Practice question

During late gastrulation, vegetal endoderm undergoes vegetal rotation, an autonomous movement where large yolky cells spread and rotate inside blastocoel. This pushes pharyngeal endoderm, which expresses Xhex and Cerberus, forward along blastocoel roof toward animal pole. Pharyngeal endoderm contacts head mesoderm, facilitating head induction through secreted antagonists Dickkopf, Cerberus, and Frzb. Unlike involution driven by IMZ, vegetal rotation is endoderm-driven, displacing blastocoel and positioning foregut precursors anteriorly for proper gut patterning and archenteron elongation, essential for complete digestive tract formation.