Practice question
Question
Which gene is essential for lens formation by making the head ectoderm competent?
Explanation
Competence of head ectoderm to form lens is established by transcription factor Pax6, master regulator of eye development expressed early in anterior neural plate and surface ectoderm. Pax6 directly binds enhancers of lens genes Six3, Sox2, and crystallins, rendering ectoderm responsive to BMP and FGF from optic vesicle. Sox2 cooperates with Pax6 but not alone, L-Maf acts later downstream, Rx1 specifies retinal field. Pax6 knockout ectoderm fails to form lens even with wild-type optic vesicle, while Pax6 overexpression confers competence, confirming essential priming function for lens.