RESTORATION OF NORMAL HOX CODE AND BRANCHIAL ARCH MORPHOGENESIS AFTEREXTENSIVE DELETION OF HINDBRAIN NEURAL CREST

Among the derivatives of the cephalic neural crest is the ectomesenchy me which subsequently constitutes most of the craniofacial skeleton. T here is evidence to suggest that the skeletogenic fate of the hindbrai n neural crest is specified before emigration from the neural tube and that Antennapedia class Hox genes are involved in that process. To ex plore the putative causal link between Hox expression and craniofacial morphology, we produced a specific series of bilateral crest deletion s in chick embryos and assessed branchial arch morphology, Hox gene ex pression, and patterning of skeletal structures in the postoperative e mbryo. Surprisingly, we found that deletion of the bulk of the rhomben cephalic crest and substantial portions of the dorsal rhombencephalon did not prevent normal branchial arch morphogenesis and normal pattern s of Hox gene (-A3 and -B4) expression 48 h after operation. Neural cr est-like cells have been identified on crest migration pathways at the level of the original ablation, further confirming that ablated cepha lic neural crest is replaced by regeneration from the cut edge of the neuroepithelium. Furthermore, in such embryos ectomesenchyme from rege nerated crest is able to form a facial skeleton in which the mandible and hyoid apparatus are normal in size and organization. These finding s demonstrate that the cranial neuroepithelium has more extensive rege nerative capacities than was previously thought, which has important i mplications for investigations of craniofacial development. (C) 1995 A cademic Press, Inc.