Practice question

In Xenopus, archenteron elongation depends on convergent extension and active migration of deep cells of involuting marginal zone. These internal mesodermal cells undergo mediolateral intercalation using planar cell polarity Wnt pathway, fibronectin, and C-cadherin, pushing tissue anteriorly. Removal of deep IMZ while leaving superficial epithelial layer and bottle cells intact allows initial invagination but archenteron fails to elongate, remaining short pit. This demonstrates deep IMZ provides force for vegetal rotation and extension. Animal cap and vegetal pole cells alone cannot drive elongation.