Practice question

Competence describes tissue ability to respond to an inducer. In presumptive lens ectoderm, Pax6 is expressed well before optic vesicle contact as part of preplacodal region specification by Six1, Eya1. It remodels chromatin and directly binds to enhancers of FoxE3, Sox2 and crystallins, keeping them poised. Upon arrival of BMP4 and FGF signals from optic vesicle, Pax6-positive ectoderm rapidly transcribes lens genes. Pax6 does not itself provide inductive signal nor inhibit BMP, but creates responsive state. Conditional removal from surface ectoderm blocks lens despite intact signaling center.