1
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Nair AG, Bollmohr N, Schökle L, Keim J, Melero JMM, Müller M. Presynaptic quantal size enhancement counteracts post-tetanic release depression. J Physiol 2024. [PMID: 39183664 DOI: 10.1113/jp286176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Accepted: 07/30/2024] [Indexed: 08/27/2024] Open
Abstract
Repetitive synaptic stimulation can induce different forms of synaptic plasticity but may also limit the robustness of synaptic transmission by exhausting key resources. Little is known about how synaptic transmission is stabilized after high-frequency stimulation. In the present study, we observed that tetanic stimulation of the Drosophila neuromuscular junction (NMJ) decreases quantal content, release-ready vesicle pool size and synaptic vesicle density for minutes after stimulation. This was accompanied by a pronounced increase in quantal size. Interestingly, action potential-evoked synaptic transmission remained largely unchanged. EPSC amplitude fluctuation analysis confirmed the post-tetanic increase in quantal size and the decrease in quantal content, suggesting that the quantal size increase counteracts release depression to maintain evoked transmission. The magnitude of the post-tetanic quantal size increase and release depression correlated with stimulation frequency and duration, indicating activity-dependent stabilization of synaptic transmission. The post-tetanic quantal size increase persisted after genetic ablation of the glutamate receptor subunits GluRIIA or GluRIIB, and glutamate receptor calcium permeability, as well as blockade of postsynaptic calcium channels. By contrast, it was strongly attenuated by pharmacological or presynaptic genetic perturbation of the GTPase dynamin. Similar observations were made after inhibition of the H+-ATPase, suggesting that the quantal size increase is presynaptically driven. Additionally, dynamin and H+-ATPase perturbation resulted in a post-tetanic decrease in evoked amplitudes. Finally, we observed an increase in synaptic vesicle diameter after tetanic stimulation. Thus, a presynaptically-driven quantal size increase, likely mediated by larger synaptic vesicles, counterbalances post-tetanic release depression, thereby conferring robustness to synaptic transmission on the minute time scale. KEY POINTS: Many synapses transmit robustly after sustained activity despite the limitation of key resources, such as release-ready synaptic vesicles. We report robust synaptic transmission after sustained high-frequency stimulation of the Drosophila neuromuscular junction despite a reduction in release-ready vesicle number. An increased postsynaptic response to individual vesicles, likely driven by an increase in vesicle size due to endocytosis defects, stabilizes synaptic efficacy for minutes after sustained activity. Our study provides novel insights into the mechanisms governing synaptic stability after sustained neural activity.
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Affiliation(s)
- Anu G Nair
- Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
- Present address: Roche Pharma Research and Early Development, Basel, Switzerland
| | - Nasrin Bollmohr
- Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
- Neuroscience Center Zurich, University of Zurich/ETH Zurich, Zurich, Switzerland
| | - Levin Schökle
- Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
| | - Jennifer Keim
- Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
- Present address: AbbVie AG, Cham, Switzerland
| | | | - Martin Müller
- Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
- Neuroscience Center Zurich, University of Zurich/ETH Zurich, Zurich, Switzerland
- University Research Priority Program (URPP), Adaptive Brain Circuits in Development and Learning (AdaBD), University of Zurich, Zurich, Switzerland
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2
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López-Murcia FJ, Lin KH, Berns MMM, Ranjan M, Lipstein N, Neher E, Brose N, Reim K, Taschenberger H. Complexin has a dual synaptic function as checkpoint protein in vesicle priming and as a promoter of vesicle fusion. Proc Natl Acad Sci U S A 2024; 121:e2320505121. [PMID: 38568977 PMCID: PMC11009659 DOI: 10.1073/pnas.2320505121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Accepted: 03/04/2024] [Indexed: 04/05/2024] Open
Abstract
The presynaptic SNARE-complex regulator complexin (Cplx) enhances the fusogenicity of primed synaptic vesicles (SVs). Consequently, Cplx deletion impairs action potential-evoked transmitter release. Conversely, though, Cplx loss enhances spontaneous and delayed asynchronous release at certain synapse types. Using electrophysiology and kinetic modeling, we show that such seemingly contradictory transmitter release phenotypes seen upon Cplx deletion can be explained by an additional of Cplx in the control of SV priming, where its ablation facilitates the generation of a "faulty" SV fusion apparatus. Supporting this notion, a sequential two-step priming scheme, featuring reduced vesicle fusogenicity and increased transition rates into the faulty primed state, reproduces all aberrations of transmitter release modes and short-term synaptic plasticity seen upon Cplx loss. Accordingly, we propose a dual presynaptic function for the SNARE-complex interactor Cplx, one as a "checkpoint" protein that guarantees the proper assembly of the fusion machinery during vesicle priming, and one in boosting vesicle fusogenicity.
