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Encyclopedia > Gastrulation
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).
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).

Gastrulation is a phase early in the development of animal embryos, during which the morphology of the embryo is dramatically restructured by cell migration. Gastrulation varies in different phyla. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers. Image File history File links Please see the file description page for further information. ... It has been suggested that this article or section be merged into gastrulation. ... Download high resolution version (801x486, 94 KB) Author Pidalka44. ... Download high resolution version (801x486, 94 KB) Author Pidalka44. ... For the linguistic term, see Phylum (linguistics). ... Organogenesis is a stage of animal development where the ectoderm, endoderm, and mesoderm are formed. ...

Contents

Sea urchins

The following description concerns gastrulation in echinoderms, representative of the triploblasts, or animals with three embryonic germ layers. The illustration, however, depicts the gastrulation of a diploblast, animals with two germ layers. Classes  ?Helicoplacoidea †  ?Arkarua †  ?Homalozoa † Eleutherozoa Asteroidea (1,800 species) Concentricycloidea (2 species) Echinoidea (1,000 species) Holothuroidea (1,000 species) Ophiuroidea (1,500+ species) Pelmatozoa Crinoidea (540+ species) Edrioasteroidea† Blastoidea † Cystoidea † Eocrinoidea † † = extinct Echinoderms (Phylum Echinodermata, from the Greek for spiny skin) are a phylum of marine animals found at... Triploblasty is a condition of the ovum in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. ... Diploblasty is a condition of the ovum in which there are two primary germ layers: the ectoderm and endoderm. ...


Sea urchins deviate from simple cleavage at the fourth cleavage. The four vegetal blastomeres divide unequally to produce four micromeres at the vegetal pole and four macromeres in the middle of the embryo. The animal cells divide meridionally and produce mesomeres. Subclasses Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida (heart urchins) Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida (sand dollars) Order Holectypoida Perischoechinoidea Order Cidaroida (pencil urchins) Sea urchins are small spiny sea creatures... A blastomere is the structure which results from the divisions of a fertilised egg during embryonic development . ... In developmental biology, the term vegetal pole refers to the lower hemisphere of a blastula embryo (as it is conventionally drawn, in reality the vegetal pole may not be the lower hemisphere). ...


At the beginning of vertebrate gastrulation, the embryo is a hollow ball of cells known as the blastula, with an animal pole and a vegetal pole. The vegetal pole begins to flatten to form the vegetal plate. Some of the cells of the vegetal pole detach and through ingression become primary mesenchyme cells. The mesenchyme cells divide rapidly and migrate along the extracellular matrix (basal lamina) to different parts of the blastocoel. The migration is believed to be dependent upon sulfated proteoglycans on the surface of the cells and molecules on the basal lamina such as fibronectin. The cells move by forming filopodia that identify the specific target location. These filopodia then organize into syncytial cables that deposit the calcium carbonate that makes up the spicules (the skeleton of the pluteus larva). Blastulation. ... In developmental biology, the term animal pole refers to the upper hemisphere of a blastula embryo (as it is conventionally drawn, in reality the animal pole may not be the upper hemisphere). ...


During the second phase of gastrulation, the vegetal plate invaginates into the interior, replacing the blastocoelic cavity and thereby forming a new cavity, the archenteron (literally: primitive gut), the opening into which is the blastopore. The arechenteron is elongated by three mechanisms. First, the initial invagination is caused by a differential expansion of the inner layer made of fibropellins and outer layer made of hyalin to cause the layers to bend inward. Second, the archenteron is formed through convergent extension. Convergent extension results when cells intercalate to narrow the tissue and move it forward. Third, secondary mesenchyme pull the tip of the archenteron towards the animal pole. Secondary mesenchyme are formed from cells that ingress from but remain attached to the roof of the archenteron. These cells extend filopodia that use guidance cues to find the future mouth region. Upon reaching the target site, the cells contract to pull the archenteron to fuse with the ectoderm. Once the archenteron reaches the animal pole, a perforation forms, and the archenteron becomes a digestive tract passing all the way through the embryo.


