Membrane-cytoskeleton associations during myogenesis

Several monoclonal antibodies directed at the myoblast cell surface either inhibited or promoted the fusion of L8E63 rat skeletal muscle cells in culture, and this suggests that the fusion of skeletal myoblasts is regulated by distinct, cell surface components. Such perturbations of myoblast fusion by antibodies may reflect interactions between the cell surface and cytoskeleton in developing muscle. To examine this possibility, plasma membrane-cytoskeleton associations involving specific membrane proteins were studied in developing L8E63 cells on the basis of the following criteria: Triton-insolubility, co-localization and co-extraction with cytoskeletal proteins, and sensitivity to cytoskeleton-directed drugs. The cell surface dynamics of membrane proteins resulting from their crosslinking by antibodies were also studied in developing muscle. The results presented demonstrate that there are (i) developmental stage-specific associations between membrane proteins and the cytoskeleton and (ii) stage-specific cell surface dynamics during skeletal myogenesis. As a result of such cytoskeletal constraints on the topography and mobility of integral membrane proteins, the sarcolemma of developing muscle may become partitioned into specific functional membrane domains. Several inconsistencies with traditional expectations of membrane-cytoskeleton associations were found in these experiments, and the results further demonstrate that: (iii) neither Triton-insolubility nor co-localization alone predict all membrane-cytoskeleton associations: some associations between the membrane and cytoskeleton are unstable in non-ionic detergent; (iv) the native distribution of membrane proteins may not reflect their cytoskeletal associations; and (v) the topography of some membrane proteins with no apparent physical association with the cytoskeleton may nonetheless be greatly influenced by the cytoskeleton. I conclude that membrane-cytoskeleton associations in developing muscle are more abundant and dynamic than previously indicated and constitute a molecular basis for the vast membrane remodeling that is fundamental to the process of myogenesis.U of I OnlyETDs are only available to UIUC Users without author permissio