Fig. 6. Induction of Raldh1 in dorsal retina of Raldh2^–/– embryos by conditional RA rescue. (A,B) RARE-lacZ expression in the eye of E10.5 Raldh2^–/– embryos treated with RA to E8.25 is shown (A) as a whole-mount stained for only 2 hours and (B) as a frontal section to depict the high level of expression in dorsal retina. (C,D) Combined detection of Raldh1+Raldh2 mRNAs by whole-mount in situ hybridization at E9.75, using both probes simultaneously, for Raldh2^–/– (C) and wild-type (D) embryos treated with RA to E8.25; this shows that the rescued mutant, which has very low Raldh2 mRNA detection relative to wild type, now expresses Raldh1 in the dorsal retina. dr, dorsal retina; ol, olfactory pit; rpe, retinal pigment epithelium.