Practice question

Reciprocal induction describes mutual signaling where tissue A induces tissue B, and induced tissue B signals back to regulate development of tissue A. In eye, optic vesicle secretes BMP4 and FGF8 inducing overlying ectoderm to form lens placode. Newly formed lens placode and later lens vesicle secrete BMP7, FGF9 and TGFbeta2 that induce distal optic vesicle to fold inward forming optic cup and to pattern inner neuroretina versus outer pigmented epithelium. Classical Spemann experiments and modern molecular ablations confirm removal of either partner arrests both, validating reciprocal dependency central to coordinated vertebrate eye assembly.