Practice question

Lens induction requires fibroblast growth factor signaling synergizing with BMP4 from optic vesicle. FGF family members FGF1, FGF8, and FGF2 activate Ras-MAPK and PI3K pathways in competent head ectoderm enhancing Sox2 and L-Maf expression and promoting placodal proliferation and crystallin synthesis. Hedgehog suppresses eye field centrally, Notch regulates differentiation timing but not primary induction, JAK-STAT influences other tissues. Experimental implantation of FGF beads near embryonic ectoderm induces ectopic lens markers, while FGFR inhibition blocks lens formation, evidencing FGF requirement in lens inductive cascade and fiber differentiation.