The three embryonic germ layers have now formed. The endoderm, consisting of the archenteron, will develop into the digestive tract. The ectoderm, consisting of the cells on the outside of the gastrula that played little part in gastrulation, will develop into the skin and the central nervous system. The mesoderm, consisting of the mesenchyme cells that have proliferated in the blastocoel, will become all the other internal organs.


Amphibians

During cleavage in amphibians, a higher density of yolk in the vegetal half of the embryo results in the blastocoel cavity being placed asymmetrically in the animal half of the embryo. Unlike in sea urchins, the cells surrounding the blastocoel are thicker than a monolayer. The blastocoel cavity prevents signaling between the animal cap and provides a space for involuting cells during gastrulation.


There are four kinds of cell movements that drive gastrulation in Xenopus: invagination, involution, convergent extension and epiboly. At the dorsal marginal zone, cells change from a columnar shape to become a "bottle cell" and form an invagination. At this invagination, cells begin to involute into the embryo. This site of involution is called the dorsal lip. The involuting cells migrate along the inside of the blastocoel toward the animal cap. This migration is mediated by fibronectin of the extracellular matrix (ECM) secreted by the blastocoel roof. Eventually, cells from the lateral and ventral sides begin to involute to form a ring of involuting cells surrounding the yolk plug. These involuting cells will eventually form the archenteron which displaces and eventually replaces the blastocoel. Cells from the lateral marginal zone migrate toward the dorsal midline and intercalate with the cells there. This causes the dorsal involuting cells to undergo convergent extension. The dorsal cells become the first to migrate along the roof of the blastocoel cavity and form the anterior/posterior axis of the embryo. During the involution of cells, the cells of the animal cap undergo epiboly and spread toward the vegetal pole. Species Xenopus amieti (volcano clawed frog) Xenopus andrei (Andres clawed frog) Xenopus borealis (Kenyan clawed frog) Xenopus boumbaensis (Mawa clawed frog) Xenopus clivii (Eritrea clawed frog) Xenopus fraseri (Frasers clawed frog) Xenopus gilli (Cape clawed frog) Xenopus laevis (African clawed frog) Xenopus largeni Xenopus longipes (savannah clawed frog... There are very few or no other articles that link to this one. ...


Fish

At the time of mid-blastula transition, the zebrafish embryo is composed of three distinct cell layers: the enveloping layer (EVL), deep cells, and the yolk syncytial layer (YSL) formed from the fusion of cells adjacent to the yolk cells. Binomial name Danio rerio (Hamilton-Buchanan, 1822) The Zebra Danio or Zebrafish (Brachydanio rerio or Danio rerio) is a tropical fish belonging to the minnow family (Cyprinidae). ...


The first stage of gastrulation begins with the epiboly of the EVL and the deep cells over the YSL. This epiboly is driven by the migration of nuclei and cytoplasm in the YSL and attachments between the YSL and the EVL. Intercalation of the deep cells with the EVL help drive this movement. At about 50% of epiboly, a fate map similar to that of the Xenopus can be derived. The EVL develops into an extraembryonic membrane and does not contribute to the embryo.


The second stage of gastrulation occurs when the leading edge of the epibolizing blastoderm thickens. The dorsal side forms a larger thickening and is known as the embryonic shield. The deep cells in the embryonic shield form two layers. The epiblast forms near the surface and will give rise to the ectoderm. The hypoblast forms next to the YSL and will form a mixture of endoderm and mesoderm. The hypoblast is formed through involution and/or ingression. The movement of cells in the hypoblast are similar to the involuting mesoderm of amphibians. The end result of gastrulation is an asymmetric involution of cells that form the dorsal structures of the embryo.


