Practice question

FGFR activation recruits adaptor FRS2α leading to Grb2-SOS complex activating Ras-MAPK cascade, PI3K-AKT survival, plus direct PLCγ calcium release and STAT activation via scaffolds and direct phosphorylation. JAK-STAT pathway becomes engaged via STAT1,3,5 phosphorylation by FGFR kinase activity or associated Jak1/2 kinases, regulating chondrocyte growth arrest and immune genes SOCS3, p21. Although MAPK is primary developmental route for proliferation and patterning, JAK-STAT mediates FGFR3 dwarfism through STAT1 nuclear accumulation inhibiting cell cycle progression via Cip/Kip inhibitors. Wnt/beta-catenin is separate pathway activated by Frizzled, not typical FGF downstream, highlighting overlapping downstream networks sharing effectors.