Practice question

Digit separation requires elimination of interdigital mesenchyme via programmed cell death regulated by bone morphogenetic proteins. BMP2, BMP4, BMP7 are expressed in interdigital regions activating SMAD1/5/8 to induce ROS production, Msx1/2, and apoptotic effectors, while digit condensations express antagonists Gremlin, Noggin, FGFs protecting chondrogenic cells. Blocking BMP signaling with Noggin beads retains webbing causing syndactyly, whereas exogenous BMP widens death zones. FGF8 from digit tips counteracts BMP to fine-tune boundaries. Hence BMP4 constitutes major inducer of interdigital apoptosis sculpting free digits.