Practice question

Fibroblast Growth Factors bind high-affinity Receptor Tyrosine Kinases FGFRs composed of extracellular three immunoglobulin loops, single transmembrane helix, intracellular split tyrosine kinase domain requiring dimerization. Ligand plus heparan sulfate proteoglycan induces dimerization and trans-autophosphorylation of activation loop tyrosines Y653/654 recruiting adaptor FRS2, activating Ras-MAPK, PI3K-AKT, PLCγ calcium release, and JAK-STAT effectors promoting survival, mitogenesis, migration. This RTK nature distinguishes FGF from Hedgehog which uses Patched-Smoothened seven-transmembrane, and Wnt which uses Frizzled-LRP beta-catenin. RTK signaling explains rapid mitogenic effects influencing chondrocyte growth during embryogenesis.