The development of migrating muscle precursor cells.

A major subclass of hypaxial muscle groups is derived from long-range migrating precursor cells that delaminate from the dermomyotome. Migrating precursors are generated on particular axial levels only, i.e. occipitally, cervically, and on the levels of the fore and hind limbs. They express the homeobox gene Lbx1, which provides a useful marker for their visualization. In the mouse, migrating precursor cells give rise to muscles of the extremities, the hypoglossal chord, and the diaphragm. We discuss here the development of this migrating lineage, which critically depends on the correct specification of the precursors in the dermomyotome, their delamination and correct migration. Finally, proliferation at the targets is essential to ensure a correct size of the precursor pool and of the muscle that derives thereof.