Establishing myogenic identity during somitogenesis.

Over the past year, interest has focused on identifying signalling molecules--including Wnts, Sonic hedgehog, BMP-4, and noggin--that divert somitic mesodermal cells into the muscle lineage, either by induction or derepression. New mouse mutants have also provided insights into somite formation and differentiation, as well as pointing to novel differences between head, trunk, and limb myogenic programmes. In addition, recent genetic, embryological, and molecular studies have shed new light on somite formation and the establishment of muscle progenitor cells.