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Affiliation(s)
- Francisco José López-Murcia
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
| | - Kun-Han Lin
- Laboratory of Membrane Biophysics, Max Planck Institute for Multidisciplinary Sciences, Göttingen37077, Germany
| | - Manon M. M. Berns
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
| | - Mrinalini Ranjan
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
- Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences, Georg August University Göttingen, Göttingen37077, Germany
| | - Noa Lipstein
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
| | - Erwin Neher
- Laboratory of Membrane Biophysics, Max Planck Institute for Multidisciplinary Sciences, Göttingen37077, Germany
- Cluster of Excellence ‘Multiscale Bioimaging’, Georg August University Göttingen, Göttingen37073, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
- Cluster of Excellence ‘Multiscale Bioimaging’, Georg August University Göttingen, Göttingen37073, Germany
| | - Kerstin Reim
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
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3
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López-Murcia FJ, Reim K, Taschenberger H. Complexins: Ubiquitously Expressed Presynaptic Regulators of SNARE-Mediated Synaptic Vesicle Fusion. ADVANCES IN NEUROBIOLOGY 2023; 33:255-285. [PMID: 37615870 DOI: 10.1007/978-3-031-34229-5_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitter release is a spatially and temporally tightly regulated process, which requires assembly and disassembly of SNARE complexes to enable the exocytosis of transmitter-loaded synaptic vesicles (SVs) at presynaptic active zones (AZs). While the requirement for the core SNARE machinery is shared by most membrane fusion processes, SNARE-mediated fusion at AZs is uniquely regulated to allow very rapid Ca2+-triggered SV exocytosis following action potential (AP) arrival. To enable a sub-millisecond time course of AP-triggered SV fusion, synapse-specific accessory SNARE-binding proteins are required in addition to the core fusion machinery. Among the known SNARE regulators specific for Ca2+-triggered SV fusion are complexins, which are almost ubiquitously expressed in neurons. This chapter summarizes the structural features of complexins, models for their molecular interactions with SNAREs, and their roles in SV fusion.
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Affiliation(s)
- Francisco José López-Murcia
- Department of Pathology and Experimental Therapy, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Barcelona, Spain.
- Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain.
| | - Kerstin Reim
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
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4
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Abstract
Fundamental discoveries have shaped our molecular understanding of presynaptic processes, such as neurotransmitter release, active zone organization and mechanisms of synaptic vesicle (SV) recycling. However, certain regulatory steps still remain incompletely understood. Protein liquid-liquid phase separation (LLPS) and its role in SV clustering and active zone regulation now introduce a new perception of how the presynapse and its different compartments are organized. This article highlights the newly emerging concept of LLPS at the synapse, providing a systematic overview on LLPS tendencies of over 500 presynaptic proteins, spotlighting individual proteins and discussing recent progress in the field. Newly discovered LLPS systems like ELKS/liprin-alpha and Eps15/FCho are put into context, and further LLPS candidate proteins, including epsin1, dynamin, synaptojanin, complexin and rabphilin-3A, are highlighted.
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Affiliation(s)
- Janin Lautenschläger
- Department of Clinical Neurosciences, Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, UK
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5
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Farsi Z, Walde M, Klementowicz AE, Paraskevopoulou F, Woehler A. Single synapse glutamate imaging reveals multiple levels of release mode regulation in mammalian synapses. iScience 2020; 24:101909. [PMID: 33392479 PMCID: PMC7773578 DOI: 10.1016/j.isci.2020.101909] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 09/24/2020] [Accepted: 12/03/2020] [Indexed: 01/17/2023] Open
Abstract
Mammalian central synapses exhibit vast heterogeneity in signaling strength. To understand the extent of this diversity, how it is achieved, and its functional implications, characterization of a large number of individual synapses is required. Using glutamate imaging, we characterized the evoked release probability and spontaneous release frequency of over 24,000 individual synapses. We found striking variability and no correlation between action potential-evoked and spontaneous synaptic release strength, suggesting distinct regulatory mechanisms. Subpixel localization of individual evoked and spontaneous release events reveals tight spatial regulation of evoked release and enhanced spontaneous release outside of evoked release region. Using on-stage post hoc immune-labeling of vesicle-associated proteins, Ca2+-sensing proteins, and soluble presynaptic proteins we were able to show that distinct molecular ensembles are associated with evoked and spontaneous modes of synaptic release.
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Affiliation(s)
- Zohreh Farsi
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, 10115, Germany
| | - Marie Walde
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, 10115, Germany
| | - Agnieszka E Klementowicz
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, 10115, Germany
| | - Foteini Paraskevopoulou
- Institute of Neurophysiology, NeuroCure Cluster of Excellence, Charité-Universitätsmedizin, Berlin, 10115, Germany
| | - Andrew Woehler
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, 10115, Germany
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6
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Scholz N, Ehmann N, Sachidanandan D, Imig C, Cooper BH, Jahn O, Reim K, Brose N, Meyer J, Lamberty M, Altrichter S, Bormann A, Hallermann S, Pauli M, Heckmann M, Stigloher C, Langenhan T, Kittel RJ. Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix. J Cell Biol 2019; 218:1011-1026. [PMID: 30782781 PMCID: PMC6400551 DOI: 10.1083/jcb.201806155] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 12/14/2018] [Accepted: 01/09/2019] [Indexed: 02/06/2023] Open
Abstract
By performing an in vivo screen in Drosophila melanogaster, Scholz, Ehmann, et al. identify Complexin as a functional interaction partner of Bruchpilot. The two proteins mediate a physical attachment of synaptic vesicles to the active zone cytomatrix and promote rapid, sustained synaptic transmission. Information processing by the nervous system depends on neurotransmitter release from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures via largely unknown protein interactions. The very C-terminal region of Bruchpilot (Brp), a key component of the Drosophila melanogaster CAZ, participates in SV tethering. Here, we identify the conserved SNARE regulator Complexin (Cpx) in an in vivo screen for molecules that link the Brp C terminus to SVs. Brp and Cpx interact genetically and functionally. Both proteins promote SV recruitment to the Drosophila CAZ and counteract short-term synaptic depression. Analyzing SV tethering to active zone ribbons of cpx3 knockout mice supports an evolutionarily conserved role of Cpx upstream of SNARE complex assembly.
