Pax6 is misexpressed in Sox1 null lens fiber cells.

Sox1 null lens fiber cells fail to elongate and have disrupted expression of gamma-crystallin. We have evaluated the expression of Sox1 and Pax6 proteins during critical stages of lens morphogenesis, with particular focus on fiber cell differentiation. While Pax6 and Sox1 are co-expressed during early stages of fiber cell differentiation, Sox1 up-regulation coincides temporally with the down-regulation of Pax6, and these proteins therefore display a striking inverse expression pattern in the lens fiber cell compartment. Furthermore, Pax6 is inappropriately expressed in the fiber cells of Sox1 null mice and the Pax6 target, alpha5 integrin, is simultaneously misexpressed. Finally, we demonstrate a genetic interaction between Sox1 and Pax6, as Sox1 heterozygosity partially rescues the diameter of Pax6(Sey) lenses by increasing the number of cells in the fiber cell compartment.