Summary

protein rapsyn is re-quired for the clustering of nicotinic acetylcholine re-ceptors (AChRs) at the developing neuromuscular junction, but the functions of other postsynaptic pro-teins colocalized with the AChR are less clear. Here we use a fibroblast expression system to investigate the role of the dystrophin-glycoprotein complex (DGC) in AChR clustering. The agrin-binding component of the DGC, dystroglycan, is found evenly distributed across the cell surface when expressed in fibroblasts. However, dystroglycan colocalizes with AChR-rapsyn clusters when these proteins are coexpressed. Fur-thermore, dystroglycan colocalizes with rapsyn clus-ters even in the absence of AChR, indicating that rapsyn can cluster dystroglycan and AChR indepen-dently. lmmunofluorescence staining using a poly-clonal antibody to utrophin reveals a lack of staining of clusters, suggesting that the immunoreactive species, like the AChR, does not mediate the observed rapsyn-dystroglycan interaction. Rapsyn may therefore be a molecular link connecting the AChR to the DGC. At the neuromuscular synapse, rapsyn-mediated linkage of the AChR to the cytoskeleton-anchored DGC may underlie AChR cluster stabilization