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Affiliation(s)
- Nicole Scholz
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany.,Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Leipzig University, Leipzig, Germany
| | - Nadine Ehmann
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany.,Department of Animal Physiology, Institute of Biology, Leipzig University, Leipzig, Germany.,Carl Ludwig Institute for Physiology, Leipzig University, Leipzig, Germany
| | - Divya Sachidanandan
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Olaf Jahn
- Proteomics Group, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Kerstin Reim
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Jutta Meyer
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany.,Proteomics Group, Max Planck Institute of Experimental Medicine, Göttingen, Germany.,Göttingen Graduate School for Neurosciences, Biophysics and Molecular Biosciences, University of Göttingen, Germany
| | - Marius Lamberty
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany.,Department of Animal Physiology, Institute of Biology, Leipzig University, Leipzig, Germany.,Carl Ludwig Institute for Physiology, Leipzig University, Leipzig, Germany
| | - Steffen Altrichter
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany.,Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Leipzig University, Leipzig, Germany
| | - Anne Bormann
- Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Leipzig University, Leipzig, Germany
| | - Stefan Hallermann
- Carl Ludwig Institute for Physiology, Leipzig University, Leipzig, Germany
| | - Martin Pauli
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany
| | - Manfred Heckmann
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany
| | | | - Tobias Langenhan
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany .,Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Leipzig University, Leipzig, Germany
| | - Robert J Kittel
- Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany .,Department of Animal Physiology, Institute of Biology, Leipzig University, Leipzig, Germany.,Carl Ludwig Institute for Physiology, Leipzig University, Leipzig, Germany
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7
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Dhara M, Mohrmann R, Bruns D. v-SNARE function in chromaffin cells. Pflugers Arch 2017; 470:169-180. [PMID: 28887593 PMCID: PMC5748422 DOI: 10.1007/s00424-017-2066-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/28/2017] [Accepted: 08/29/2017] [Indexed: 01/04/2023]
Abstract
Vesicle fusion is elementary for intracellular trafficking and release of signal molecules, thus providing the basis for diverse forms of intercellular communication like hormonal regulation or synaptic transmission. A detailed characterization of the mechanisms underlying exocytosis is key to understand how the nervous system integrates information and generates appropriate responses to stimuli. The machinery for vesicular release employs common molecular players in different model systems including neuronal and neuroendocrine cells, in particular members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) protein family, Sec1/Munc18-like proteins, and other accessory factors. To achieve temporal precision and speed, excitable cells utilize specialized regulatory proteins like synaptotagmin and complexin, whose interplay putatively synchronizes vesicle fusion and enhances stimulus-secretion coupling. In this review, we aim to highlight recent progress and emerging views on the molecular mechanisms, by which constitutively forming SNAREpins are organized in functional, tightly regulated units for synchronized release. Specifically, we will focus on the role of vesicle associated membrane proteins, also referred to as vesicular SNAREs, in fusion and rapid cargo discharge. We will further discuss the functions of SNARE regulators during exocytosis and focus on chromaffin cell as a model system of choice that allows for detailed structure-function analyses and direct measurements of vesicle fusion under precise control of intracellular [Ca]i.
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Affiliation(s)
- Madhurima Dhara
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany
| | - Ralf Mohrmann
- Zentrum für Human- und Molekularbiologie, Saarland University, 66421, Homburg/Saar, Germany
| | - Dieter Bruns
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany.
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8
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C-terminal domain of mammalian complexin-1 localizes to highly curved membranes. Proc Natl Acad Sci U S A 2016; 113:E7590-E7599. [PMID: 27821736 DOI: 10.1073/pnas.1609917113] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In presynaptic nerve terminals, complexin regulates spontaneous "mini" neurotransmitter release and activates Ca2+-triggered synchronized neurotransmitter release. We studied the role of the C-terminal domain of mammalian complexin in these processes using single-particle optical imaging and electrophysiology. The C-terminal domain is important for regulating spontaneous release in neuronal cultures and suppressing Ca2+-independent fusion in vitro, but it is not essential for evoked release in neuronal cultures and in vitro. This domain interacts with membranes in a curvature-dependent fashion similar to a previous study with worm complexin [Snead D, Wragg RT, Dittman JS, Eliezer D (2014) Membrane curvature sensing by the C-terminal domain of complexin. Nat Commun 5:4955]. The curvature-sensing value of the C-terminal domain is comparable to that of α-synuclein. Upon replacement of the C-terminal domain with membrane-localizing elements, preferential localization to the synaptic vesicle membrane, but not to the plasma membrane, results in suppression of spontaneous release in neurons. Membrane localization had no measurable effect on evoked postsynaptic currents of AMPA-type glutamate receptors, but mislocalization to the plasma membrane increases both the variability and the mean of the synchronous decay time constant of NMDA-type glutamate receptor evoked postsynaptic currents.
