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Gierke K, Lux UT, Regus-Leidig H, Brandstätter JH. The first synapse in vision in the aging mouse retina. Front Cell Neurosci 2023; 17:1291054. [PMID: 38026697 PMCID: PMC10654782 DOI: 10.3389/fncel.2023.1291054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023] Open
Abstract
Vision is our primary sense, and maintaining it throughout our lifespan is crucial for our well-being. However, the retina, which initiates vision, suffers from an age-related, irreversible functional decline. What causes this functional decline, and how it might be treated, is still unclear. Synapses are the functional hub for signal transmission between neurons, and studies have shown that aging is widely associated with synaptic dysfunction. In this study, we examined the first synapse of the visual system - the rod and cone photoreceptor ribbon synapse - in the mouse retina using light and electron microscopy at 2-3 months, ~1 year, and >2 years of age. We asked, whether age-related changes in key synaptic components might be a driver of synaptic dysfunction and ultimately age-related functional decline during normal aging. We found sprouting of horizontal and bipolar cells, formation of ectopic photoreceptor ribbon synapses, and a decrease in the number of rod photoreceptors and photoreceptor ribbon synapses in the aged retina. However, the majority of the photoreceptors did not show obvious changes in the structural components and protein composition of their ribbon synapses. Noteworthy is the increase in mitochondrial size in rod photoreceptor terminals in the aged retina.
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Affiliation(s)
| | | | | | - Johann Helmut Brandstätter
- Animal Physiology/Neurobiology, Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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2
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Nishad R, Betancourt-Solis M, Dey H, Heidelberger R, McNew JA. Regulation of Syntaxin3B-Mediated Membrane Fusion by T14, Munc18, and Complexin. Biomolecules 2023; 13:1463. [PMID: 37892145 PMCID: PMC10604575 DOI: 10.3390/biom13101463] [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: 08/16/2023] [Revised: 09/22/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
Retinal neurons that form ribbon-style synapses operate over a wide dynamic range, continuously relaying visual information to their downstream targets. The remarkable signaling abilities of these neurons are supported by specialized presynaptic machinery, one component of which is syntaxin3B. Syntaxin3B is an essential t-SNARE protein of photoreceptors and bipolar cells that is required for neurotransmitter release. It has a light-regulated phosphorylation site in its N-terminal domain at T14 that has been proposed to modulate membrane fusion. However, a direct test of the latter has been lacking. Using a well-controlled in vitro fusion assay, we found that a phosphomimetic T14 syntaxin3B mutation leads to a small but significant enhancement of SNARE-mediated membrane fusion following the formation of the t-SNARE complex. While the addition of Munc18a had only a minimal effect on membrane fusion mediated by SNARE complexes containing wild-type syntaxin3B, a more significant enhancement was observed in the presence of Munc18a when the SNARE complexes contained a syntaxin3B T14 phosphomimetic mutant. Finally, we showed that the retinal-specific complexins (Cpx III and Cpx IV) inhibited membrane fusion mediated by syntaxin3B-containing SNARE complexes in a dose-dependent manner. Collectively, our results establish that membrane fusion mediated by syntaxin3B-containing SNARE complexes is regulated by the T14 residue of syntaxin3B, Munc18a, and Cpxs III and IV.
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Affiliation(s)
- Rajkishor Nishad
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
| | - Miguel Betancourt-Solis
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
- Lonza Biologics, 14905 Kirby Dr, Houston, TX 77047, USA
| | - Himani Dey
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - James A. McNew
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
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3
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Aldahabi M, Balint F, Holderith N, Lorincz A, Reva M, Nusser Z. Different priming states of synaptic vesicles underlie distinct release probabilities at hippocampal excitatory synapses. Neuron 2022; 110:4144-4161.e7. [PMID: 36261033 PMCID: PMC9796815 DOI: 10.1016/j.neuron.2022.09.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 07/28/2022] [Accepted: 09/27/2022] [Indexed: 12/12/2022]
Abstract
A stunning example of synaptic diversity is the postsynaptic target cell-type-dependent difference in synaptic efficacy in cortical networks. Here, we show that CA1 pyramidal cell (PC) to fast spiking interneuron (FSIN) connections have 10-fold larger release probability (Pv) than those on oriens lacunosum-moleculare (O-LM) interneurons. Freeze-fracture immunolabeling revealed that different nano-topologies and coupling distances between Ca2+ channels and release sites (RSs) are not responsible for the distinct Pv. Although [Ca2+] transients are 40% larger in FSINs innervating boutons, when [Ca2+] entry is matched in the two bouton populations, EPSCs in O-LM cells are still 7-fold smaller. However, application of a phorbol ester analog resulted in a ∼2.5-fold larger augmentation at PC - O-LM compared to PC - FSIN synapses, suggesting incomplete docking or priming of vesicles. Similar densities of docked vesicles rule out distinct RS occupancies and demonstrate that incompletely primed, but docked, vesicles limit the output of PC - O-LM synapses.
