Question

Describe the gastrulation movements in amphibians that involve a) the epiboly of the ectoderm and b) the involution of the mesoderm

Answer 1

Gastrulation is the process of changing the embryo from a blastula with a single layer of cells to a gastrula containing multiple layers of cells. Gastrulation of amphibians begins with the invagination movement of the bottle cells, followed by the coordinated involution of the mesoderm and the epiboly of the ectoderm.

a) the epiboly of the ectoderm- epiboly is a type of cell movement in which a layer of epithelial cells spreads. During amphibian gastrulation, the animal cap and the non involuting marginal zone cells expand by epiboly to cover the entire embryo. These cells will form the surface ectoderm. In Xenopus laevis (an amphibian) epiboly leads to an increase in number of cells (due to division) coupled with a concurrent integration of several deep layers into one. Also, cause assembly of fibronectin into fibrils by the blastocoel roof.

b) the involution of the mesoderm- Involution is a type of cell movement during gastrulation which involves the inturning or inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining cells. Gastrulation in amphibians is initiated by the formation of bottle cells at the dorsal marginal zone followed by the involution of prospective mesodermal cells. The mesoderm and endoderm then migrate along the blastocoel roof. Gastrulation movements in amphibian embryos act to position the mesoderm in between the outer ectoderm and inner endoderm. These movements are initiated on the future dorsal side of the embryo, just below the equator in the region of the gray crescent.