Optic cup and lens development requires Pax6 expression in the early optic vesicle during a narrow time window

Pax6 mutations cause complex ocular malformations, but it is uncertain whether early eye development normally requires Pax6 function in both the optic vesicle (OV) and the lens epithelium, or only in the latter. To investigate this question, we electroporated the OV with anti-Pax6 or control morpholinos before the onset of lens placode formation. Pax6 downregulation was already detectable in the OV 10 h after anti-Pax6 treatment, and was accompanied by a significant increase in the death of OV cells. A small eye-like phenotype developed thereafter, whose severity was developmental stage-dependent. When treatment was applied at Hamburger Hamilton (HH) stage 10, there was no optic cup formation, and lens development was abortive despite normal Pax6 expression in the lens epithelium. Treatment at HH stage 11 resulted in structurally normal lens and optic cup, although the latter showed abnormal expression domains for several transcription factors. Early eye development therefore requires cell-autonomous Pax6 function not only in the lens but also in the optic vesicle, where it plays a hitherto unknown role in cell survival. The results, moreover, indicate that there is a critical stage during which Pax6 expression in the OV is necessary for normal lens development.