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Affiliation(s)
- Mohammad Aldahabi
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary,János Szentágothai School of Neurosciences, Semmelweis University, Budapest, Hungary
| | - Flora Balint
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Noemi Holderith
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Andrea Lorincz
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Maria Reva
- Unit of Synapse and Circuit Dynamics, CNRS UMR 3571, Institute Pasteur, Paris, France
| | - Zoltan Nusser
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary,Corresponding author
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4
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Grabner CP, Jansen I, Neef J, Weihs T, Schmidt R, Riedel D, Wurm CA, Moser T. Resolving the molecular architecture of the photoreceptor active zone with 3D-MINFLUX. SCIENCE ADVANCES 2022; 8:eabl7560. [PMID: 35857490 PMCID: PMC9286502 DOI: 10.1126/sciadv.abl7560] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Cells assemble macromolecular complexes into scaffoldings that serve as substrates for catalytic processes. Years of molecular neurobiology research indicate that neurotransmission depends on such optimization strategies. However, the molecular topography of the presynaptic active zone (AZ), where transmitter is released upon synaptic vesicle (SV) fusion, remains to be visualized. Therefore, we implemented MINFLUX optical nanoscopy to resolve the AZ of rod photoreceptors. This was facilitated by a novel sample immobilization technique that we name heat-assisted rapid dehydration (HARD), wherein a thin layer of rod synaptic terminals (spherules) was transferred onto glass coverslips from fresh retinal slices. Rod ribbon AZs were readily immunolabeled and imaged in 3D with a precision of a few nanometers. Our 3D-MINFLUX results indicate that the SV release site in rods is a molecular complex of bassoon-RIM2-ubMunc13-2-Cav1.4, which repeats longitudinally on both sides of the ribbon.
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Affiliation(s)
- Chad P. Grabner
- Institute for Auditory Neuroscience, University Medical Center Göttingen, 37075 Göttingen, Germany
- Auditory Neuroscience and Synaptic Nanophysiology Group, Max Planck Institute for Multidisciplinary Sciences, 37077 Göttingen, Germany
- Collaborative Research Center 1286, University of Göttingen, Göttingen, Germany
- Cluster of Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells”, University of Göttingen, 37075 Göttingen, Germany
- Corresponding author. (C.P.G.); (C.A.W.); (T.M.)
| | - Isabelle Jansen
- Abberior Instruments, Hans-Adolf-Krebs-Weg 1, 37077 Göttingen, Germany
| | - Jakob Neef
- Institute for Auditory Neuroscience, University Medical Center Göttingen, 37075 Göttingen, Germany
- Auditory Neuroscience and Synaptic Nanophysiology Group, Max Planck Institute for Multidisciplinary Sciences, 37077 Göttingen, Germany
- Collaborative Research Center 1286, University of Göttingen, Göttingen, Germany
- Cluster of Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells”, University of Göttingen, 37075 Göttingen, Germany
| | - Tobias Weihs
- Abberior Instruments, Hans-Adolf-Krebs-Weg 1, 37077 Göttingen, Germany
| | - Roman Schmidt
- Abberior Instruments, Hans-Adolf-Krebs-Weg 1, 37077 Göttingen, Germany
| | - Dietmar Riedel
- Laboratory of Electron Microscopy, Max Planck Institute for Multidisciplinary Sciences, 37077 Göttingen, Germany
| | - Christian A. Wurm
- Abberior Instruments, Hans-Adolf-Krebs-Weg 1, 37077 Göttingen, Germany
- Corresponding author. (C.P.G.); (C.A.W.); (T.M.)
| | - Tobias Moser
- Institute for Auditory Neuroscience, University Medical Center Göttingen, 37075 Göttingen, Germany
- Auditory Neuroscience and Synaptic Nanophysiology Group, Max Planck Institute for Multidisciplinary Sciences, 37077 Göttingen, Germany
- Collaborative Research Center 1286, University of Göttingen, Göttingen, Germany
- Cluster of Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells”, University of Göttingen, 37075 Göttingen, Germany
- Corresponding author. (C.P.G.); (C.A.W.); (T.M.)
