The segmentation of the vertebrate body is established by somitogenesis, during which somite form sequentially in a rhythmic fashion from the paraxial presomitic mesoderm. The somites are transient embryonic segments giving rise to the vertebras, the skeletal muscles and dorsal epidermis. In vertebrates, all cells of the paraxial mesoderm go successively through the three phases of differentiation and matura- tion, which are tightly regulated at the spatio-temporal level.