title: An Endocytic Scaffolding Protein together with Synapsin Regulates Synaptic Vesicle Clustering in the Drosophila Neuromuscular Junction.
abstract: Many endocytic proteins accumulate in the reserve pool of synaptic vesicles (SVs) in synapses and relocalize to the endocytic periactive zone during neurotransmitter release. Currently little is known about their functions outside the periactive zone. Here we show that in the Drosophila neuromuscular junction (NMJ), the endocytic scaffolding protein Dap160 colocalizes during the SV cycle and forms a functional complex with the SV-associated phosphoprotein synapsin, previously implicated in SV clustering. This direct interaction is strongly enhanced under phosphorylation-promoting conditions and is essential for proper localization of synapsin at NMJs. In a dap160 rescue mutant lacking the interaction between Dap160 and synapsin, perturbed reclustering of SVs during synaptic activity is observed. Our data indicate that in addition to the function in endocytosis, Dap160 is a component of a network of protein-protein interactions that serves for clustering of SVs in conjunction with synapsin. During the SV cycle, Dap160 interacts with synapsin dispersed from SVs and helps direct synapsin back to vesicles. The proteins function in synergy to achieve efficient clustering of SVs in the reserve pool.
  
  
  CONCLUSIONS
  We provide the first evidence for the function of the SH3 domain interaction in synaptic vesicle (SV) organization at the synaptic active zone. Using Drosophila neuromuscular junction as a model synapse, we describe the molecular mechanism that enables the protein implicated in SV clustering, synapsin, to return to the pool of vesicles during neurotransmitter release. We also identify the endocytic scaffolding complex that includes Dap160 as a regulator of the events linking exocytosis and endocytosis in synapses.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Åsa M E
authors.identifier: http://orcid.org/0000-0003-0064-7536
authors.initials: ÅM
authors.lastname: Winther
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Olga
authors.initials: O
authors.lastname: Vorontsova
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Rees
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Näreoja
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Elena
authors.initials: E
authors.lastname: Sopova
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Wei
authors.initials: W
authors.lastname: Jiao
authors.affiliation: Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden oleg.shupliakov@ki.se.
authors.forename: Oleg
authors.identifier: http://orcid.org/0000-0001-5352-6848
authors.initials: O
authors.lastname: Shupliakov
mesh_terms: D000818:Animals; D016000:Cluster Analysis; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology; D005260:Female; D008297:Male; D009469:Neuromuscular Junction / Q000378:metabolism* / Q000648:ultrastructure; D016704:Synapsins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: C113692:Dap160 protein, Drosophila; D029721:Drosophila Proteins; D016704:Synapsins; D033921:Vesicular Transport Proteins
keywords: Drosophila neuromuscular junction; scaffolding proteins; synapse; synapsin; synaptic vesicles; vesicle clustering