Vertebrate jaw development is a complex process and it is unclear how the neural crest cells in the pharyngeal arches, which give rise to the facial skeleton, are patterned. Haworth and co-workers use fate mapping to show that in chick the first patterning process in jaw morphogenesis occurs in the developing head ectoderm before neural crest formation (see p. 4797). The spatial expression of developmental genes in the mandible primordium is regulated by the spatially restricted expression of signalling factors in the overlying oral epithelium, which is formed by ectodermal and endodermal cells. The researchers show that the cells fated to occupy the proximal Fgf8-expressing and distal Bmp4-expressing domains of the oral ectoderm at stage 18-20 of development are already localised to specific ectodermal regions by stage 8. This regionalisation is regulated by the endoderm. Similar early prepatterning of the orofacial epithelium is likely to be conserved...

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