Cell death in myoblasts and muscles.

One of the hallmarks of development is that many more cells are produced than are ultimately needed for organogenesis. In the case of striated skeletal muscle, large numbers of myoblasts are generated in the somites and then migrate to take up residence in the limbs and the trunk. A subset of these cells fuses to form multinucleated skeletal muscle fibers, while a second group, known as satellite cells, exits the cell cycle and persists as a pool of lineage-restricted stem cells that can repair damaged muscle. The remaining cells initiate apoptosis and are rapidly lost. Primary myoblasts and established satellite cell lines are powerful tools for dissecting the regulatory events that mediate differentiative decisions and have proven to be important models. As well, muscle diseases represent debilitating and often fatal disorders. This chapter provides a general background for muscle development and then details a variety of assays for monitoring the differentiation and the death of muscle. While some of these methods are specialized to address the phenotypic properties of skeletal muscle, others can be employed with a wide variety of cell types.