Practice question

Head ectoderm acquires ability to form lens long before optic vesicle contact, a property called competence. Pax6, a paired-homeodomain transcription factor, marks the entire preplacodal region and maintains chromatin accessible for lens-specific enhancers like FoxE3 and Sox2. Without Pax6, surface ectoderm fails to upregulate crystallins even when grafted with a wild-type optic vesicle. Fujiwara rat recombination experiments showed mutant ectoderm non-responsive, proving Pax6 functions intrinsically in ectoderm competence rather than inductive signal production, enabling subsequent BMP and FGF mediated differentiation.