Surface antigen differentiation during human myogenesis in culture

Abstract

The fusion of mononucleate myoblast cells into multinucleate myotubes (myogenesis) has often been studied as a model system of terminal cellular differentiation¹. Although cell-surface changes during myogenesis have attracted much attention and a variety of surface antigens including the nicotinic cholinergic receptor², acetylcholinesterase³ and muscle lectins^4,5 have been shown to be present on muscle cells, a detailed identification of markers specific to the various cell types has not been attempted. This is mainly because fibroblasts are a major contaminating cell type in primary muscle cultures and these cells have no known distinctive cell-surface antigen(s). For instance, surface fibronectin has been used to distinguish fibroblasts in the rat peripheral nervous system in vitro⁶ but has proved ineffective in the human muscle cell system⁷. In addition, Lesley and Lennon⁸ found that Thy-1 antigen was present on myoblasts but not myotubes of the rat L6 muscle cell line and primary cultures. However, Thy-1 antigen is also present on rpt fibroblasts^8,9. Thus, unequivocal identification of the major mononucleate ceil types in muscle cultures, fibroblasts and myoblasts has not been possible. We report here tlie use of two surface antigens, Thy-1 and a muscle-specific antigen recognized by a monoclonal antibody, to identify unambiguously the four major types of cells present in human muscle cultures and to propose a model of cell-surface differentiation during human myogenesis.