COLOCALIZATION OF DYSTROPHIN AND BETA-DYSTROGLYCAN DEMONSTRATED IN ENFACE VIEW BY DOUBLE IMMUNOGOLD LABELING OF FREEZE-FRACTURED SKELETAL-MUSCLE

An absence of dystrophin causes Duchenne muscular dystrophy, but the p recise mechanism underlying necrosis of the muscle cells is still uncl ear. Dystrophin and beta-dystroglycan are components of a complex of a t least nine proteins, the dystrophin-glycoprotein complex (DGC), that links the membrane cytoskeleton to extracellular elements in skeletal and cardiac muscle. Biochemical studies indicate that dystrophin is b ound to other components of the DGC via beta-dystroglycan, which sugge sts that the distribution of these two proteins should be almost ident ical. In this study, therefore, we examined the spatial relationship b etween dystrophin and beta-dystroglycan with a range of different imag ing techniques to investigate the extent of the predicted co-localizat ion. We used (a) double immunogold fracture-label, a freeze-fracture c ytochemical technique that allows high-resolution face-on views of lab eled membrane components in thin sections and in platinum-carbon repli cas, (b) double immunogold labeling of cryosections and (c) confocal m icroscopy. Both dystrophin and beta-dystroglycan were found over the e ntire fiber surface and, when labeled singly, the nearest neighbor spa cing of labeling sites for the two proteins was indistinguishable. Wit h double labeling, very close co-localization could be demonstrated. T he results support the conclusion that dystrophin and beta-dystroglyca n directly interact at the muscle plasma membrane.