title: Differential regulation of evoked and spontaneous neurotransmitter release by C-terminal modifications of complexin.
abstract: Complexins are small α-helical proteins that modulate neurotransmitter release by binding to SNARE complexes during synaptic vesicle exocytosis. They have been found to function as fusion clamps to inhibit spontaneous synaptic vesicle fusion in the absence of Ca(2+), while also promoting evoked neurotransmitter release following an action potential. Complexins consist of an N-terminal domain and an accessory α-helix that regulates the activating and inhibitory properties of the protein, respectively, and a central α-helix that binds the SNARE complex and is essential for both functions. In addition, complexins contain a largely unstructured C-terminal domain whose role in synaptic vesicle cycling is poorly defined. Here, we demonstrate that the C-terminus of Drosophila complexin (DmCpx) regulates localization to synapses and that alternative splicing of the C-terminus can differentially regulate spontaneous and evoked neurotransmitter release. Characterization of the single DmCpx gene by mRNA analysis revealed expression of two alternatively expressed isoforms, DmCpx7A and DmCpx7B, which encode proteins with different C-termini that contain or lack a membrane tethering prenylation domain. The predominant isoform, DmCpx7A, is further modified by RNA editing within this C-terminal region. Functional analysis of the splice isoforms showed that both are similarly localized to synaptic boutons at larval neuromuscular junctions, but have differential effects on the regulation of evoked and spontaneous fusion. These data indicate that the C-terminus of Drosophila complexin regulates both spontaneous and evoked release through separate mechanisms and that alternative splicing generates isoforms with distinct effects on the two major modes of synaptic vesicle fusion at synapses.
authors.affiliation: Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
authors.forename: Lauren K
authors.initials: LK
authors.lastname: Buhl
authors.forename: Ramon A
authors.initials: RA
authors.lastname: Jorquera
authors.forename: Yulia
authors.initials: Y
authors.lastname: Akbergenova
authors.forename: Sarah
authors.initials: S
authors.lastname: Huntwork-Rodriguez
authors.forename: Dina
authors.initials: D
authors.lastname: Volfson
authors.forename: J Troy
authors.initials: JT
authors.lastname: Littleton
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005089:Exocytosis; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050600:SNARE Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D020033:Protein Isoforms; D050600:SNARE Proteins