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9
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N-terminal domain of complexin independently activates calcium-triggered fusion. Proc Natl Acad Sci U S A 2016; 113:E4698-707. [PMID: 27444020 DOI: 10.1073/pnas.1604348113] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Complexin activates Ca(2+)-triggered neurotransmitter release and regulates spontaneous release in the presynaptic terminal by cooperating with the neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and the Ca(2+)-sensor synaptotagmin. The N-terminal domain of complexin is important for activation, but its molecular mechanism is still poorly understood. Here, we observed that a split pair of N-terminal and central domain fragments of complexin is sufficient to activate Ca(2+)-triggered release using a reconstituted single-vesicle fusion assay, suggesting that the N-terminal domain acts as an independent module within the synaptic fusion machinery. The N-terminal domain can also interact independently with membranes, which is enhanced by a cooperative interaction with the neuronal SNARE complex. We show by mutagenesis that membrane binding of the N-terminal domain is essential for activation of Ca(2+)-triggered fusion. Consistent with the membrane-binding property, the N-terminal domain can be substituted by the influenza virus hemagglutinin fusion peptide, and this chimera also activates Ca(2+)-triggered fusion. Membrane binding of the N-terminal domain of complexin therefore cooperates with the other fusogenic elements of the synaptic fusion machinery during Ca(2+)-triggered release.
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10
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Complexin stabilizes newly primed synaptic vesicles and prevents their premature fusion at the mouse calyx of held synapse. J Neurosci 2015; 35:8272-90. [PMID: 26019341 DOI: 10.1523/jneurosci.4841-14.2015] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Complexins (Cplxs) are small synaptic proteins that cooperate with SNARE-complexes in the control of synaptic vesicle (SV) fusion. Studies involving genetic mutation, knock-down, or knock-out indicated two key functions of Cplx that are not mutually exclusive but cannot easily be reconciled, one in facilitating SV fusion, and one in "clamping" SVs to prevent premature fusion. Most studies on the role of Cplxs in mammalian synapse function have relied on cultured neurons, heterologous expression systems, or membrane fusion assays in vitro, whereas little is known about the function of Cplxs in native synapses. We therefore studied consequences of genetic ablation of Cplx1 in the mouse calyx of Held synapse, and discovered a developmentally exacerbating phenotype of reduced spontaneous and evoked transmission but excessive asynchronous release after stimulation, compatible with combined facilitating and clamping functions of Cplx1. Because action potential waveforms, Ca(2+) influx, readily releasable SV pool size, and quantal size were unaltered, the reduced synaptic strength in the absence of Cplx1 is most likely a consequence of a decreased release probability, which is caused, in part, by less tight coupling between Ca(2+) channels and docked SV. We found further that the excessive asynchronous release in Cplx1-deficient calyces triggered aberrant action potentials in their target neurons, and slowed-down the recovery of EPSCs after depleting stimuli. The augmented asynchronous release had a delayed onset and lasted hundreds of milliseconds, indicating that it predominantly represents fusion of newly recruited SVs, which remain unstable and prone to premature fusion in the absence of Cplx1.
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11
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Mohrmann R, Dhara M, Bruns D. Complexins: small but capable. Cell Mol Life Sci 2015; 72:4221-35. [PMID: 26245303 PMCID: PMC4611016 DOI: 10.1007/s00018-015-1998-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 07/09/2015] [Accepted: 07/20/2015] [Indexed: 11/02/2022]
Abstract
Despite intensive research, it is still unclear how an immediate and profound acceleration of exocytosis is triggered by appropriate Ca(2+)-stimuli in presynaptic terminals. This is due to the fact that the molecular mechanisms of "docking" and "priming" reactions, which set up secretory vesicles to fuse at millisecond time scale, are extremely hard to study. Yet, driven by a fruitful combination of in vitro and in vivo analyses, our mechanistic understanding of Ca(2+)-triggered vesicle fusion has certainly advanced in the past few years. In this review, we aim to highlight recent progress and emerging views on the molecular mechanisms, by which constitutively forming SNAREpins are organized in functional, tightly regulated units for synchronized release. In particular, we will focus on the role of the small regulatory factor complexin whose function in Ca(2+)-dependent exocytosis has been controversially discussed for more than a decade. Special emphasis will also be laid on the functional relationship of complexin and synaptotagmin, as both proteins possibly act as allies and/or antagonists to govern SNARE-mediated exocytosis.
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Affiliation(s)
- Ralf Mohrmann
- Zentrum für Human- und Molekularbiologie, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany. .,Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany.
| | - Madhurima Dhara
- Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany
| | - Dieter Bruns
- Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany.
