| Annotated protein: | 43 kDa receptor-associated protein of the synapse (RAPsyn) (43 kDa postsynaptic protein) (Acetylcholine receptor-associated 43 kDa protein). Gene symbol: RAPSN. Taxonomy: Mus musculus (Mouse). Uniprot ID: P12672 |
| antibody wiki: | |
| SynGO gene info: | SynGO data @ RAPSN |
| Ontology domain: | Biological Process |
| SynGO term: | neurotransmitter receptor localization to postsynaptic specialization membrane (GO:0099645) |
| Synapse type(s): | Neuro-muscular junction |
| Annotated paper: | Li L, et al. "Enzymatic Activity of the Scaffold Protein Rapsyn for Synapse Formation" Neuron. 2016 Dec 7;92(5):1007-1019 PMID:27839998 |
| Figure(s): | Fig.2, S2, 3, 7 |
| Annotation description: | Rapsyn is a protein of the NMJ postsynaptic density. It is known to bind AChRs and actin. Rapsyn is needed for the clustering of AChRs at the NMJ. When expressed in heterologous cells Rapsyn by itself is able to aggregate and cluster nAChRs. Because of the nAChR clustering properties and the interaction with the actin cytoskeleton Rapsyn is generally considered a postsynaptic scaffold ('structural constituent of postsynaptic specialization') that localizes NTRs to the postsynapse. This paper shows that the nACHR clustering role of Rapsyn depends on its enzymatic modification of this receptor. Fig.2: "Inability of C366A Rapsyn to Rescue NMJ Deficits in Rapsyn Null Mutant Mice" - "Expression of WT rapsyn in null mice prevented null mice from dying and the NMJs were observed in R-/-;HSA-RWT mice (Figures 2A and 2B), demonstrating that muscle expression of WT rapsyn is able to rescue NMJ deficits of rapsyn null mice. In contrast, R-/-;HSA-RC366A mice died soon after birth with cyanosis, a sign of inability to breathe, suggesting that the C366A mutant is unable to rescue." Fig.S2+3: - "The C366A mutation seemed to have little effect on rapsyn protein stability in HEK293T cells (Figure S2A) and on its binding to actin (Figure S2B)." - "As shown in Figures S2D and S2E, C366A associated with AChR subunits as WT control. Next, we determined whether the enzyme activity of rapsyn regulates AChR cluster formation. Ideally, agrin-induced AChR clusters in muscle cells may serve as a readout; however, increasing rapsyn levels in cultured muscle cells are known to inhibit agrin-induced clusters (Han et al., 1999; Yoshihara and Hall, 1993)." - "Rapsyn overexpression causes AChR to form aggregates in non-muscle cells (Froehner et al., 1990; Gillespie et al., 1996; Phillips et al., 1991), and we investigated whether this event requires the enzymatic activity of rapsyn. As shown in Figure 3A, α, β, γ, and δ AChR subunits, when expressed in combination, did not form aggregates in control HEK293T cells that were transfected with GFP. However, co-expression of rapsyn-GFP or rapsyn alone led to the formation of AChR aggregates (Figures 3A, 3B, and S3A)." Fig.7: "Aberrant NMJ Formation in Rapsyn C366A Mutant Mice" - "To characterize the NMJ, we stained muscles of WT and RCA/CA mice whole mount for AChR and nerve terminals, together with rapsyn null (R-/-) mice as control. As shown in Figure 7A, RCA/CA mice did not form AChR clusters in diaphragm muscles (Figures 7A and 7B) and in other muscles including tibialis anterior muscles (Figure S6H), resembling the phenotypes of rapsyn null mice (Gautam et al., 1995). On the other hand, motor nerve terminals of diaphragm muscles in both RCA/CA and rapsyn null mice failed to stop in the central region of muscle fibers and branched extensively (Figures 7A and 7B). Consequently, the length of secondary branches was increased in RCA/CA and rapsyn null mice, compared with WT mice (Figures 7A, 7B, and 7D). At the level of electron microscopy, junctional folds could be frequently identified in WT muscles. Opposed to junctional folds were axon terminals filled with homogeneous synaptic vesicles. Active zones were occasionally visible on the presynaptic membrane where vesicles were clustered (Figure S6I). In muscles of RCA/CA mice, axon terminals were identifiable with synaptic vesicles." |
| Evidence tracking, Biological System: | Intact tissue Non-neuronal tissue |
| Evidence tracking, Protein Targeting: | Genetic transformation (eg; knockout, knockin, mutations) Over-expression Antibody (detection) |
| Evidence tracking, Experiment Assay: | Confocal IP + WB/MSMS |
| Annotator(s): | Pim van Nierop (ORCID:0000-0003-0593-3443) Guus Smit (ORCID:0000-0002-2286-1587) Matthijs Verhage (ORCID:0000-0002-2514-0216) |
| Lab: | Department of Functional Genomics, Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands |
| SynGO annotation ID: | 3027 |
| Dataset release (version): | 20231201 |
| View annotation as GO-CAM model: |  |