ULTRASTRUCTURAL-LOCALIZATION OF THE C-TERMINUS OF THE 43-KD DYSTROPHIN-ASSOCIATED GLYCOPROTEIN AND ITS RELATION TO DYSTROPHIN IN NORMAL MURINE SKELETAL MYOFIBER

We used single and double immunogold labeling electron microscopy to i nvestigate ultrastructural localization of the C terminus of the 43-kd dystrophin-associated glycoprotein (43-DAG) and its relationship to d ystrophin in normal murine skeletal myofibers. Single immunolabeling l ocalized the antibody against the C terminus of 43-DAG to the inside s urface of the muscle plasma membrane and the sarcoplasmic sine of plas ma membrane invaginations. Double immunolabeling co-localized antibodi es against dystrophin and the C terminus of 43-DAG to the same site no ted in the single immunolabeling localization of 43-DAG, In particular , dystrophin and the C-terminal 43-DAG antibody signals were often obs erved as doublets separated by less than 30 nm. We compared these resu lts with those obtained from double immunogold labeling with anti-dyst rophin and anti-beta-spectrin, as well as anti-C-terminal 43-DAG and a nti-beta-spectrin antibodies. The antibodies against dystrophin and be ta-spectrin, or beta-spectrin and 43-DAG, also co-localized to similar sites in skeletal muscle fibers. Signals of doublet formations were n oted but their frequency was significantly lower than the doublet freq uency of anti-dystrophin and anti-43-DAG antibodies. The results suppo rt the presence of dystrophin and 43-DAG linkage at the inside surface of the murine skeletal muscle plasma membrane.