Regeneration of adult newt skeletal muscle tissue in vitro.

Explants and cells of forelimb muscle from adult Notophthalmus viridescens were cultured for periods up to 160 days in MEM-based medium supplemented with serum, hormones, and antibiotics. Explants which were not minced prior to culture contained muscle fibres with healthy myonuclei and no evidence of dedifferentiation after four weeks. Explants which were minced prior to culture contained degenerated muscle fibres after 1 day and no evidence of dedifferentiation after four weeks. Mononucleated cells from both minced and non-minced explants proliferated. Cell proliferation and myotube formation was greater in the minced muscle cultures. Proliferation and fusion of myoblasts and subsequent formation of myofibrils were observed on the plate in primary cultures. Secondarily transferred cells proliferated and fused into myotubes. Although adult newt muscle does not contain satellite cells, myogenesis in this amphibian followed the same course as all other vertebrate skeletal muscle: proliferation of mononucleated myogenic cells, fusion of the myoblasts to form syncytia, and eventual accumulation of myofibrils. The ultimate source of the myogenic cells was not identified; however, the absence of dedifferentiation of the mature fibres and the occurrence of myogenesis in cultures of minced muscle explants demonstrated that the regenerated muscle developed from a population of mononucleated cells whose origin did not depend upon dedifferentiation of intact fibres.