or in vitro, uncommitted cells of the zebrafish blastula animal pole into a well-developed embryo. Some types of mature, specialized adult cells can naturally revert to stem cells.
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Xenobots, named after the African clawed frog (Xenopus laevis), are synthetic organisms that are automatically designed by computers to perform some desired function and built by combining together different biological tissues. Xenobots are less than a wide and composed of just two things: skin cells and heart muscle cells, both of which are derived from stem cells harvested from early (blastula stage) frog embryos. The skin cells provide rigid support and the heart cells act as small motors, contracting and expanding in volume to propel the xenobot forward. The shape of a xenobot's body, and its distribution of skin and heart cells, are automatically designed in simulation to perform a specific task, using a process of trial and error (an evolutionary algorithm).
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In many organisms including Xenopus and Drosophila, the midblastula transition usually occurs after a particular number of cell divisions for a given species, and is defined by the ending of the synchronous cell division cycles of the early blastula development, and the lengthening of the cell cycles by the addition of the G1 and G2 phases. Prior to this transition, cleavage occurs with only the synthesis and mitosis phases of the cell cycle. The addition of the two growth phases into the cell cycle allows for the cells to increase in size, as up to this point the blastomeres undergo reductive divisions in which the overall size of the embryo does not increase, but more cells are created. This transition begins the growth in size of the organism.
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More recently, using Xenopus egg extracts, it was possible to demonstrate the mitosis-specific function of the nuclear lamin B in regulating spindle morphogenesis and to identify new proteins that mediate kinetochore attachment to microtubules. Embryonic development: Xenopus embryos are widely used in developmental biology. A summary of recent advances made by Xenopus research in recent years would include: #Epigenetics of cell fate specification and epigenome reference maps #microRNA in germ layer patterning and eye development #Link between Wnt signaling and telomerase #Development of the vasculature #Gut morphogenesis #Contact inhibition and neural crest cell migration and the generation of neural crest from pluripotent blastula cells DNA replication: Xenopus cell-free extracts also support the synchronous assembly and the activation of origins of DNA replication. They have been instrumental in characterizing the biochemical function of the prereplicative complex, including MCM proteins.
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Elizabeth Stern was not infertile, but had multiple sclerosis and she and her husband William Stern were worried about the potential health implications of pregnancy, including temporary paralysis, and transmitting genes that might put a child who shared them at risk of developing the same illness. The Sterns and Mary Beth Whitehead entered into a "surrogacy contract," according to which Whitehead would be artificially inseminated with Stern's sperm, and relinquish her parental rights in favor of the Sterns, in return for $10,000, and possibly expenses. According to the initial decision, overruled, Whitehead would be considered a traditional surrogate, as opposed to a gestational surrogate, because she was the genetic mother of the child. The Sterns, both physicians, feared Elizabeth's eggs might carry genes making any child she bore vulnerable to developing MS. While in vitro fertilization of harvested eggs, followed by implantation of a blastula/embryo was an available technology, Elizabeth Stern feared the then-totally-unknown genetic risk factors, the choice repeatedly subject of the Court's questions to Stern and his counsel.
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