[Pathophysiology in muscle fiber necrosis and regeneration with a particular reference to regenerating process]

It is well known that muscle fiber is capable of regeneration after myonecrosis even in a case of muscular dystrophies. We first examined how and when the regulatory genes for myogenesis, MyoD and myogenin were expressed in experimentally induced myonecrosis. MyoD, a responsible gene for myoblast proliferation began to express at 18 hours and reached to the maximum level 48 hours after necrosis. Myogenin known to play a role for myotube formation was most extensively expressed 72 hours after myonecrosis when the newly formed myotubes were recognizable, confirming that both genes were necessary for regenerating process. The MyoD and myogenin were also expressed in regenerating fibers in muscular dystrophies including dy mouse with progressive muscle weakness and mdx mouse with no apparent muscle symptom. The genes were more extensively expressed in mdx mouse, than dy mouse simply reflecting their respective regenerating activity.