Co-localization of Dystrophin and β-Dystroglycan Demonstrated in En Face View by Double Immunogold Labeling of Freeze-fractured Skeletal Muscle

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Abstract
SUMMARY An absence of dystrophin causes Duchenne muscular dystrophy, but the precise mechanism underlying necrosis of the muscle cells is still unclear. Dystrophin and β-dystroglycan are components of a complex of at 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 bound to other components of the DGC via β-dystroglycan, which suggests that the distribution of these two proteins should be almost identical. In this study, therefore, we examined the spatial relationship between dystrophin and β-dystroglycan with a range of different imaging techniques to investigate the extent of the predicted co-localization. We used (a) double immunogold fracture-label, a freeze-fracture cytochemical technique that allows high-resolution face-on views of labeled membrane components in thin sections and in platinum-carbon replicas, (b) double immunogold labeling of cryosections and (c) confocal microscopy. Both dystrophin and β-dystroglycan were found over the entire fiber surface and, when labeled singly, the nearest neighbor spacing of labeling sites for the two proteins was indistinguishable. With double labeling, very close co-localization could be demonstrated. The results support the conclusion that dystrophin and β-dystroglycan directly interact at the muscle plasma membrane.