Practice question

Bone morphogenetic protein activity must be spatially modulated to permit cartilage condensation and prevent premature apoptosis. Noggin is secreted extracellular antagonist binding BMP2, BMP4, BMP7 with high affinity, preventing ligand binding to receptors and Smad activation. Expression of Noggin in distal mesenchyme allows chondrogenic differentiation and maintains FGF signaling loop through Gremlin-family related inhibition. Wnt7a dorsalizes limb, FGF10 induces bud, Tbx5 specifies forelimb. Balanced BMP-Noggin interplay regulates joint formation, digit number, and interdigital regression essential for sculpted limb morphology and digit separation.