Stem cells play a central role in development and maintenance of tissues and organs in the body of animals and humans. During growth or regeneration, skeletal muscle cells are unable to divide but replenish from a population of progenitor stem cells, which have the unique ability to divide, to produce copies of themselves as well as differentiating muscle cells. The team leader has previously identified and characterized a novel major progenitor stem cell population which gives rise to nearly all skeletal muscle cells, inluding the myogenic stem cell population of the adult, and identified key transcription regulators (Pax3 and Pax7) implicated in survival, specification and proliferation of these cells. Muscle differentiation is a coordinated process of tissue-specific gene expression and irreversible cell cycle exit. Failure or dysregulations of these processes either lead to apoptosis or cancer.