Practice question

Requirement of BMP in digit patterning was revealed by manipulating BMP antagonists experimentally. Overexpressing Gremlin1 or Noggin throughout digit plate in chick via RCAS retrovirus blocked BMP2-4-7 signaling, preventing both apoptosis in interdigital regions and chondrogenic condensation of phalanges, resulting in webbed, fused and truncated digits with reduced phalanges and syndactyly. Conversely, ectopic BMP application induces apoptosis and digit loss. Wnt7a knockout ventralizes dorsal limb, ZPA graft duplicates AP pattern, early AER removal truncates PD axis. Hence Gremlin overexpression experiment proved BMP necessity for digit formation and separation.