Fig. 7. Lack of enteric nervous system development in RA-rescued Raldh2^–/– mutants. In situ hybridization was performed with a ³⁵S-labeled Ret probe on cryosections of wild-type (A,C,E,G,I) and Raldh2^–/– (B,D,F,H,J) embryos. Each panel shows bright-field (left) and dark-field (right) views of the same section to show, respectively, the histology and the in situ hybridization signal (white dots). At E10.5, mutant embryos only show scattered Ret-labeled prospective ganglioblasts (arrows in B), which failed to colonize the midgut levels (compare A and B). E12.5 mutant embryos have rudimentary vagal nerve tracts (compare C and D, arrows) and their stomach and gut wall are devoid of Ret-positive ganglion cells (compare E,G and F,H). Other domains of Ret expression (e.g. in the trigeminal ganglia: compare I and J) are unaffected in mutants. fg, foregut; g5, trigeminal ganglion; mg, midgut; sc, spinal cord; st, stomach; ur, ureteric bud.