Fig. 6. Maternal dietary RA supplementation rescues r3/r4 and r4/r5 gene expression boundaries in Raldh2^–/– embryos. Embryos were subjected to low-dose maternal dietary RA supplementation from E6.75-E8.0 (A,F-H) or from E6.75-E8.25 (B-E). (A) RARE-lacZ expression in RA-treated wild-type and Raldh2^–/– embryos at E8.0. The Raldh2^–/– embryo exhibits an anterior border of RARE-lacZ expression similar to that observed in a wild-type littermate, although the intensity of staining was less than that observed in the wild-type embryo. (B-E) RA treatment of wild-type and Raldh2^–/– embryos followed by analysis at E8.75 demonstrates that RA administration rescues r4 expression of Hoxb1 (B,C) and Cyp26c1 (D,E) in Raldh2^–/– embryos. RA-treated wild-type embryos exhibited relatively normal expression of Hoxb1 and Cyp26c1. All embryos were also simultaneously stained for Raldh2 expression, which appeared only in wild-type embryos as indicated. (F-H) RA treatment of Raldh2^–/– embryos followed by analysis at E8.0 results in posterior hindbrain expression of vHnf1 (F-G) and relatively normal r4/r5 restriction of Irx3 (H). Embryos were double stained for Raldh2 expression, which was observed only in wild-type embryos (brackets).