(2) Amniotes, such as chick and mouse, form a trough-like structure termed the primitive-streak that runs centripetally from the margin to the center of the embryo. Classically, vertebrates are subdivided into two major categories: (1) Anamniotes such as fish and amphibians form a circumferential blastopore at the site of gastrulation where the superficial (epiblast) cells undergo involution, moving as a sheet that bends inward. During this process morphogenetic movements drive the internalization of prospective mesoderm and endoderm cells from the epiblast, forming a three-layered embryo from a single epithelium.ĭespite the critical importance of this event during development, the morphogenetic re-arrangements that drive gastrulation have changed substantially during vertebrate evolution. Gastrulation is the developmental process that establishes the three definitive germ layers, thereby laying down the foundations of the body plan. This strategy stands mid-way between Anamniotes and Avians/Mammals, suggesting that blastoporal plate is a precursor of the avian primitive streak. Conclusions: Our analysis suggests that reptile gastrulation is bi-modal primary internalization occurs anteriorly by means of an incomplete blastopore-like opening, while posteriorly the cells undergo ingression in the Brachyury-expressing blastoporal plate. We analysed the expression pattern of core mesodermal markers Brachyury and Fgf8 and complimented this analysis with that of the turtle, Trachemys scripta. Results: We analysed early to late gastrulation stages of Chamaeleo calyptratus, showing their unique morphology through confocal imaging of F-actin and laminin-stained embryos to visualise cell morphology and assess basal lamina integrity. Investigating gastrulation in a wider range of Amniotes provides a way to understand evolutionary transition from blastopore to the primitive streak. However, within the Amniote clade there exists a more diverse range of gastrulation strategies than just the primitive streak. How this midline, ingression-based strategy of gastrulation evolved from the ancestral blastopore, a circumferential involution event in Anamniotes, is unknown. North Holland, Amsterdam, The Netherlands.Background: Amniote gastrulation is often described with respect to human, mouse and chick development by the presence of the primitive streak, a posterior-to-anterior midline morphological cell ingression feature that has come to define Amniote gastrulation. (1997) Head induction by simultaneous repression of Bmp and wnt signalling in Xenopus. Glinka, A., Wu, W., Onichtchouk, D., Blumenstock, C., and Niehrs, C. (1997) Structurally related receptors and antagonists compete for secreted wnt ligands. (1991) Overexpression of a homeodomain protein confers axis-forming activity to uncommitted Xenopus embryonic cells. (1989) Interaction between peptide growth factors and homeobox genes in the establishment of antero-posterior polarity in frog embryos. (1994) The Einsteck-method: position and structure of projections formed by implants of a ventral character. (1996) The vertebrate organizer: structure and molecules. This process is experimental and the keywords may be updated as the learning algorithm improves. These keywords were added by machine and not by the authors. However, the Einsteck can be also carried out with heterologous material, cell pellets, and injected animal caps ( 3, 4) and is more versatile than the organizer transplant. While the Einsteck is much easier to perform than the organizer transplant, the position of the implant can be less well controlled, which needs to be considered when interpreting the results ( 2). This results in the formation of an induced structure which, depending on the embryonic stage of the upper blastopore lip, is a head, trunk, or a tail. Organizer activity is revealed either by transplantation of the upper dorsal blastopore lip into the ventral side of a host gastrula or by inserting the tissue into the gastrula blastocoel (Einsteck method). Its two major inducing activities are neural induction and dorsalization of ventral mesoderm differentiation. The amphibian organizer corresponding to the upper dorsal blastopore lip of the early gastrula, is one of the classical systems in which embryonic patterning has been studied ( 1).
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