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12
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Martens MB, Celikel T, Tiesinga PHE. A Developmental Switch for Hebbian Plasticity. PLoS Comput Biol 2015; 11:e1004386. [PMID: 26172394 PMCID: PMC4501799 DOI: 10.1371/journal.pcbi.1004386] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 06/08/2015] [Indexed: 12/12/2022] Open
Abstract
Hebbian forms of synaptic plasticity are required for the orderly development of sensory circuits in the brain and are powerful modulators of learning and memory in adulthood. During development, emergence of Hebbian plasticity leads to formation of functional circuits. By modeling the dynamics of neurotransmitter release during early postnatal cortical development we show that a developmentally regulated switch in vesicle exocytosis mode triggers associative (i.e. Hebbian) plasticity. Early in development spontaneous vesicle exocytosis (SVE), often considered as 'synaptic noise', is important for homogenization of synaptic weights and maintenance of synaptic weights in the appropriate dynamic range. Our results demonstrate that SVE has a permissive, whereas subsequent evoked vesicle exocytosis (EVE) has an instructive role in the expression of Hebbian plasticity. A timed onset for Hebbian plasticity can be achieved by switching from SVE to EVE and the balance between SVE and EVE can control the effective rate of Hebbian plasticity. We further show that this developmental switch in neurotransmitter release mode enables maturation of spike-timing dependent plasticity. A mis-timed or inadequate SVE to EVE switch may lead to malformation of brain networks thereby contributing to the etiology of neurodevelopmental disorders. Neurotransmitter release is the principal form of chemical communication in the brain. When an action potential reaches a synapse, calcium influx activates the machinery for neurotransmitter release. During early neuronal development this machinery matures such that neurotransmitter release becomes time-locked to action potentials. By modeling this change in neurotransmitter release, we mechanistically show that the maturation process can be solely responsible for switching on associative (i.e. Hebbian) plasticity in the brain. The relevant proteins of the release machinery can thereby regulate the rate at which neural circuits represent sensory input, providing a novel mechanism to control the learning rate and onset. Appropriately timing of the onset of Hebbian plasticity is important because during early development sensory experience fine-tunes, often irreversibly, the neural wiring in our brain.
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Affiliation(s)
- Marijn B. Martens
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neuroinformatics, Radboud University Nijmegen, Nijmegen, The Netherlands
- * E-mail:
| | - Tansu Celikel
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neurophysiology, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Paul H. E. Tiesinga
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neuroinformatics, Radboud University Nijmegen, Nijmegen, The Netherlands
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13
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Functional roles of complexin in neurotransmitter release at ribbon synapses of mouse retinal bipolar neurons. J Neurosci 2015; 35:4065-70. [PMID: 25740533 DOI: 10.1523/jneurosci.2703-14.2015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ribbon synapses of photoreceptor cells and bipolar neurons in the retina signal graded changes in light intensity via sustained release of neurotransmitter. One molecular specialization of retinal ribbon synapses is the expression of complexin protein subtypes Cplx3 and Cplx4, whereas conventional synapses express Cplx1 and Cplx2. Because complexins bind to the molecular machinery for synaptic vesicle fusion (the SNARE complex) and modulate transmitter release at conventional synapses, we examined the roles of ribbon-specific complexin in regulating release at ribbon synapses of ON bipolar neurons from mouse retina. To interfere acutely with the interaction of native complexins with the SNARE complex, a peptide consisting of the highly conserved SNARE-binding domain of Cplx3 was introduced via a whole-cell patch pipette placed directly on the synaptic terminal, and vesicle fusion was monitored using capacitance measurements and FM-dye destaining. The inhibitory peptide, but not control peptides, increased spontaneous synaptic vesicle fusion, partially depleted reserve synaptic vesicles, and reduced fusion triggered by opening voltage-gated calcium channels under voltage clamp, without affecting the number of synaptic vesicles associated with ribbons, as revealed by electron microscopy of recorded terminals. The results are consistent with a dual role for ribbon-specific complexin, acting as a brake on the SNARE complex to prevent spontaneous fusion in the absence of calcium influx, while at the same time facilitating release evoked by depolarization.
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Dhara M, Yarzagaray A, Schwarz Y, Dutta S, Grabner C, Moghadam PK, Bost A, Schirra C, Rettig J, Reim K, Brose N, Mohrmann R, Bruns D. Complexin synchronizes primed vesicle exocytosis and regulates fusion pore dynamics. ACTA ACUST UNITED AC 2014; 204:1123-40. [PMID: 24687280 PMCID: PMC3971750 DOI: 10.1083/jcb.201311085] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
ComplexinII and SynaptotagminI coordinately transform the constitutively active SNARE-mediated fusion mechanism into a highly synchronized, Ca2+-triggered release apparatus. ComplexinII (CpxII) and SynaptotagminI (SytI) have been implicated in regulating the function of SNARE proteins in exocytosis, but their precise mode of action and potential interplay have remained unknown. In this paper, we show that CpxII increases Ca2+-triggered vesicle exocytosis and accelerates its secretory rates, providing two independent, but synergistic, functions to enhance synchronous secretion. Specifically, we demonstrate that the C-terminal domain of CpxII increases the pool of primed vesicles by hindering premature exocytosis at submicromolar Ca2+ concentrations, whereas the N-terminal domain shortens the secretory delay and accelerates the kinetics of Ca2+-triggered exocytosis by increasing the Ca2+ affinity of synchronous secretion. With its C terminus, CpxII attenuates fluctuations of the early fusion pore and slows its expansion but is functionally antagonized by SytI, enabling rapid transmitter discharge from single vesicles. Thus, our results illustrate how key features of CpxII, SytI, and their interplay transform the constitutively active SNARE-mediated fusion mechanism into a highly synchronized, Ca2+-triggered release apparatus.
