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The marginal zone of a chick embryo contains cells that will contribute to the streak. [8] This region has a defined anterior-to-posterior gradient in its ability to induce the primitive streak, with the posterior end having the highest potential. [16]
In chick embryos, early cleavage forms an area opaca and an area pellucida, and the region between these is called the marginal zone. [5] Area opaca is the blastoderm's peripheral part where the cells remain unseparated from the yolk. It is a white area that transmits light. [5]
Gastrulation in frogs commences in the marginal zone— the region encircling the blastula's equator where the animal and vegetal hemispheres meet—differing from sea urchins where it begins in the most vegetal part. In contrast to the vegetal blastomeres, the endodermal cells in the marginal zone of frogs are smaller and contain less yolk. [2]
The marginal zone, however, can give rise to most structures in the embryo including mesoderm. A series of experiments by Pieter Nieuwkoop showed that if the marginal zone is removed and the animal and vegetal caps placed next to each other, the mesoderm comes from the animal cap and the dorsal tissues are always adjacent to the dorsal vegetal ...
Cells in marginal zones of the embryo, like the PMZ, are key to development and cell fate determination in chick embryos. Avian gastrulation occurs as cells move though the primitive streak. Hence, primitive streak is analogous to the blastopore lip in amphibian gastrulation. [ 2 ]
These tissues exist within the involuting marginal zone (IMZ) of the embryo which lies between the vegetal endoderm and the posterior neural tissue. The IMZ is integral to gastrulation and R. Keller et al. eloquently exemplify the importance of convergent extension in Xenopus gastrulation. “…the IMZ, true to its name, involutes or rolls ...
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. [7] In the mammalian blastocyst there are three lineages that give rise to later tissue development.
A typical frog embryo, incubated at 18 °C, is an early stage neurula by 50 hours post-fertilization and a late stage neurula by 67 hours. [3] The mouse embryo begins neurulation on day 7.5 of gestation and remains in the neurula stage until day 9.