Fig. 4. Expression and distribution of differentiation markers in Pax6^EE/EE mice. All panels show fluorescently labeled 4 µm paraffin sections counterstained with Hoechst 33258 to indicate nuclei (blue labeling). E11.5 eyes from wild-type (A), Pax6^+/EE (B) and Pax6^EE/EE (C) embryos labeled with anti--crystallin antibodies. Pax6^EE/EE embryos show reduced per cell labeling and a smaller number of positive cells in the posterior lens vesicle. -crystallin labeling at E12.5 of wild type (D), Pax6^+/EE (E) and Pax6^EE/EE (F) embryos emphasizes that there are fewer positive cells in the lens of the homozygous mutant. E11.5 eyes from wild-type (G), Pax6^+/EE (H) and Pax6^EE/EE (I) embryos labeled with anti-ß-crystallin antibodies. Pax6^EE/EE embryos show a reduced level of labeling on a per cell basis and fewer positive cells in the posterior lens vesicle. This indicates a suppression of fiber cell differentiation consistent with morphological findings. This observation is emphasized in comparing wild type (J), Pax6^+/EE (K) and Pax6^EE/EE (L) E12.5 embryos where primary fiber cell extension is minimal in the homozygous mutant.