Pax6 maintains lens epithelial cell identity and coordinates secondary fiber cell differentiation

Pax6 is a crucial regulator of vertebrate eye development, and its loss leads to the failure of lens placode formation. To investigate Pax6 function at successive stages of lens development, we employed the Cre-loxP system in combination with a novel Foxe3-Cre driver, which becomes active after the lens placode stage but prior to the onset of secondary fiber cell differentiation. The Foxe3-Cre enables efficient deletion of Pax6 throughout the entire lens by embryonic day E12.5. Our study shows that Pax6 loss causes a delay in lens differentiation, disrupts the lens epithelium, and produces a smaller lens that remains attached to the cornea, ultimately leading to a rudimentary lens in adulthood. Notably, Foxe3 persisted in the mutant lens epithelium despite Pax6 loss, while apoptosis and aberrant Sox2 upregulation occurred in the epithelium. Combined with the delayed onset of fiber cell differentiation, the abnormal anterior expansion of fiber cell differentiation regulators (c-Maf and Sox1), and the aberrant expression of cyclin D2, these results underscore the essential role of Pax6 in preserving lens epithelial identity and coordinating the transition to secondary fiber cell differentiation.