Differences among myosins synthesized in non-myogenic cells, presumptive myoblasts, and myoblasts.

Myosins synthesized in non-myogenic cells and replicating presumptive myoblasts differ from those synthesized in postmitotic mononucleated myoblasts and myotubes. Myoblasts and myotubes synthesize the definitive light chains, MLC1 and MLC2. These light chains display different molecular weights in sodium dodecyl sulfate-polyacrylamide gels from the fibroblast light chains FLC1 and FLC2 synthesized in non-myogenic cells and presumptive myoblasts. There are immunological differences between the myosin heavy chains synthesized in myoblasts and myotubes and those synthesized in non-myogenic cells and presumptive myoblasts. Fluorescein-labeled antibodies against skeletal light meromyosin are bound only along the lateral edges of emerging and definitive A-bands. This antibody to light meromyosin is not bound to the outside of, or the microfilaments subtending, the plasma membrane in non-myogenic cells or in myoblasts or in myotubes. These findings suggest that: (1) non-myogenic cells and replicating presumptive myoblasts synthesize similar myosin heavy and light chains; (2) replicating presumptive myoblasts synthesize a different set of myosins from those synthesized by their postmitotic daughters, the myoblasts; (3) the myosins associated with the plasma membranes of non-myogenic and myogenic cells are products of structural genes distinct from those coding for the myosins for skeletal myofibrils.