Formation and differentiation of the avian sclerotome

The avian sclerotome forms by epitheliomesenchymal transition of the ventral half-somite. Sclerotome development is characterized by a craniocaudal polarization, resegmentation, and axial identity. Its formation is controlled by signals from the notochord, the neural tube, the lateral plate mesoderm, and the myotome. These signals and crosstalk between somite cells lead to the separation of various subdomains, such as the central and ventral sclerotomes that express Pax1 under the control of Sonic hedgehog and Noggin, and the dorsal and lateral sclerotome that do not express Pax1 and are controlled by Bmp-4. Further subdomains that give rise to specific derivatives are the syndetome, neurotome, meningotome, and arthrotome. The molecular control of subdomain formation and cell type specification is discussed.