The regulation of mesodermal progenitor cell commitment to somitogenesis subdivides the zebrafish body musculature into distinct domains.

The vertebrate musculature is produced from a visually uniform population of mesodermal progenitor cells (MPCs) that progressively bud off somites populating the trunk and tail. How the MPCs are regulated to continuously release cells into the presomitic mesoderm throughout somitogenesis is not understood. Using a genetic approach to study the MPCs, we show that a subset of MPCs are set aside very early in zebrafish development, and programmed to cell-autonomously enter the tail domain beginning with the 16th somite. Moreover, we show that the trunk is subdivided into two domains, and that entry into the anterior trunk, posterior trunk, and tail is regulated by interactions between the Nodal and bone morphogenetic protein (Bmp) pathways. Finally, we show that the tail MPCs are held in a state we previously called the Maturation Zone as they wait for the signal to begin entering somitogenesis.