Fig. 4. Abnormal distribution of facial neural crest cells in Raldh2^-/- embryos. Whole-mount in situ hybridization of Crabp1 (A,B), Ap2a (C,D), Sox10 (E,F) and Sox9 (G,H). Profile views. Embryos are at 12-14 somites (A-F) or E9.5 (G,H, and insets in C,D). Genotypes are indicated above. Brackets (A,B) indicate a deficit of labeled cells in the post-optic area, and arrows (D,F) indicate an excess of labeled cells in the preoptic (frontonasal) region of mutant embryos. ov, optic vesicle. Insets in A,B show transverse sections of 13- to 14-somite stage embryos.