Fig. 3. Dorsoventral patterning of the somite is abnormal in Gli2^–/–Gli3^–/– embryos. Transverse sections through the trunk of wild-type (A), and Gli2^–/–Gli3^–/– (B) embryos at E10.5 were stained to reveal tissue morphology. In Gli2^–/–Gli3^–/– embryos, ectopic epithelium extends ventromedially (open arrowheads), the sclerotome is reduced and myotome is not distinguishable. dm dermomyotome, scl sclerotome, my myotome. Expression of Pax3 and Myf5 were assessed by whole-mount in situ hybridization in wild-type (C,E) and Gli2^–/–Gli3^–/– (D,F) E9.5 embryos. Pax3 in Gli2^–/–Gli3^–/– embryos appeared normal in wholemount. Myf5 expression in Gli2^–/–Gli3^–/– somites was diffuse and expanded laterally. Additionally, dorsomedial-specific expression (arrowhead in E) was absent (arrowhead in F). Scale bar: 0.5 mm. (G-R) Expression of Pax3, Sim1, Pax1 and Myf5, were assessed by whole-mount in situ hybridization and sectioned. Transverse sections though the trunks of E.9.5 wild-type (G,I,K,O), Gli2^–/–Gli3^–/– (H,J,L,P), Shh^–/– (M,Q) and Shh^–/–Gli3^–/– (N,R) embryos were collected. Broken lines outline ectopic epithelium in H,J,L,P. In Gli2^–/–Gli3^–/– embryos Pax3 is expressed in the ectopic ventromedial epithelium of Gli2^–/–Gli3^–/– somites (arrowhead in H). Sim1 expression is normal in wild-type (arrowhead in I) and Gli2^–/–Gli3^–/– mutants (arrowhead in J). Pax1 expression is weak in Gli2^–/–Gli3^–/– embryos (L), undetectable in the trunk of Shh^–/– embryos (M), but restored in Shh^–/–Gli3^–/– embryos (N). In wild type, Myf5 is restricted to the layer of myotome (O), whereas in Gli2^–/–Gli3^–/– somites, Myf5 is expressed throughout the mesenchymal cells within the epithelial spheres (P). In Shh^–/– somites, dorsomedial expression of Myf5 is reduced (arrowhead in Q), whereas in Shh^–/–Gli3^–/– somites Myf5 is restored in the dorsomedial lip (R). Scale bar: 50 µm.