title: Differential regulation of synchronous versus asynchronous neurotransmitter release by the C2 domains of synaptotagmin 1.
abstract: Synaptic vesicle fusion at many synapses has been kinetically separated into two distinct Ca(2+)-dependent temporal components consisting of a rapid synchronous phase followed by a slower asynchronous component. Mutations in the synaptic vesicle Ca(2+) sensor Synaptotagmin 1 (Syt 1) reduce synchronous neurotransmission while enhancing the slower asynchronous phase of release. Syt 1 regulation of vesicle fusion requires interactions mediated by its tandem cytoplasmic C2 domains (C2A and C2B). Although Ca(2+) binding by Syt 1 is predicted to drive synchronous release, it is unknown if Ca(2+) interactions with either C2 domain is required for suppression of asynchronous release. To determine if Ca(2+) binding by Syt 1 regulates these two phases of release independently, we performed electrophysiological analysis of transgenically expressed Syt 1 mutated at Ca(2+) binding sites in C2A or C2B in the background of Drosophila Syt 1-null mutants. Transgenic animals expressing mutations that disrupt Ca(2+) binding to C2A fully restored the synchronous phase of neurotransmitter release, whereas the asynchronous component was not suppressed. In contrast, rescue with Ca(2+)-binding mutants in C2B displayed little rescue of the synchronous release component, but reduced asynchronous release. These results suggest that the tandem C2 domains of Syt 1 play independent roles in neurotransmission, as Ca(2+) binding to C2A suppresses asynchronous release, whereas Ca(2+) binding to C2B mediates synchronous fusion.
authors.affiliation: Picower Institute for Learning and Memory, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. motojiro.yoshihara@umassmed.edu
authors.forename: Motojiro
authors.initials: M
authors.lastname: Yoshihara
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Guan
authors.forename: J Troy
authors.initials: JT
authors.lastname: Littleton
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics / Q000502:physiology*; D005260:Female; D006982:Hypertonic Solutions / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D009154:Mutation; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism / Q000502:physiology; D050863:Synaptotagmin I / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D006982:Hypertonic Solutions; D018377:Neurotransmitter Agents; D050863:Synaptotagmin I; D002118:Calcium