Patterning the pharyngeal arches

The presence of a muscularised pharynx with skeletal support is a fundamental vertebrate characteristic. Developmentally, the pharynx arises from the pharyngeal arches on either side of the head of vertebrate embryos. The development of the pharyngeal arches is complex involving a number of disparate embryonic populations, ectoderm, endoderm, neural crest and mesoderm, which must be co-ordinated to generate the components and overall identity of each of the arches. Previous studies suggested that it is the neural crest that plays a pivotal role in patterning the pharyngeal arches. It is now also becoming clear, however, that there are crest-independent patterning mechanisms. Therefore, pharyngeal arch patterning is more complex than was previously believed and there must be an integration of crest-dependent and -independent patterning mechanisms. BioEssays 23:54-61, 2001.