Myogenic cell replication in minced skeletal muscle isografts of Swiss and BALBc mice

The onset and pattern of muscle precursor replication in minced skeletal muscle isografts were examined autoradiographically in 22 BALBc and 23 Swiss mice. Tritiated thymidine was injected into mice at various times after grafting to label replicating muscle precursors and regenerated muscle isografts removed 14 days after grafting when labeled precursors had fused into myotubes. Analysis of labeled myotube nuclei in regenerated minced isografts showed a difference between the onset of DNA synthesis in muscle precursors of the two strains, although precursor proliferation peaked around day 5 and was greatly reduced by day 8 in both strains. The onset and duration of muscle precursor replication was similar to that seen in isografts of intact whole muscles: however, precursor proliferation was delayed and protracted compared with injured muscles. This autoradiographic model enables quantitative investigations of muscle precursor behavior in vivo, with clinical potential for improving muscle regeneration after severe injury, transplantation, and some myopathies.