Fig. 2. (A-F) Defects in aortic arch formation in RA-rescued Raldh2^–/– embryos. Embryos collected at E9.5 (A,B), E10.5 (C,D) or E11.5 (E,F) were incubated in phosphate-buffered saline and injected intracardially with china ink. Compare the aortic arch patterns in wild-type (A,C,E) and Raldh2^–/– (B,D,F) embryos (see text for details). The inset in F shows a detail of a different Raldh2^–/– embryo. Arrowheads point to the single embryonic vessel connecting the aortic sac and the dorsal aorta. (G-I) Analysis of Raldh2 expression pattern in the wild-type embryonic pharyngeal region. Whole-mount in situ hybridization of an antisense Raldh2 riboprobe was performed on E8.5 (10 somites, G) and E8.75 (16 somites, H,I) wild-type embryos. The arrowhead in G points to Raldh2 expression boundary in the posterior foregut region. (I) A higher magnification of the branchial arch region, viewed from the inside after bisection of the embryo. (J-L) Patterns of RA response in the branchial arch region of E8.5 wild-type (J) and Raldh2^–/– (K,L) embryos carrying a RARE-hsp68-lacZ reporter transgene. Embryos are shown after whole-mount X-gal assay and medial bisection of their head and trunk region (inside views). a2-a6, aortic arches; as, aortic sac; b1-b3, branchial arches; da, dorsal aorta; en, endoderm; ey, eye; fg, foregut; me, mesoderm; nt, neural tube; so, somites.