The localization of skeletal light meromyosin in cells of myogenic cultures.

Fluorescent antibodies against skeletal light meromyosin were used to study the localization of this muscle-specific antigen in myotubes, myoblasts, presumptive myoblasts and fibroblasts found in six-day myogenic cultures. The labelled antibody bound only to the lateral edges of the A-bands in myofibrils. The antibody did not bind to antigens in the nucleus, cytoplasm or in the microfilaments beneath the plasmalemma in any of the cell types examined. Similarly, the external face of the cell surface of unfixed, living myotubes and mononucleated cells did not bind the antibody. Immunodiffusion tests confirm these results: high salt extracts of myotube-containing cultures reacted against anti-skeletal light meromyosin, whereas extracts of fibroblasts and presumptive myoblast cultures failed to precipitate the antibody. It is proposed that if myosin is present in the plasmalemma of these cells, as is suggested bhe myofibrils of definitive muscle.