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5
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Gething C, Ferrar J, Misra B, Howells G, Andrzejewski AL, Bowen ME, Choi UB. Conformational change of Syntaxin-3b in regulating SNARE complex assembly in the ribbon synapses. Sci Rep 2022; 12:9261. [PMID: 35661757 PMCID: PMC9166750 DOI: 10.1038/s41598-022-09654-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 03/10/2022] [Indexed: 11/09/2022] Open
Abstract
Neurotransmitter release of synaptic vesicles relies on the assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, consisting of syntaxin and SNAP-25 on the plasma membrane and synaptobrevin on the synaptic vesicle. The formation of the SNARE complex progressively zippers towards the membranes, which drives membrane fusion between the plasma membrane and the synaptic vesicle. However, the underlying molecular mechanism of SNARE complex regulation is unclear. In this study, we investigated the syntaxin-3b isoform found in the retinal ribbon synapses using single-molecule fluorescence resonance energy transfer (smFRET) to monitor the conformational changes of syntaxin-3b that modulate the SNARE complex formation. We found that syntaxin-3b is predominantly in a self-inhibiting closed conformation, inefficiently forming the ternary SNARE complex. Conversely, a phosphomimetic mutation (T14E) at the N-terminal region of syntaxin-3b promoted the open conformation, similar to the constitutively open form of syntaxin LE mutant. When syntaxin-3b is bound to Munc18-1, SNARE complex formation is almost completely blocked. Surprisingly, the T14E mutation of syntaxin-3b partially abolishes Munc18-1 regulation, acting as a conformational switch to trigger SNARE complex assembly. Thus, we suggest a model where the conformational change of syntaxin-3b induced by phosphorylation initiates the release of neurotransmitters in the ribbon synapses.
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Affiliation(s)
- Claire Gething
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | - Joshua Ferrar
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | - Bishal Misra
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | - Giovanni Howells
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | | | - Mark E Bowen
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794, USA.,Quantum-Si, Inc, Guilford, CT, 06437, USA
| | - Ucheor B Choi
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA. .,Quantum-Si, Inc, Guilford, CT, 06437, USA.
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6
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A fluorescent nanosensor paint detects dopamine release at axonal varicosities with high spatiotemporal resolution. Proc Natl Acad Sci U S A 2022; 119:e2202842119. [PMID: 35613050 DOI: 10.1073/pnas.2202842119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
SignificanceThe neurotransmitter dopamine controls normal behavior and dopaminergic dysfunction is prevalent in multiple brain diseases. To reach a detailed understanding of how dopamine release and signaling are regulated at the subcellular level, we developed a near infrared fluorescent dopamine nanosensor 'paint' (AndromeDA) to directly image dopamine release and its spatiotemporal characteristics. With AndromeDA, we can ascribe discrete DA release events to defined axonal varicosities, directly assess the heterogeneity of DA release events across such release sites, and determine the molecular components of the DA release machinery. AndromeDA thus provides a new method for gaining fundamental insights into the core mechanisms of dopamine release, which with greatly benefit our knowledge of dopamine biology and pathobiology.
