Gastrulation


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Gastrulation

The formation of the primordial gut, the archenteron, or digestive cavity of an early animal embryo. More generally, and originally, the term gastrulation referred to the process by which the gastrula stage of the embryo is formed. Thus to nineteenth-century embryologists, gastrulation was the process by which the single-layered blastula, a hollow ball of cells, is converted into the double-layered gastrula. The term has now come to have a still more general meaning, namely, the process by which the three germ layers, or primordial tissues of the embryo, are brought into the positions and relations characteristic of the late gastrula stage, with ectoderm (outer skin), mesoderm (middle skin), and endoderm (inner skin) from the outside to the inside. The terms epiblast, mesoblast, and hypoblast are also used to denote ectoderm, mesoderm, and endoderm, respectively. See Blastulation

Two general but not mutually exclusive methods of gastrulation have been recognized: epiboly and emboly. Epiboly is the growing or extending of one part, such as the upper hemisphere of a spherical blastula, over and around another part, such as the lower hemisphere. Emboly is the pushing or growing of one part into another. In many embryos, both types of cell movement may occur; in certain invertebrate embryos, one type may predominate almost to the exclusion of the other. Generally speaking, epiboly tends to be the major, but not the only, method of gastrulation in forms with large, yolky eggs. See Germ layers

Gastrulation

 

the process in the early embryonic development of multicellular animals that leads to the formation of an embryo with a two-layered and later, in the majority of animals, to a three-layered body wall. Complex shifts of cellular material occur during gastrulation; as a result, part of that material enters the interior of the previously single-layered embryo and lines its wall, which consequently becomes two-layered.

Four basic means of gastrulation are distinguished. Invagination, or intrusion, is the process by which the wall of a one-layered embryo gradually turns inward and forms an internal layer. In epiboly, or overgrowth, relatively large cells rich in yolk are overgrown by the small ones and find themselves inside, forming an internal layer. In immigration, or settlement, certain cells move to the interior of the embryo and settle under the superficial layer; immigration may be unipolar (settlement from one place) or multipolar (from various places). Delamination is the process in which the cells split transversely, converting the one-layered wall of the embryo to a two-layered one. Gastrulation by delamination and immigration is found mainly in coelenterates. In the majority of animals a combination of means of gastrulation occurs, predominantly by invagination and epiboly but also by immigration. The greater the yolk content of an egg, the longer the epibolic process.

In echinoderms, tunicates, acraniates, and lower vertebrates (cyclostomes, fishes, and amphibians), gastrulation generally proceeds in the following manner: the material that actively turns inward in the process of gastrulation forms the covering of the primitive gut, or the dorsal portion of the internal layer, and subsequently, separating from the rest of itself, forms the middle germ layer, the mesoderm. The more passive material forms the base of the primitive gut. Gradually the cells of the base undergrow the material of the covering of the primitive gut and, joining together, close the cavity of the definitive gut. Thus, the two-layered embryo is converted to a three-layered one (the so-called enterocoel method of mesoderm formation).

In higher vertebrates (reptiles, birds, and mammals), the endoderm forms first and does not include material of the future middle layer. The latter separates from the outer layer and is disposed between the ectoderm and the endoderm. In protostomia (worms, mollusks, and arthropods) the mesoderm is formed by the proliferation of certain isolated cells, teloblasts (so-called teloblastic mesoderm formation), whose derivatives position themselves between the ectoderm and the endoderm. The modes of gastrulation, including formation of the mesoderm, are extremely varied and are often very complex.

T. A. DETLAF

gastrulation

[‚ga·strə′lā·shən]
(embryology)
The process by which the endoderm is formed during development.
References in periodicals archive ?
Petryk et al., "The function of twisted gastrulation in regulating osteoclast differentiation is dependent on BMP binding," Journal of Cellular Biochemistry, vol.
Pawson, "Morphogenetic movements at gastrulation require the SH2 tyrosine phosphatase Shp2," Proceedings of the National Academy of Sciences of the United States of America, vol.
To define the three groups, the authors do not use reasons sustained in comparisons between mice and humans but the cell movements during gastrulation leading to a natural result of the process of cellular differentiation and the establishment of three distinct lineages of stem cells, during the embryogenesis period.
During gastrulation, the mesoderm that has moved into the embryo is positioned in the block side of the notochord, a structure that supports the spinal cord and extends from head to tail in a central position (Paes, 2008).
Dorsal midline fate in Drosophila embryos requires twisted gastrulation, a gene encoding a secreted protein related to human connective tissue growth factor.
(2009) Essential role of O-1,4-galactosyltransferase 2 during medaka (Oryzia latipes) gastrulation. Mech.
The development of the nervous system can be divided into three stages: gastrulation, primary neurulation and secondary neurulation.
Laminins (LN) are components of all basement membranes, specialized extracellular matrices found throughout the bodies of vertebrates and invertebrates, with diverse roles in fundamental developmental processes such as epiblast polarization and gastrulation, as well as in organ development and function [22, 23].
Moreover, in the endocardial lineage, Delta 4, Notch 1, and Notch 4 transcription begins at early gastrulation, while HRT 1 and HRT 2 are expressed in the endocardium or myocardium at various stages of cardiac development (14).
Drastic expression change of transposon-derived piRNA-like RNAs and microRNAs in early stages of chicken embryos implies a role in gastrulation. RNA Biol.
Relative to unselected cells, AHR-positive cells showed a time-dependent decrease of expression of GO categories involved in a) cardiac differentiation and morphogenesis, b) increasingly lower expression of categories involved in WNT (wingless-related MMTV integration site 3A) signaling and regulation of gastrulation, c) gametogenesis, and d) high levels of expression of genes involved in drug and xenobiotic metabolism (Figure 2B; see also Supplemental Material, Table S3).
Skourides explained that to determine the role of FAK, they generated a novel inhibitor which is very effective in blocking FAK's function, allowing them for the first time to probe the role of FAK during gastrulation.