Role of Cell-Surface Glycoconjugates in Myogenesis.

Abstract

In the differentiation of skeletal myoblasts, the cells, after aligning themselves in arrays, fuse to form myotubes. Although it has been suggested that high mannose type of glycoproteins may be invloved in differentiation, mutant myoblasts lacking high mannose type of chains are capable of myotube formation. There is evidence that some new glycoproteins are produced by myoblasts which participate in fusion. Before differentiation the cells bind to the extracellular matrix through integrin receptors. Cell-cell adhesion of myoblasts occurs through two types of mechanisms, one calcuim-dependent and another calcium-independent. The former type of interaction is homophilic and brought about by membranelocalized N- and M-cadherins. The calcium-independent mechanism involves participation of neural cell adhesion molecules (NCAMs), especially the forms linked to plasma membrane through glycosyl-phosphatidylinositol residues. The NCAMs are sialoglycoproteins which are capable of exsisting as isoforms. Transfection of phospholipid-linked form of human NCAM cDNA in myoblasts leads precocious differentiation.