What happens when Pax6 is overexpressed in surface ectoderm?
Pax6 functions as sufficient master regulator for lens program. Misexpression experiments using PAX6 cDNA electroporated into embryonic chick surface ectoderm outside normal eye region, or promoter driven in frog epidermis, activates endogenous Sox2, FoxE3, Maf genes and delta-crystallin, culminating in formation of ectopic lens placodes and lens vesicles with fiber differentiation. This demonstrates that providing Pax6 competence factor can bypass requirement for optic vesicle signal in regions that already possess low levels of BMP and FGF. Thus overexpression converts non-lens ectoderm toward lens fate, confirming key competence role.
Ref: Altmann et al. 1997; Gilbert, Developmental Biology Chapter: Pax6 overexpression induces ectopic lens formation.