Bone Abstracts

The formation of skeletal muscle depends on myogenic regulatory factors of the MyoD family that are essential for entry into the myogenic programme and subsequent differentiation of muscle fibres. More recently attention has focussed on upstream regulators of muscle progenitor cells, prior to activation of the myogenic determination genes Myf5 and MyoD. In this context, Pax3 and Pax7 play an important role. In the embryo, Pax3 marks muscle stem cells that give rise to trunk and limb muscles. Pax7 is subsequently co-expressed with Pax3 in this cell population that fuels muscle growth during development. In adult muscle, Pax7/3 positive cells, now present as quiescent satellite cells on muscle fibres, are activated on injury and ensure regeneration of the tissue. The behaviour of skeletal muscle stem cells will be discussed in the context of developmental and regenerative myogenesis.