Initiation of Gastrulation: Dorsal Blastopore Lip Formation
Gastrulation in Xenopus embryos begins in the marginal zone surrounding the equator of the blastula. More specifically, it is initiated on the future dorsal side of the embryo, about 180 degrees from sperm entry point. Here, the bottle cells invaginate to form a slit-like blastopore. The invagination of the cells initiates archenteron formation.