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7
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Vardar G, Salazar-Lázaro A, Zobel S, Trimbuch T, Rosenmund C. Syntaxin-1A modulates vesicle fusion in mammalian neurons via juxtamembrane domain dependent palmitoylation of its transmembrane domain. eLife 2022; 11:78182. [PMID: 35638903 PMCID: PMC9183232 DOI: 10.7554/elife.78182] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 05/30/2022] [Indexed: 11/16/2022] Open
Abstract
SNAREs are undoubtedly one of the core elements of synaptic transmission. Contrary to the well characterized function of their SNARE domains bringing the plasma and vesicular membranes together, the level of contribution of their juxtamembrane domain (JMD) and the transmembrane domain (TMD) to the vesicle fusion is still under debate. To elucidate this issue, we analyzed three groups of STX1A mutations in cultured mouse hippocampal neurons: (1) elongation of STX1A’s JMD by three amino acid insertions in the junction of SNARE-JMD or JMD-TMD; (2) charge reversal mutations in STX1A’s JMD; and (3) palmitoylation deficiency mutations in STX1A’s TMD. We found that both JMD elongations and charge reversal mutations have position-dependent differential effects on Ca2+-evoked and spontaneous neurotransmitter release. Importantly, we show that STX1A’s JMD regulates the palmitoylation of STX1A’s TMD and loss of STX1A palmitoylation either through charge reversal mutation K260E or by loss of TMD cysteines inhibits spontaneous vesicle fusion. Interestingly, the retinal ribbon specific STX3B has a glutamate in the position corresponding to the K260E mutation in STX1A and mutating it with E259K acts as a molecular on-switch. Furthermore, palmitoylation of post-synaptic STX3A can be induced by the exchange of its JMD with STX1A’s JMD together with the incorporation of two cysteines into its TMD. Forced palmitoylation of STX3A dramatically enhances spontaneous vesicle fusion suggesting that STX1A regulates spontaneous release through two distinct mechanisms: one through the C-terminal half of its SNARE domain and the other through the palmitoylation of its TMD.
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Affiliation(s)
- Gülçin Vardar
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Andrea Salazar-Lázaro
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Sina Zobel
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Thorsten Trimbuch
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Christian Rosenmund
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
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8
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Holderith N, Aldahabi M, Nusser Z. Selective Enrichment of Munc13-2 in Presynaptic Active Zones of Hippocampal Pyramidal Cells That Innervate mGluR1α Expressing Interneurons. Front Synaptic Neurosci 2022; 13:773209. [PMID: 35221979 PMCID: PMC8866005 DOI: 10.3389/fnsyn.2021.773209] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/27/2021] [Indexed: 11/13/2022] Open
Abstract
Selective distribution of proteins in presynaptic active zones (AZs) is a prerequisite for generating postsynaptic target cell type-specific differences in presynaptic vesicle release probability (Pv) and short-term plasticity, a characteristic feature of cortical pyramidal cells (PCs). In the hippocampus of rodents, somatostatin and mGluR1α expressing interneurons (mGluR1α+ INs) receive small, facilitating excitatory postsynaptic currents (EPSCs) from PCs and express Elfn1 that trans-synaptically recruits mGluR7 into the presynaptic AZ of PC axons. Here we show that Elfn1 also has a role in the selective recruitment of Munc13-2, a synaptic vesicle priming and docking protein, to PC AZs that innervate mGluR1α+ INs. In Elfn1 knock-out mice, unitary EPSCs (uEPSCs) in mGluR1α+ INs have threefold larger amplitudes with less pronounced short-term facilitation, which might be the consequence of the loss of either mGluR7 or Munc13-2 or both. Conditional genetic deletion of Munc13-2 from CA1 PCs results in the loss of Munc13-2, but not mGluR7 from the AZs, and has no effect on the amplitude of uEPSCs and leaves the characteristic short-term facilitation intact at PC to mGluR1α+ IN connection. Our results demonstrate that Munc13-1 alone is capable of imposing low Pv at PC to mGluR1α+ IN synapses and Munc13-2 has yet an unknown role in this synapse.
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Affiliation(s)
- Noemi Holderith
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
| | - Mohammad Aldahabi
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
- János Szentágothai School of Neurosciences, Semmelweis University, Budapest, Hungary
| | - Zoltan Nusser
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
- *Correspondence: Zoltan Nusser,
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9
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Banerjee A, Imig C, Balakrishnan K, Kershberg L, Lipstein N, Uronen RL, Wang J, Cai X, Benseler F, Rhee JS, Cooper BH, Liu C, Wojcik SM, Brose N, Kaeser PS. Molecular and functional architecture of striatal dopamine release sites. Neuron 2022; 110:248-265.e9. [PMID: 34767769 PMCID: PMC8859508 DOI: 10.1016/j.neuron.2021.10.028] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2020] [Revised: 09/22/2021] [Accepted: 10/19/2021] [Indexed: 01/21/2023]
Abstract
Despite the importance of dopamine for striatal circuit function, mechanistic understanding of dopamine transmission remains incomplete. We recently showed that dopamine secretion relies on the presynaptic scaffolding protein RIM, indicating that it occurs at active zone-like sites similar to classical synaptic vesicle exocytosis. Here, we establish using a systematic gene knockout approach that Munc13 and Liprin-α, active zone proteins for vesicle priming and release site organization, are important for dopamine secretion. Furthermore, RIM zinc finger and C2B domains, which bind to Munc13 and Liprin-α, respectively, are needed to restore dopamine release after RIM ablation. In contrast, and different from typical synapses, the active zone scaffolds RIM-BP and ELKS, and RIM domains that bind to them, are expendable. Hence, dopamine release necessitates priming and release site scaffolding by RIM, Munc13, and Liprin-α, but other active zone proteins are dispensable. Our work establishes that efficient release site architecture mediates fast dopamine exocytosis.
