Fig. 7. Pharyngeal defects in Chrd^-/- embryos at mid-gestation. (A,A') External view of wild-type (A) and mutant (A') E9.0 embryos; mutants present a fully penetrant phenotype consisting in reduction of the otic vesicle (arrowheads), absence of second (hyoid) pharyngeal arch and a conspicuous indentation in the neck (arrow). (B,B') Whole-mount in situ hybridization of E9.5 embryos with a Sox10 probe that labels glial cells. The trigeminal (tr) and vestibulocochlear (vc) ganglia are deformed and displaced in the mutant (B'). (C,C') Pax3 whole-mount in situ hybridization of E10.5 embryos. Neural crest cells (arrowheads) migrating through the peripharyngeal region into the proximity of the heart (h) are absent in the mutant embryo (C'). md, mandibular component of the first pharyngeal arch; hy, hyoid or second pharyngeal arch; dm, dermomyotomes; fl, forelimb. Abnormal axonal projections from the trigeminal into the vestibulo-cochlear are indicated (arrowhead). The epibranchial placode-derived geniculate (g), petrosal (p) and nodose (n) ganglia are absent in the mutant. ov, otic vesicle; drg, dorsal root ganglia. (D-F') Whole-mount in situ hybridization with Pax9 probe. (D,D') Lateral view of E9.5 wild-type (D) and mutant (D') embryos made transparent with benzyl benzoate. Pax9 pharyngeal expression is reduced in the mutant. pe, pharyngeal endoderm; pg, postanal gut. (E,E') Dorsal view of the same embryos; in the mutant the pharynx is reduced and pharyngeal pouches II, III and IV are absent. (F,F') Lateral view of E10.5 wild-type and mutant embryos. Note the lack of Pax9 expression specifically in pharyngeal endoderm (pe) of the mutant. fm, facial mesenchyme; sc, sclerotome.