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Affiliation(s)
- Madhurima Dhara
- Institute for Physiology, University of Saarland, 66424 Homburg/Saar, Germany
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Wang Z, Wei X, Liu K, Zhang X, Yang F, Zhang H, He Y, Zhu T, Li F, Shi W, Zhang Y, Xu H, Liu J, Yi F. NOX2 deficiency ameliorates cerebral injury through reduction of complexin II-mediated glutamate excitotoxicity in experimental stroke. Free Radic Biol Med 2013; 65:942-951. [PMID: 23982049 DOI: 10.1016/j.freeradbiomed.2013.08.166] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2013] [Revised: 08/12/2013] [Accepted: 08/15/2013] [Indexed: 10/26/2022]
Abstract
Although NADPH oxidase (NOX)-mediated oxidative stress is considered one of the major mechanisms triggering the pathogenic actions of ischemic stroke and very recent studies have indicated that NADPH oxidase is a major source of reactive oxygen species (ROS) production controlling glutamate release, how neuronal NADPH oxidase activation is coupled to glutamate release is not well understood. Therefore, in this study, we used an in vivo transient middle cerebral artery occlusion model and in vitro primary cell cultures to test whether complexins, the regulators of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes necessary for vesicle fusion, are associated with NOX2-derived ROS and contribute to glutamate-mediated excitotoxicity in ischemic stroke. In this study, we first identified the upregulation of complexin II in the ischemic brain and evaluated its potential role in ischemic stroke showing that gene silencing of complexin II ameliorated cerebral injury as evidenced by reduced infarction volume, neurological deficit, and neuron necrosis accompanied by decreased glutamate levels, consistent with the results from NOX2(-/-) mice with ischemic stroke. We further demonstrated that complexin II expression was mediated by NOX2 in primary cultured neurons subjected to oxygen-glucose deprivation (OGD) and contributed to OGD-induced glutamate release and neuron necrosis via SNARE signaling. Taken together, these findings for the first time provide evidence that complexin II is a central target molecule that links NADPH oxidase-derived ROS to glutamate-mediated neuronal excitotoxicity in ischemic stroke.
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Affiliation(s)
- Ziying Wang
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Xinbing Wei
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Kang Liu
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Xiumei Zhang
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Fan Yang
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Hongyu Zhang
- Department of Geriatrics, Qilu Hospital, Shandong University, Jinan, Shandong 250012, China
| | - Yeteng He
- Department of Orthopedics, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong 250014, China
| | - Tianfeng Zhu
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Fengli Li
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Weichen Shi
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Yan Zhang
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Huiyan Xu
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Jiang Liu
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China
| | - Fan Yi
- Department of Pharmacology, School of Medicine, Shandong University, Jinan, Shandong 250012, China.
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Stabilization of spontaneous neurotransmitter release at ribbon synapses by ribbon-specific subtypes of complexin. J Neurosci 2013; 33:8216-26. [PMID: 23658160 DOI: 10.1523/jneurosci.1280-12.2013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ribbon synapses of tonically releasing sensory neurons must provide a large pool of releasable vesicles for sustained release, while minimizing spontaneous release in the absence of stimulation. Complexins are presynaptic proteins that may accomplish this dual task at conventional synapses by interacting with the molecular machinery of synaptic vesicle fusion at the active zone to retard spontaneous vesicle exocytosis yet facilitate release evoked by depolarization. However, ribbon synapses of photoreceptor cells and bipolar neurons in the retina express distinct complexin subtypes, perhaps reflecting the special requirements of these synapses for tonic release. To investigate the role of ribbon-specific complexins in transmitter release, we combined presynaptic voltage clamp, fluorescence imaging, electron microscopy, and behavioral assays of photoreceptive function in zebrafish. Acute interference with complexin function using a peptide derived from the SNARE-binding domain increased spontaneous synaptic vesicle fusion at ribbon synapses of retinal bipolar neurons without affecting release triggered by depolarization. Knockdown of complexin by injection of an antisense morpholino into zebrafish embryos prevented photoreceptor-driven migration of pigment in skin melanophores and caused the pigment distribution to remain in the dark-adapted state even when embryos were exposed to light. This suggests that loss of complexin function elevated spontaneous release in illuminated photoreceptors sufficiently to mimic the higher release rate normally associated with darkness, thus interfering with visual signaling. We conclude that visual system-specific complexins are required for proper illumination-dependent modulation of the rate of neurotransmitter release at visual system ribbon synapses.
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Iyer J, Wahlmark CJ, Kuser-Ahnert GA, Kawasaki F. Molecular mechanisms of COMPLEXIN fusion clamp function in synaptic exocytosis revealed in a new Drosophila mutant. Mol Cell Neurosci 2013; 56:244-54. [PMID: 23769723 DOI: 10.1016/j.mcn.2013.06.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Accepted: 06/03/2013] [Indexed: 11/28/2022] Open
Abstract
The COMPLEXIN (CPX) proteins play a critical role in synaptic vesicle fusion and neurotransmitter release. Previous studies demonstrated that CPX functions in both activation of evoked neurotransmitter release and inhibition/clamping of spontaneous synaptic vesicle fusion. Here we report a new cpx mutant in Drosophila melanogaster, cpx(1257), revealing spatially defined and separable pools of CPX which make distinct contributions to the activation and clamping functions. In cpx(1257), lack of only the last C-terminal amino acid of CPX is predicted to disrupt prenylation and membrane targeting of CPX. Immunocytochemical analysis established localization of wild-type CPX to active zone (AZ) regions containing neurotransmitter release sites as well as broader presynaptic membrane compartments including synaptic vesicles. Parallel biochemical studies confirmed CPX membrane association and demonstrated robust binding interactions of CPX with all three SNAREs. This is in contrast to the cpx(1257) mutant, in which AZ localization of CPX persists but general membrane localization and, surprisingly, the bulk of CPX-SNARE protein interactions are abolished. Furthermore, electrophysiological analysis of neuromuscular synapses revealed interesting differences between cpx(1257) and a cpx null mutant. The cpx null exhibited a marked decrease in the EPSC amplitude, slowed EPSC rise and decay times and an increased mEPSC frequency with respect to wild-type. In contrast, cpx(1257) exhibited a wild-type EPSC with an increased mEPSC frequency and thus a selective failure to clamp spontaneous release. These results indicate that spatially distinct and separable interactions of CPX with presynaptic membranes and SNARE proteins mediate separable activation and clamping functions of CPX in neurotransmitter release.
