Fig. 5. Ectopic neural crest marker gene expression in the dorsal neural tube and mesenchyme cells adjacent to r3 of E9.5 Msx1/2 mutant embryos. (A-L) Dorsal views of embryos analyzed by whole-mount in situ hybridization. (A,B) Expression of Msx1 and Msx2 in E9.5 wild-type embryos. (C-L) Expression of the neural crest markers Ap-2 (C-F), Sox10 (G-J) and cdh6 (K,L) in control (C,E,G,I,K) and Msx1/2 mutant (D,F,H,J,L) embryos at the indicated stages. Note the aberrant expression of each marker at the level of r3 in mutant embryos (arrowheads in D,H,J,L). Intense ectopic expression of Ap-2 in the midline of the dorsal neural tube was also evident in mutant embryos (arrows in D,F). (M-P) Serial sections of Ap-2 stained whole-mount embryos. Ap-2 transcripts in the mutant are located in the mesenchyme adjacent to r3 (arrowhead in P). Arrows in N and P indicate ectopic Ap-2 expression in the dorsal neural tube of the mutant embryo. nc, neural crest; nt, neural tube; ot, otic vesicle. Scale bars: in B (for A,B), D (for C,D), H (for G,H), in L (for K,L), 0.2 mm: in F (for E,F), in J (for I,J), 0.4 mm; in O (for M-P), 50 µm.