Practice question

Interdigital cell death is tightly regulated by BMP family members, primarily BMP2 BMP4 BMP7 secreted in interdigital mesenchyme under control of retinoic acid and Msx transcription. BMP binds type I receptors activating Smad1-5-8, inducing Msx2 and proapoptotic genes leading to caspase activation and DNA fragmentation. FGF8 from AER and Gremlin from digit tips normally inhibit BMP to protect digit chondrogenesis driven by Sox9 and Bmpr1b. Manipulating BMP signaling converts free digits to webbed or truncates digits. Wnt7a patterns DV axis, Gremlin antagonizes BMP upstream, but execution depends on BMP ligands.