Elucidation of aspects of murine skeletal muscle regeneration using local and whole body irradiation.

To investigate the role of proliferating local and emigrating circulatory leucocytes in skeletal muscle regeneration in mice, their bone marrow was ablated with whole body irradiation and compared with the effects of local irradiation. The results indicate that (1) the sealing of damaged myofibres is a function of local cells and is not dependent on the presence of infiltrating leucocytes; (2) the formation of sarcoplasmic projections at the ends of damaged myofibres is dependent on leucocyte infiltration; (3) nuclei in the sarcoplasmic projections are probably derived from fusion of muscle precursor cells; (4) most muscle precursor cells in vivo replicate at least once before fusion; and (5) both replication and fusion of muscle precursors can occur in the absence of infiltrating leucocytes. These results are discussed with respect to the interaction of various cell populations during regeneration of skeletal muscle, and are of clinical significance to pathological changes seen in many myopathies.