Practice question

Wnt planar cell polarity pathway controls polarized cell intercalation, convergence and directional migration after ingression. Inhibition via mutants of Vangl2, Prickle or Dishevelled DEP domain blocks Wnt5a/Wnt8c non-canonical signaling, preventing lateral dispersal of mesoderm and endoderm away from streak midline. Live imaging shows cells remain clustered centrally instead of spreading peripherally to form lateral plate and extraembryonic mesoderm. Phenotype termed centralized mesoderm/endoderm indicates failure of PCP-mediated cell movement, distinct from loss of mesoderm or neural tube formation. Therefore inhibition centralizes mesendoderm. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.