Practice question

Interaction between optic vesicle and lens placode represents classic example of reciprocal induction where each tissue signals back to refine other. Optic vesicle secretes BMP4 and FGF8 inducing lens placode thickening, expression of Sox2, L-Maf, and delta-crystallin, placode invaginates into lens vesicle. Lens placode then secretes FGFs and retinoic acid inducing optic vesicle to invaginate into bilayered optic cup and pattern retina versus retinal pigment epithelium. Conditional induction describes stepwise competence, autonomous specification lacks signals, morphogenetic movement alone does not explain molecular interchange inherent in reciprocal induction and coordination.