Ultrastructural localization of alpha-, beta- and gamma-sarcoglycan and their mutual relation, and their relation to dystrophin, beta-dystroglycan and beta-spectrin in normal skeletal myofiber

Ultrastructural localization of alpha-, beta- and gamma-sarcoglycan and the ir mutual relation, and their relation to dystrophin, beta-dystroglycan and beta-spectrin were investigated in normal skeletal myofibers. Single-immun ogold labeling electron microscopy showed that the signals of rabbit and sh eep polyclonal antibodies against the synthetic peptide of the cytoplasmic domain of alpha-, beta or gamma-sarcoglycan were present along the inside s urface of muscle plasma membrane and at the sarcoplasmic side of plasma mem brane invaginations and vesicular structures in subsarcolemmal areas. These localizations were similar to that of dystrophin, beta-dystroglycan and be ta-spectrin. Double-immunogold labeling disclosed the close association of alpha-, beta- and gamma-sarcoglycan each other and alpha-, beta-, gamma-sar coglycan with dystrophin or beta-dystroglycan, and this was confirmed by st atistical analysis. Monoclonal antibody against the extracellular domain of alpha-sarcoglycan was used with above-mentioned polyclonal anti-beta- and -gamma-sarcoglycan antibodies for triple-immunogold labeling, in which sign als of alpha-sarcoglycan localized at the outer surface of muscle plasmalem ma and those of beta- and gamma-sarcoglycans were present at the inside sur face of plasma membrane. The triple immunolabeling showed an occasional clo sely associated presence of the three signals for alpha-, beta- and gamma-s arcoglycans, and a more frequent association for two signals out of alpha-, beta- and gamma-sarcoglycans. This study demonstrated that alpha-, beta- a nd gamma-sarcoglycan are closely located to one another and to dystrophin a nd beta-dystroglycan at the muscle plasma membrane.