Practice question

Amphibian gastrulation integrates three movements: epiboly expands animal cap ectoderm over entire embryo via radial intercalation; involution rolls marginal zone mesoderm inside over blastopore lip; invagination and involution driven by bottle cells create archenteron cavity. Convergent extension of dorsal mesoderm narrows and elongates body axis through mediolateral intercalation regulated by non-canonical Wnt planar cell polarity pathway. These coordinated morphogenetic events occur without large growth, reshaping blastula into gastrula with internalized mesoderm and endoderm and dorsal organizer positioned for subsequent neural induction and patterning of body plan.