A myosin isoform repressed in hypertrophied ALD muscle of the chicken reappears during regeneration following cold injury

A library of monoclonal antibodies specific for myosin heavy chain (HC) was used to study myosin expression in regenerating fibers. The response to cold injury of slow skeletal ALD muscle previously induced to eliminate SM1 myosin by weight overload was compared to that of its contralateral control. Native gel electrophoresis combined with immunoblotting demonstrated that slow SM1 myosin HC eliminated from hypertrophic muscle reappeared both at the site of active regeneration and unexpectedly, also distal to the site of injury. The regeneration response of hypertrophied muscles was similar to that of the controls. In addition to SM1 myosin HC, ventricular-like and embryonic/fast isoforms were also expressed in both muscles during the early stages of regeneration and disappeared as the muscle fibers matured. These observations demonstrate that regenerating slow muscle fibers reexpress myosins' characteristic of developing muscle irrespective of the myosin phenotype prior to injury. The reappearance of repressed myosin HC in the hypertrophied ALD muscle is consistent with the presence of newly differentiated myonuclei.