Skeletal muscle formation in vertebrates.

Research in the past year has added to our understanding of the signalling systems that specify myogenic identity in the embryo and of the regulation and roles of MyoD family members. New insights into the movement of muscle precursor cells include the demonstration that Lbx1 is essential for their migration from the somite to some but not all sites of muscle formation elsewhere. Later in development, ras as well as calcineurin signalling is now implicated in the definition of slow versus fast fibre types. The myogenic identity of precursor cells in the adult depends on Pax7, the orthologue of Pax3 which is required for early myogenesis; this finding is of major importance for muscle regeneration and the active field of stem cell research.