Fig. 6. Pax6 is required for initiating and maintaining the expression of the nasal and temporal retinal determinants BF-1 and BF-2. Radioactive situ hybridization of 6 µm horizontal sections. (A) In wild type at E12.5, BF-1 is expressed in the nasal (ns) NR and in the olfactory epithelium (oe), as well as the telencephalon (see C), while BF-2 is detected in the temporal (tm) NR (B). (C) In Pax6^–/– embryos, no BF-1 can be detected in the optic vesicle (open arrowheads), but normal levels in the telencephalon (tel) and low levels in the neuroepithelium around the chiasm (asterisk). (D) Likewise, no BF-2 expression is detectable in the Pax6^–/– optic vesicle, while normal levels are found in the surrounding mesenchyme (white arrowhead). (E,F) Absence of retinal BF-1 (E) and BF-2 expression (open arrowheads) after conditional Pax6 inactivation in the distal NR of E14.5 -Cre; Pax6^flox/flox embryos. Normal levels of BF-1 are still detected in the oe (E), as well as normal BF-2 levels in the dura mater surrounding the optic nerve (F, white arrowhead). Note that in E and F, signal in the lens is due to reflection of lens fibers in dark-field microscopy. (G) In the wild-type embryo, Tbx5 is expressed specifically in the dorsal NR, while Tbx5 fails to be expressed in the Pax6^–/– optic vesicle (I). Vax1 whose expression at E12.5 is found in the very ventral NR (H), is expressed throughout the whole Pax6^–/– optic vesicle (J). le, lens; nr, neural retina; ov, optic vesicle; rpe, retinal pigmented epithelium; ch, chiasm.

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