Development

Making a Beak

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Science  18 Apr 2003:
Vol. 300, Issue 5618, pp. 397
DOI: 10.1126/science.300.5618.397a

Development of complex body structures such as the face poses the question of how patterns are formed during embryogenesis. One organizing principle presumes that neural crest cells, the precursors of specific tissues such as the craniofacial mesenchyme, have a predetermined fate. Yet neural crest cells also display remarkable plasticity in response to experimentally manipulated external signals.

Hu et al. addressed the underlying mechanism of facial patterning by examining how a bird's beak attains its specific three-dimensional organization. Fate mapping of cells and gene expression analysis of the early chick embryonic frontonasal process (FNP), the region that gives rise to the face and beak, revealed that before the arrival of neural crest cells, a distinct dorsoventral axis is established. Transplantation of this frontonasal ectodermal zone (FEZ) from quail to chick embryos resulted in additional dorsoventral boundaries and the outgrowth of extra ectopic upper beak structures at the graft site in an orientation-dependent manner. Ectodermal signals from the FEZ could thus override any prepatterning in neural crest cell-derived mesenchyme of the FNP. This challenges the belief that the neural crest is the source of patterning information in the face and demonstrates the responsiveness of neural crest-derived tissue to local patterning cues.—LDC

Development 130, 1749 (2003).

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