Before hoping to discover the genetic primary defects involved in the etiology of disease of human muscle development (for example, the muscular dystrophies), an understanding of the biochemistry of the early stages of muscle development is essential. The cultivation of muscle cells in culture is a useful model for these studies. Myogenesis in vitro, in which myoblasts undergo cell contact and membrane fusion to form multinucleated, contractile myotubules, is a striking morphological event, and is a suitable model for studies of isoform transformations occurring during the early stages of fetal muscle development. Plasma membrane glycosphingolipids (both neutral glycolipids and gangliosides) impart functional specificity to the cell surface by being involved in cell-cell recognition events, receptor and antigenic functions and the promotion of cellular differentiation. Surprisingly, very few studies have been reported which address the changes and possible roles of these classes of complex carbohydrates during myoblast differentiation. The long-range objectives of this project are to understand, at both the cellular and molecular levels, structural and functional isoform changes occurring during muscle cell differentiation in vitro, and whether specific alternations in membrane glycolipids accompany myogenic differentiation. Preliminary data indicate significant increased biosynthesis of certain glycolipids during avain myoblast fusion. Whether these myogenic stage-specific alterations are important and could be extrapolated to the development of muscle tissue in other species (including man) can best be determined by comparison of several different in vitro myogenic models. This will be examined in a series of related experiments, with the following specific aims: 1) Establish in culture several different muscle cell types (especially new continuous myogenic models) for comparative in vitro studies of myogenesis; 2) Characterize the myogenic process in vitro, of these different muscle cell types, by morphometric and biochemical analysis; 3) Examine alterations in membrane glycosphingolipid biosynthesis during myogenesis in vitro by supplying radioactive monosaccharide precursors, cell surface labeling procedures, and quantitation of neutral glycolipids, gangliosides and glycoproteins by biochemical assay; 4) Examine alterations in relevant glycosyltransferases and glycohydrolases.
