Myogenic progenitor cells and skeletal myogenesis in vertebrates.

Continuing research on the onset of skeletal myogenesis in the somite is providing new insights into the behaviour of early myogenic progenitor cells and how signalling molecules affect cell fate decisions, in addition to subsequent muscle growth. Genetic manipulations have revealed new regulatory aspects, including the role of Six transcription factors and the CXCR4 cytokine receptor during embryonic myogenesis. An important recent development is the identification of a novel population of somite-derived cells that make a major contribution to muscle growth. These cells, which are characterised by the expression of Pax3 and Pax7, also give rise to the satellite cells of postnatal muscle. The relationship between Pax and Myogenic regulatory factors has been explored. Furthermore, Pax7 is now shown to be required for the maintenance of satellite cells. New approaches that permit the grafting of purified satellite cells demonstrate their capacity for efficient muscle repair and for self-renewal. Regeneration in amphibians is now also shown to involve Pax-positive progenitor cells.