title: Synapsin regulates activity-dependent outgrowth of synaptic boutons at the Drosophila neuromuscular junction.
abstract: Patterned depolarization of Drosophila motor neurons can rapidly induce the outgrowth of new synaptic boutons at the larval neuromuscular junction (NMJ), providing a model system to investigate mechanisms underlying acute structural plasticity. Correlative light and electron microscopy analysis revealed that new boutons typically form near the edge of postsynaptic reticulums of presynaptic boutons. Unlike mature boutons, new varicosities have synaptic vesicles which are distributed uniformly throughout the bouton and undeveloped postsynaptic specializations. To characterize the presynaptic mechanisms mediating new synaptic growth induced by patterned activity, we investigated the formation of new boutons in NMJs lacking synapsin [Syn(-)], a synaptic protein important for vesicle clustering, neurodevelopment, and plasticity. We found that budding of new boutons at Syn(-) NMJs was significantly diminished, and that new boutons in Syn(-) preparations were smaller and had reduced synaptic vesicle density. Since synapsin is a target of protein kinase A (PKA), we assayed whether activity-dependent synaptic growth is regulated via a cAMP/PKA/synapsin pathway. We pretreated preparations with forskolin to raise cAMP levels and found this manipulation significantly enhanced activity-dependent synaptic growth in control but not Syn(-) preparations. To examine the trafficking of synapsin during synaptic growth, we generated transgenic animals expressing fluorescently tagged synapsin. Fluorescence recovery after photobleaching analysis revealed that patterned depolarization promoted synapsin movement between boutons. During new synaptic bouton formation, synapsin redistributed upon stimulation toward the sites of varicosity outgrowth. These findings support a model whereby synapsin accumulates at sites of synaptic growth and facilitates budding of new boutons via a cAMP/PKA-dependent pathway.
authors.affiliation: Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico 00960-6032, and.
authors.forename: Alexander
authors.initials: A
authors.lastname: Vasin
authors.affiliation: Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico 00960-6032, and.
authors.forename: Lidia
authors.initials: L
authors.lastname: Zueva
authors.affiliation: Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico 00960-6032, and.
authors.forename: Carol
authors.initials: C
authors.lastname: Torrez
authors.affiliation: The Picower Institute of Learning and Memory, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307.
authors.forename: Dina
authors.initials: D
authors.lastname: Volfson
authors.affiliation: The Picower Institute of Learning and Memory, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307.
authors.forename: J Troy
authors.initials: JT
authors.lastname: Littleton
authors.affiliation: Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico 00960-6032, and mb.ucdelcaribe@gmail.com.
authors.forename: Maria
authors.initials: M
authors.lastname: Bykhovskaia
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D030801:Animals, Genetically Modified; D016827:CD8 Antigens / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D051959:ELAV Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D017348:Microscopy, Electron, Scanning Transmission; D009469:Neuromuscular Junction / Q000166:cytology*; D038761:Photobleaching; D017729:Presynaptic Terminals / Q000502:physiology* / Q000648:ultrastructure; D016704:Synapsins / Q000235:genetics / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000276:Adjuvants, Immunologic; D016827:CD8 Antigens; D029721:Drosophila Proteins; D051959:ELAV Proteins; C498009:ELAV protein, Drosophila; C557617:GAL4 protein, Drosophila; D008164:Luminescent Proteins; D016704:Synapsins; D014157:Transcription Factors; D005576:Colforsin; D002118:Calcium
keywords: FRAP; active zone; electron microscopy; forskolin; synaptic vesicle; synaptotagmin
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