Neuromuscular synapse integrity requires linkage of acetylcholine receptors to postsynaptic intermediate filament networks via rapsyn-plectin 1f complexes.
Bottom Line: Live imaging of acetylcholine receptors (AChRs) in cultured myotubes differentiated ex vivo from immortalized plectin-deficient myoblasts revealed them to be highly mobile and unable to coalesce into stable clusters, in contrast to wild-type cells.In their phenotypic behavior, mutant mice closely mimicked EBS-MD-MyS patients, including impaired body balance, severe muscle weakness, and reduced life span.Our study demonstrates that linkage to desmin IF networks via plectin is crucial for formation and maintenance of AChR clusters, postsynaptic NMJ organization, and body locomotion.
Affiliation: Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria.Show MeSH
Related in: MedlinePlus
Mentions: To visualize the dynamic interplay of AChR clusters and IFs, we performed live imaging of desmin–green fluorescent protein (GFP)–transfected Plec+/+ and Plec−/− myotubes that after withdrawal of agrin were additionally labeled with Rhodamine Red–streptavidin-biotin-α-BTX. Monitoring Plec+/+ cells for up to 2 h in the absence of agrin, we observed compact and relatively immobile AChR clusters enclosed in a lattice of desmin IFs (Figure 3A and Supplemental Video S1). In contrast, in Plec−/− myotubes, collapsed desmin IF networks were visualized as aggregates that were distant from receptor clusters without showing any overlap. Of interest, already as early as 6 min after initiating the imaging period, fragmentation and a drifting away from IF-disconnected larger clusters could be observed in this case (Figure 3B and Supplemental Video S2). Moreover, large clusters as a whole were changing their position within the plane of the sarcolemma (Figure 3B and Supplemental Video S2). Finally, transient and apparently unstable interactions between microclusters were detected, suggesting that these structures were unable to fuse into more stable larger clusters (Figure 3B and Supplemental Video S2). When agrin-induced AChR cluster formation was monitored by live imaging of transfected GFP-AChR-ε-subunit instead of α-BTX labeling, similar results were obtained (Supplemental Videos S5 and S6).
Affiliation: Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria.