Pax6 and Sox1 expression are inversely correlated in the developing fiber cell compartment. Wild-type eyes at embryonic day (E) 11.5 (A–C), E12.5 (D–F), E13.5 (G–I), and E15.5 (J–L) with immunofluorescence for Pax6 (red) (A, D, G, J), or Sox1 (green) (B, E, H, K) and DAPI nuclear stain (blue) are shown. Additional sections of Sox1βgeo/+ lenses stained for β-galactosidase activity are shown (C, F, I, L) to highlight Sox1 expression in the AEL. The arrows in C highlight the anterior extreme of β-galactosidase activity. The arrows in panels F, I and L indicate β-galactosidase activity in the AEL. The arrowheads in J and K highlight nuclei positive for Sox1 and negative for Pax6. All eyes (in all figures) are oriented anterior to the right and posterior to the left. Abbreviations: ael anterior epithelial layer, fc fiber cell compartment, lv lens vesicle Scale bars in all figures are 100 microns.