title: Functional Roles of Complexin 3 and Complexin 4 at Mouse Photoreceptor Ribbon Synapses.
abstract: Complexins (Cplxs) are SNARE complex regulators controlling the speed and Ca(2+) sensitivity of SNARE-mediated synaptic vesicle fusion. We have shown previously that photoreceptor ribbon synapses in mouse retina are equipped with Cplx3 and Cplx4 and that lack of both Cplxs perturbs photoreceptor ribbon synaptic function; however, Cplx3/4 function in photoreceptor synaptic transmission remained elusive. To investigate Cplx3/4 function in photoreceptor ribbon synapses, voltage-clamp recordings from postsynaptic horizontal cells were performed in horizontal slice preparations of Cplx3/4 wild-type (WT) and Cplx3/4 double knock-out (DKO) mice. We measured tonic activity in light and dark, current responses to changes in luminous intensity, and electrically evoked postsynaptic responses. Cplx3/4 decreased the frequency of tonic events and shifted their amplitude distribution to smaller values. Light responses were sustained in the presence of Cplx3/4, but transient in their absence. Finally, Cplx3/4 increased synaptic vesicle release evoked by electrical stimulation. Using electron microscopy, we quantified the number of synaptic vesicles at presynaptic ribbons after light or dark adaptation. In Cplx3/4 WT photoreceptors, the number of synaptic vesicles associated with the ribbon base close to the release site was significantly lower in light than in dark. This is in contrast to Cplx3/4 DKO photoreceptors, in which the number of ribbon-associated synaptic vesicles remained unchanged regardless of the adaptational state. Our results indicate a suppressing and a facilitating action of Cplx3/4 on Ca(2+)-dependent tonic and evoked neurotransmitter release, respectively, and a regulatory role in the adaptation-dependent availability of synaptic vesicles for release at photoreceptor ribbon synapses.
  
  
  
  Synaptic vesicle fusion at active zones of chemical synapses is executed by SNARE complexes. Complexins (Cplxs) are SNARE complex regulators and photoreceptor ribbon synapses are equipped with Cplx3 and Cplx4. The absence of both Cplxs perturbs ribbon synaptic function. Because we lack information on Cplx function in photoreceptor synaptic transmission, we investigated Cplx function using voltage-clamp recordings from postsynaptic horizontal cells of Cplx3/4 wild-type and Cplx3/4 double knock-out mice and quantified synaptic vesicle number at the ribbon after light and dark adaptation using electron microscopy. The findings reveal a suppressing action of Cplx3/4 on tonic neurotransmitter release, a facilitating action on evoked release, and a regulatory role of Cplx3/4 in the adaptation-dependent availability of synaptic vesicles at mouse photoreceptor ribbon synapses.
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and.
authors.forename: Norbert
authors.identifier: 0000-0002-9348-0546
authors.initials: N
authors.lastname: Babai
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and.
authors.forename: Anna
authors.initials: A
authors.lastname: Sendelbeck
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and.
authors.forename: Hanna
authors.initials: H
authors.lastname: Regus-Leidig
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and.
authors.forename: Michaela
authors.identifier: 0000-0001-7778-6708
authors.initials: M
authors.lastname: Fuchs
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Mertins
authors.affiliation: Department of Molecular Neurobiology and Center for the Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Reim
authors.affiliation: Department of Molecular Neurobiology and Center for the Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
authors.forename: Nils
authors.identifier: 0000-0003-0938-8534
authors.initials: N
authors.lastname: Brose
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and johann.helmut.brandstaetter@fau.de andreas.feigenspan@fau.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Feigenspan
authors.affiliation: Department of Biology, Animal Physiology, Friedrich Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany, and johann.helmut.brandstaetter@fau.de andreas.feigenspan@fau.de.
authors.forename: Johann Helmut
authors.identifier: 0000-0002-6468-5585
authors.initials: JH
authors.lastname: Brandstätter
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology* / Q000648:ultrastructure; D012160:Retina / Q000166:cytology*; D050600:SNARE Proteins / Q000378:metabolism; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000235:genetics*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; C529624:Cplx3 protein, mouse; C543115:Cplx4 protein, mouse; D005136:Eye Proteins; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; C498771:Rac3 protein, mouse; D020744:rac GTP-Binding Proteins; D002118:Calcium