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Affiliation(s)
- Janani Iyer
- Department of Biology and Center for Molecular Investigation of Neurological Disorders, Penn State University, University Park, PA 16802, United States
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Megighian A, Zordan M, Pantano S, Scorzeto M, Rigoni M, Zanini D, Rossetto O, Montecucco C. Evidence for a radial SNARE super-complex mediating neurotransmitter release at the Drosophila neuromuscular junction. J Cell Sci 2013; 126:3134-40. [PMID: 23687382 DOI: 10.1242/jcs.123802] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The SNARE proteins VAMP/synaptobrevin, SNAP-25 and syntaxin are core components of the apparatus that mediates neurotransmitter release. They form a heterotrimeric complex, and an undetermined number of SNARE complexes assemble to form a super-complex. Here, we present a radial model of this nanomachine. Experiments performed with botulinum neurotoxins led to the identification of one arginine residue in SNAP-25 and one aspartate residue in syntaxin (R206 and D253 in Drosophila melanogaster). These residues are highly conserved and predicted to play a major role in the protein-protein interactions between SNARE complexes by forming an ionic couple. Accordingly, we generated transgenic Drosophila lines expressing SNAREs mutated in these residues and performed an electrophysiological analysis of their neuromuscular junctions. Our results indicate that SNAP-25-R206 and syntaxin-D253 play a major role in neuroexocytosis and support a radial assembly of several SNARE complexes interacting via the ionic couple formed by these two residues.
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Affiliation(s)
- Aram Megighian
- Department of Biomedical Sciences, University of Padova, Via Ugo Bassi 56 B, 35121 Padova, Italy
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Stenovec M, Gonçalves PP, Zorec R. Peptide hormone release monitored from single vesicles in "membrane lawns" of differentiated male pituitary cells: SNAREs and fusion pore widening. Endocrinology 2013; 154:1235-46. [PMID: 23372020 DOI: 10.1210/en.2012-2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In this study we used live-cell immunocytochemistry and confocal microscopy to study the release from a single vesicle in a simplified system called membrane lawns. The lawns were prepared by exposing differentiated pituitary prolactin (PRL)-secreting cells to a hypoosmotic shear stress. The density of the immunolabeled ternary soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) complexes that bind complexin was approximately 10 times lower than the PRL-positive, lawn-resident vesicles; this indicates that some but not all vesicles are associated with ternary SNARE complexes. However, lawn-resident PRL vesicles colocalized relatively well with particular SNARE proteins: synaptobrevin 2 (35%), syntaxin 1 (22%), and 25-kDa synaptosome associated protein (6%). To study vesicle discharge, we prepared lawn-resident vesicles, derived from atrial natriuretic peptide tagged with emerald fluorescent protein (ANP.emd)-transfected cells, which label vesicles. These maintained the structural passage to the exterior because approximately 40% of ANP.emd-loaded vesicles were labeled by extracellular PRL antibodies. Cargo release from the lawn-resident vesicles, monitored by the decline in the ANP.emd fluorescence intensity, was similar to that in intact cells. It is likely that SNARE proteins are required for calcium-dependent release from these vesicles. This is because the expression of the dominant-negative SNARE peptide, which interferes with SNARE complex formation, reduced the number of PRL-positive spots per cell (PRL antibodies placed extracellularly) significantly, from 58 ± 9 to 4 ± 2. In dominant-negative SNARE-treated cells, the PRL-positive area was reduced from 0.259 ± 0.013 to 0.123 ± 0.014 μm(2), which is consistent with a hindered vesicle luminal access for extracellular PRL antibodies. These results indicate that vesicle discharge is regulated by SNARE-mediated fusion pore widening.
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Affiliation(s)
- Matjaž Stenovec
- Celica Biomedical Center, Faculty of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia
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20
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Abstract
Calcium-dependent exocytosis of synaptic vesicles mediates the release of neurotransmitters. Important proteins in this process have been identified such as the SNAREs, synaptotagmins, complexins, Munc18 and Munc13. Structural and functional studies have yielded a wealth of information about the physiological role of these proteins. However, it has been surprisingly difficult to arrive at a unified picture of the molecular sequence of events from vesicle docking to calcium-triggered membrane fusion. Using mainly a biochemical and biophysical perspective, we briefly survey the molecular mechanisms in an attempt to functionally integrate the key proteins into the emerging picture of the neuronal fusion machine.
