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Fig. 6 Interdependence of edn1 and ednrA in the ectoderm. Lateral views of whole-mount RNA in situ hybridizations (A-D). In B and D, mutants were identified as 25% of the embryos showing a distinct phenotype. (A) ednra1 is expressed in cranial NC cells of the arches. (B) In suc;edn1-/-, ednra1 is reduced in the ventral mandibular and hyoid arches (arrows). (C) ednrA2 is also expressed by cranial NC cells and is similarly reduced in suc;edn1-/- (D, arrows). (E) A transverse cryosection through the arch shows that edn1 is expressed in endoderm, mesoderm and ectoderm (arrows). (F) In Ednra1 morphants, edn1 is reduced in the pharyngeal ectoderm, although expression persists in the mesoderm (arrows).