Practice question

Gastrulation involution requires dynamic cell-matrix interactions. Fibronectin fibrils assembled on blastocoel roof provide RGD-containing substrate for integrin alpha5beta1 mediated adhesion and migration of involuting marginal zone cells. Fibronectin guides radial intercalation pulling mesoderm inside. Depletion using antisense morpholinos, RGD peptides or antibodies eliminates fibrils, causing mesoderm cells to lose traction, failing to involute over blastopore lip. Blastopore remains open, mesoderm accumulates outside, phenotype described as failed involution without dorsalization or axis duplication, indicating purely mechanical movement defect. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.