Birds

After cleavage, the blastoderm of chick embryos that sits above the yolk secretes fluid into the basally into the space between the yolk and the blastoderm called the subgerminal space. The region of the blastoderm above the subgerminal space is called the area pellucida. The region of the blastoderm above the yolk is the area opaca. The region where these two zones meet is called the marginal zone. At the posterior marginal zone (PMZ), there is a condensation of cells that is important in gastrulation. Within the PMZ, there is another thickening of cells called the Koller's sickle. Before gastrulation begins, the blastoderm forms two layers: the epiblast and the hypoblast. The epiblast gives rise to the embryo and some of the extraembryonic structures while the hypoblast contributes entirely to the extraembryonic membranes. The hypoblast comes from the primary hypoblast which delaminate out of the epibl This structure is equivalent to the organizer in amphibians and the embryonic shield in fish. Cells ingress through the primitive groove into the blastocoel cavity, migrate anteriorly through Hensen's node and then laterally through the rest of the groove. Cells that are fated to become the endoderm migrate to the bottom of the cavity and replace the hypoblast cells. Cells that are fated to become mesoderm remain in between the future endoderm cells and the epiblast and the epiblast cells remain to become ectodermal cells. The ectoderm, however, is undergoing epiboly to surround the yolk mass. The cells at the edge of the area opaca send out long filopida that attach to fibronectin in the vitelline membrane surrounding the embryo and yolk mass and pull the ectodermal cells toward the vegetal pole. This article or section does not adequately cite its references or sources. ...


As gastrulation proceeds, the primitive streak regresses posteriorly with pharyngeal endoderm, the head process, and the notochord being laid down as it recedes. This results in a temporal gradient of development with the anterior forming organs while the posterior is still going through gastrulation.


Mammals

Prior to gastrulation, the embryo and embryos implants in the uterus. The blastocyst hatches from the zona pellucida at about the time it enters the uterus (zona hatching). The trophoblast cells attach to the endometrial cells of the uterus by adhering to extracellular matrix molecules such as fibronectin, collagen, hyaluronic acid, and heparan sulfate receptors. After contact, the cells directly in contact with the endometrium fuse to form syncytiotrophoblast while the remaining trophoblast cells are called cytotrophoblast cells. The syncytiotrophoblast cells produce enzymes that allow for the invasion of the embryo into the uterine wall and to induce the necessary changes in the uterine tissue. The inner cell mass, meanwhile, divides into two layers: the epiblast and hypoblast. The hypoblast spreads out and covers the blastocoel to form the yolk sac. The yolk sac is an extraembryonic tissue that produces blood cells similar to the structure that surrounds the yolk in birds. The epiblast further divides into two more layers. The amnion layer forms the fluid filled cavity to surround and protect the embryo during pregnancy. The embryonic epiblast undergoes gastrulation. Zona hatching is a phenomenon occuring during prenatal development. ...


Gastrulation in mammals is similar to that in birds with the formation of the primitive streak and Hensen's node and the ingression of cells through the primitive groove to form the endoderm and the mesoderm. During gastrulation, extraembryonic mesoderm forms within the hypoblast or embryonic mesoderm and migrates out to form the blood vessels of the chorion and connect the chorion to the embryo through the umbilical cord.


External links

  • Gastrulation Animations
  • Human gastrulation 3D animation : [1]

  Results from FactBites:
 
Gastrulation (306 words)
Gastrulation includes a series of morphogenetic movements that re-arrange the animal embryo and and result in the establishment of the primary "germ layers" from which tissues will develop and differentiate.
This time-lapse sequence of the dorsal lip formation during early gastrulation in Xenopus (seen from the vegetal pole) was taken by students of the Developmental Biology lab at the University of Utah.
This time-lapse sequence of the gastrulation in Xenopus (seen from the vegetal pole) was taken by students of the Developmental Biology lab at the University of Utah.
Gastrulation - Wikipedia, the free encyclopedia (1803 words)
At the beginning of vertebrate gastrulation, the embryo is a hollow ball of cells known as the blastula, with an animal pole and a vegetal pole.
This epiboly is driven by the migration of nuclei and cytoplasm in the YSL and attachments between the YSL and the EVL.
Gastrulation in mammals is similar to that in birds with the formation of the primitive streak and Hensen's node and the ingression of cells through the primitive groove to form the endoderm and the mesoderm.
  More results at FactBites »

 
 

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