Sox1 heterozygosity increases the number of fiber cells in Pax6Sey/+ lenses. E-cadherin immunofluorescence (red) and DAPI nuclear stain (blue) are shown (A–D) for wild-type (A), Sox1+/− (B), Pax6Sey/+ (C) and Pax6Sey/+, Sox1+/− (D) lenses at E13.5. (E) E-cadherin negative, fiber cell nuclei were counted for wild-type (white box), Sox1+/− (light grey box), Pax6Sey/+ (black box) and Pax6Sey/+, Sox1+/− (dark grey box) lenses and the number of fiber cell nuclei in Pax6Sey/+, Sox1+/− lenses is statistically significantly higher than those in Pax6Sey/+ lenses (see Experimental Procedures).