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Affiliation(s)
- Aditi Banerjee
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | | | - Lauren Kershberg
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Noa Lipstein
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Riikka-Liisa Uronen
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Jiexin Wang
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Xintong Cai
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Fritz Benseler
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Jeong Seop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Changliang Liu
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
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10
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Wichmann C, Kuner T. Heterogeneity of glutamatergic synapses: cellular mechanisms and network consequences. Physiol Rev 2022; 102:269-318. [PMID: 34727002 DOI: 10.1152/physrev.00039.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Chemical synapses are commonly known as a structurally and functionally highly diverse class of cell-cell contacts specialized to mediate communication between neurons. They represent the smallest "computational" unit of the brain and are typically divided into excitatory and inhibitory as well as modulatory categories. These categories are subdivided into diverse types, each representing a different structure-function repertoire that in turn are thought to endow neuronal networks with distinct computational properties. The diversity of structure and function found among a given category of synapses is referred to as heterogeneity. The main building blocks for this heterogeneity are synaptic vesicles, the active zone, the synaptic cleft, the postsynaptic density, and glial processes associated with the synapse. Each of these five structural modules entails a distinct repertoire of functions, and their combination specifies the range of functional heterogeneity at mammalian excitatory synapses, which are the focus of this review. We describe synapse heterogeneity that is manifested on different levels of complexity ranging from the cellular morphology of the pre- and postsynaptic cells toward the expression of different protein isoforms at individual release sites. We attempt to define the range of structural building blocks that are used to vary the basic functional repertoire of excitatory synaptic contacts and discuss sources and general mechanisms of synapse heterogeneity. Finally, we explore the possible impact of synapse heterogeneity on neuronal network function.
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Affiliation(s)
- Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Institute for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Thomas Kuner
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, Heidelberg, Germany
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11
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Grabner CP, Moser T. The mammalian rod synaptic ribbon is essential for Ca v channel facilitation and ultrafast synaptic vesicle fusion. eLife 2021; 10:63844. [PMID: 34617508 PMCID: PMC8594941 DOI: 10.7554/elife.63844] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 10/06/2021] [Indexed: 12/19/2022] Open
Abstract
Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal ‘no light detected’ they release glutamate continually to activate post-synaptic receptors. When light is detected glutamate release pauses. How a rod’s individual ribbon enables this process was studied here by recording evoked changes in whole-cell membrane capacitance from wild-type and ribbonless (Ribeye-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca2+-buffer EGTA created a readily releasable pool (RRP) of 87 synaptic vesicles (SVs) that emptied as a single kinetic phase with a τ<0.4 ms. The lower concentration of EGTA accelerated Cav channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Cav channel facilitation; however, Ca2+ channel-release coupling remained tight. These release deficits caused a sharp attenuation of rod-driven scotopic light responses. We conclude that the synaptic ribbon facilitates Ca2+-influx and establishes a large RRP of SVs.
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Affiliation(s)
- Chad Paul Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany.,Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
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12
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Burger CA, Jiang D, Mackin RD, Samuel MA. Development and maintenance of vision's first synapse. Dev Biol 2021; 476:218-239. [PMID: 33848537 DOI: 10.1016/j.ydbio.2021.04.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 04/02/2021] [Accepted: 04/03/2021] [Indexed: 12/21/2022]
Abstract
Synapses in the outer retina are the first information relay points in vision. Here, photoreceptors form synapses onto two types of interneurons, bipolar cells and horizontal cells. Because outer retina synapses are particularly large and highly ordered, they have been a useful system for the discovery of mechanisms underlying synapse specificity and maintenance. Understanding these processes is critical to efforts aimed at restoring visual function through repairing or replacing neurons and promoting their connectivity. We review outer retina neuron synapse architecture, neural migration modes, and the cellular and molecular pathways that play key roles in the development and maintenance of these connections. We further discuss how these mechanisms may impact connectivity in the retina.
