Figure 2.

Analysis of cranial neural crest cells in wild-type and Zfhx1b-knockout embryos. A and B, Lateral view of the head region of E8.5 embryos hybridized with the Twist probe (Fuchtbauer 1995). Note the reduced Twist mRNA expression in the head mesenchyme and the absence of the first branchial arch (black arrow) in the knockout embryos (B). C and D, Sox10 mRNA expression at E8.5 (lateral view, probe [MMU66141]; bp 1194–2064). In wild-type embryos, Sox10-expressing trigeminal or facial neural crest cells are migrating (red arrow) from the brain plate toward the maxillary component of the first and second branchial arches, respectively, whereas in the knockout embryo the Sox10-positive cranial neural crest cells do not delaminate at the junctional zone between the neural and surface ectoderm. E–H, Radioactive in situ hybridization (according to Dewulf et al. [1995]) for Sox10 in transverse sections taken at the level of the headfolds (E and F) and the heart (at r4) (G and H). The sections show Sox10-positive crest cells that initiated migration in the morphologically wild-type embryos (black arrow in G). In the knockout embryos, Sox10-positive neural crest cells do not delaminate nor do they initiate migration (black arrow in H). I and J, Radioactive in situ hybridization for AP-2 (Zhang et al. 1996) on sections of the midbrain. In wild-type embryos, AP-2 is expressed in ectoderm and in neural crest cells migrating from the cranial neural fold (circle in I). In the Zfhx1b-knockout littermates, AP-2-positive migrating neural crest cells are never seen in this area (circle in J). ba = branchial arches; cnc = cranial neural crest; KO = knockout; WT = wild type.