Characterization of a plasma membrane glycoprotein common to myoblasts, skeletal muscle satellite cells, and glia

A plasma membrane glycoprotein common to embryonic chick myoblasts and adult chicken skeletal muscle satellite cells is the antigen recognized by monoclonal antibody C3 1 . Although traces of the same antigen are present on some muscle-derived fibroblasts, the density of antigenic sites on myoblasts and satellite cells is so high that these cell types can be identified in tissues by immunocytochemical techniques. The antigen is exposed on the surfaces of myogenic cells growing in tissue culture and can be solubilized with detergent. This and other criteria establish that the antigen is a plasma membrane protein. The antigen, purified by affinity techniques, consists of a single type of polypeptide chain which migrates as a relatively broad band of apparent molecular weight 38,000 Da in SDS-polyacrylamide gel electrophoresis. It has a very small sedimentation constant, suggesting that the solubilized form is either monomeric or dimeric. The concentration of antigenic sites increases during myogenesis in vitro; but during maturation the antigenic sites are lost from muscle fibers. Electron microscopic autoradiographic study of adult muscle labeled with iodinated monoclonal antibody demonstrated unequivocally that the antigenic sites in adult muscle are concentrated in the satellite cells. Although selective for myoblasts, immature myotubes and satellite cells in the myogenic lineage, the monoclonal antibody also binds at rather high levels to peripheral Schwann cells and teloglia, to some nonneuronal cells in cultures derived from embryonic spinal cord, to some glial elements of adult chicken brain, and to several cell types in the early embryo.