The many roles of Notch signaling during vertebrate somitogenesis.

The embryonic vertebrate body axis contains serially repeated elements, somites, which form sequentially by budding from a posterior tissue called the presomitic mesoderm (PSM). Somites are the embryonic precursors of the vertebrae, ribs and other adult structures. Many inherited human diseases are characterized by dysregulated somitogenesis, resulting in skeletal abnormalities that are evident at birth. Several of these conditions, including some cases of autosomal recessive familial spondylocostal dysostosis (SCDO), arise from mutations in the Notch signaling pathway, which has been demonstrated to be a key player in the regulation of somitogenesis. Here, we review the functional roles of the Notch pathway in vertebrate segmentation, focusing on its activities in a clock that times the formation of somites, as well as in the patterning and production of epithelial somites.