Somitogenesis: segmenting a vertebrate.

The partitioning of the vertebrate body into a repetitive series of segments, or somites, requires the spatially and temporally co-ordinated behaviour of mesodermal cells. To date, it remains unknown how applicable our knowledge of the genetic mechanisms governing Drosophila segmentation will be to that of vertebrates, though recent results indicate some degree of conservation. Genetic studies in the mouse point to a major role for the Notch-Delta signalling pathway in somite formation. Furthermore, a molecular clock may be 'ticking' in the presomitic mesoderm.