Developmental expression of sarcoglycan gene products in cultured myocytes

The sarcoglycan complex consists of four membrane-spanning proteins and was shown to be exclusively distributed in striated muscles. In this study, we analyzed the pattern of expression of the mRNAs and proteins of the sarcoglycan subunits during cell differentiation in a culture of myocytes. All four sarcoglycan mRNAs were detectable in proliferating cells, and expression of the alpha- and gamma-subunits was up-regulated by 20- and 50-fold following muscle cell fusion. However, sarcoglycan proteins were scarcely detectable in proliferating cells and were first detected 2 days after the induction to be differentiated. The accumulation of the sarcoglycan protein subunits was accompanied by cell differentiation. The discrepancy between the expression of the mRNAs and proteins of the sarcoglycan subunits in proliferating cells may be ascribed to rapid degradation of the protein.