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Affiliation(s)
- Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
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21
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Abstract
Exocytosis is a multistage process involving a merger between the vesicle and the plasma membranes, leading to the formation of a fusion pore, a channel, through which secretions are released from the vesicle to the cell exterior. A stimulus may influence the pore by either dilating it completely (full-fusion exocytosis) or mediating a reversible closure (transient exocytosis). In neurons, these transitions are short-lived and not accessible for experimentation. However, in some neuroendocrine cells, initial fusion pores may reopen several hundred times, indicating their stability. Moreover, these pores are too narrow to pass luminal molecules to the extracellular space, termed release-unproductive. However, on stimulation, their diameter dilates, initiating the release of cargo without de novo fusion pore formation. To explain the stability of the initial narrow fusion pores, anisotropic membrane constituents with non-axisymmetrical shape were proposed to accumulate in the fusion pore membrane. Although the nature of these is unclear, they may consist of lipids and proteins, including SNAREs, which may facilitate and regulate the pre- and post-fusional stages of exocytosis. In the future, a more detailed insight into the molecular control of fusion pore stabilization and regulation will generate a better understanding of fusion pore physiology in health and disease.
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Mirza N, Vasieva O, Marson AG, Pirmohamed M. Exploring the genomic basis of pharmacoresistance in epilepsy: an integrative analysis of large-scale gene expression profiling studies on brain tissue from epilepsy surgery. Hum Mol Genet 2011; 20:4381-94. [PMID: 21852245 DOI: 10.1093/hmg/ddr365] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Some patients with pharmacoresistant epilepsy undergo therapeutic resection of the epileptic focus. At least 12 large-scale microarray studies on brain tissue from epilepsy surgery have been published over the last 10 years, but they have failed to make a significant impact upon our understanding of pharmacoresistance, because (1) doubts have been raised about their reproducibility, (2) only a small number of the gene expression changes found in each microarray study have been independently validated and (3) the results of different studies have not been integrated to give a coherent picture of the genetic changes involved in epilepsy pharmacoresistance. To overcome these limitations, we (1) assessed the reproducibility of the microarray studies by calculating the overlap between lists of differentially regulated genes from pairs of microarray studies and determining if this was greater than would be expected by chance alone, (2) used an inter-study cross-validation technique to simultaneously verify the expression changes of large numbers of genes and (3) used the combined results of the different microarray studies to perform an integrative analysis based on enriched gene ontology terms, networks and pathways. Using this approach, we respectively (1) demonstrate that there are statistically significant overlaps between the gene expression changes in different publications, (2) verify the differential expression of 233 genes and (3) identify the biological processes, networks and genes likely to be most important in the development of pharmacoresistant epilepsy. Our analysis provides novel biologically plausible candidate genes and pathways which warrant further investigation to assess their causal relevance.
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Affiliation(s)
- Nasir Mirza
- Department of Molecular and Clinical Pharmacology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
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Walter AM, Groffen AJ, Sørensen JB, Verhage M. Multiple Ca2+ sensors in secretion: teammates, competitors or autocrats? Trends Neurosci 2011; 34:487-97. [PMID: 21831459 DOI: 10.1016/j.tins.2011.07.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Revised: 06/21/2011] [Accepted: 07/05/2011] [Indexed: 12/25/2022]
Abstract
Regulated neurotransmitter secretion depends on Ca(2+) sensors, C2 domain proteins that associate with phospholipids and soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) complexes to trigger release upon Ca(2+) binding. Ca(2+) sensors are thought to prevent spontaneous fusion at rest (clamping) and to promote fusion upon Ca(2+) activation. At least eight, often coexpressed, Ca(2+) sensors have been identified in mammals. Accumulating evidence suggests that multiple Ca(2+) sensors interact, rather than work autonomously, to produce the complex secretory response observed in neurons and secretory cells. In this review, we present several working models to describe how different sensors might be arranged to mediate synchronous, asynchronous and spontaneous neurotransmitter release. We discuss the scenario that different Ca(2+) sensors typically act on one shared vesicle pool and compete for binding the multiple SNARE complexes that are likely to assemble at single vesicles, to exert both clamping and fusion-promoting functions.
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Affiliation(s)
- Alexander M Walter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam and VU Medical Center, 1081 HV Amsterdam, The Netherlands
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Kochubey O, Lou X, Schneggenburger R. Regulation of transmitter release by Ca(2+) and synaptotagmin: insights from a large CNS synapse. Trends Neurosci 2011; 34:237-46. [PMID: 21439657 DOI: 10.1016/j.tins.2011.02.006] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 02/17/2011] [Accepted: 02/18/2011] [Indexed: 01/28/2023]
Abstract
Transmitter release at synapses is driven by elevated intracellular Ca(2+) concentration ([Ca(2+)](i)) near the sites of vesicle fusion. [Ca(2+)](i) signals of profoundly different amplitude and kinetics drive the phasic release component during a presynaptic action potential, and asynchronous release at later times. Studies using direct control of [Ca(2+)](i) at a large glutamatergic terminal, the calyx of Held, have provided significant insight into how intracellular Ca(2+) regulates transmitter release over a wide concentration range. Synaptotagmin-2 (Syt2), the major isoform of the Syt1/2 Ca(2+) sensors at these synapses, triggers highly Ca(2+)-cooperative release above 1μM [Ca(2+)](i), but suppresses release at low [Ca(2+)](i). Thus, neurons utilize a highly sophisticated release apparatus to maximize the dynamic range of Ca(2+)-evoked versus spontaneous release.
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Affiliation(s)
- Olexiy Kochubey
- Laboratory of Synaptic Mechanisms, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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