Fig. 2. Defects in the neural epithelium and notochord of chato embryos. Wild-type (A,C,F,I), chato (B,D,E,G,J) and Lp mutant (H) mouse embryos at E8.5 were assayed by in situ hybridization with markers expressed at rhombomeres 3 and 5 (Krox20; A,B, dorsal and ventral views, respectively), neuroepithelia (Sox2; C-E, ventral views), somites (Meox1; F-H, transverse sections) and notochord (T; F-H, transverse sections; I,J, posterior and ventral views, respectively). In some chato mutants, parts of the neuroepithelium remained open (arrowhead in D), giving the neural tube a wavy appearance. Transverse sections in F-H were hybridized with probes for both T (arrowheads) and the somitic marker Meox1 (arrows). In chato mutants, the notochord was embedded in the mesendoderm layer (arrowhead in G) and never formed an individualized rod (arrowhead in F). The notochord of Lp mutants is wider than that of wild-type embryos (F-H, arrowheads) (Greene et al., 1998). Expression of T in chato mutants (J) shows areas where the notochord was wider (w), thinner (t) or absent (a) as compared with wild-type embryos (I, arrowhead). NT, neural tube; not, notochord; r3, rhombomere 3; r5, rhombomere 5; som, somitic mesoderm.