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Affiliation(s)
- Courtney A Burger
- Huffington Center on Aging, Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Danye Jiang
- Huffington Center on Aging, Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Robert D Mackin
- Huffington Center on Aging, Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Melanie A Samuel
- Huffington Center on Aging, Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA.
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13
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Thoreson WB. Transmission at rod and cone ribbon synapses in the retina. Pflugers Arch 2021; 473:1469-1491. [PMID: 33779813 DOI: 10.1007/s00424-021-02548-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/23/2021] [Accepted: 02/25/2021] [Indexed: 12/29/2022]
Abstract
Light-evoked voltage responses of rod and cone photoreceptor cells in the vertebrate retina must be converted to a train of synaptic vesicle release events for transmission to downstream neurons. This review discusses the processes, proteins, and structures that shape this critical early step in vision, focusing on studies from salamander retina with comparisons to other experimental animals. Many mechanisms are conserved across species. In cones, glutamate release is confined to ribbon release sites although rods are also capable of release at non-ribbon sites. The role of non-ribbon release in rods remains unclear. Release from synaptic ribbons in rods and cones involves at least three vesicle pools: a readily releasable pool (RRP) matching the number of membrane-associated vesicles along the ribbon base, a ribbon reserve pool matching the number of additional vesicles on the ribbon, and an enormous cytoplasmic reserve. Vesicle release increases in parallel with Ca2+ channel activity. While the opening of only a few Ca2+ channels beneath each ribbon can trigger fusion of a single vesicle, sustained release rates in darkness are governed by the rate at which the RRP can be replenished. The number of vacant release sites, their functional status, and the rate of vesicle delivery in turn govern replenishment. Along with an overview of the mechanisms of exocytosis and endocytosis, we consider specific properties of ribbon-associated proteins and pose a number of remaining questions about this first synapse in the visual system.
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Affiliation(s)
- Wallace B Thoreson
- Truhlsen Eye Institute, Departments of Ophthalmology & Visual Sciences and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.
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14
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Voorn RA, Vogl C. Molecular Assembly and Structural Plasticity of Sensory Ribbon Synapses-A Presynaptic Perspective. Int J Mol Sci 2020; 21:E8758. [PMID: 33228215 PMCID: PMC7699581 DOI: 10.3390/ijms21228758] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 11/16/2020] [Accepted: 11/17/2020] [Indexed: 12/13/2022] Open
Abstract
In the mammalian cochlea, specialized ribbon-type synapses between sensory inner hair cells (IHCs) and postsynaptic spiral ganglion neurons ensure the temporal precision and indefatigability of synaptic sound encoding. These high-through-put synapses are presynaptically characterized by an electron-dense projection-the synaptic ribbon-which provides structural scaffolding and tethers a large pool of synaptic vesicles. While advances have been made in recent years in deciphering the molecular anatomy and function of these specialized active zones, the developmental assembly of this presynaptic interaction hub remains largely elusive. In this review, we discuss the dynamic nature of IHC (pre-) synaptogenesis and highlight molecular key players as well as the transport pathways underlying this process. Since developmental assembly appears to be a highly dynamic process, we further ask if this structural plasticity might be maintained into adulthood, how this may influence the functional properties of a given IHC synapse and how such plasticity could be regulated on the molecular level. To do so, we take a closer look at other ribbon-bearing systems, such as retinal photoreceptors and pinealocytes and aim to infer conserved mechanisms that may mediate these phenomena.
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MESH Headings
- Alcohol Oxidoreductases/genetics
- Alcohol Oxidoreductases/metabolism
- Animals
- Co-Repressor Proteins/genetics
- Co-Repressor Proteins/metabolism
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Cytoskeleton/metabolism
- Cytoskeleton/ultrastructure
- Gene Expression Regulation, Developmental
- Hair Cells, Auditory, Inner/metabolism
- Hair Cells, Auditory, Inner/ultrastructure
- Hair Cells, Auditory, Outer/metabolism
- Hair Cells, Auditory, Outer/ultrastructure
- Hair Cells, Vestibular/metabolism
- Hair Cells, Vestibular/ultrastructure
- Mechanotransduction, Cellular
- Mice
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/metabolism
- Neuronal Plasticity/genetics
- Neuropeptides/genetics
- Neuropeptides/metabolism
- Rats
- Synapses/metabolism
- Synapses/ultrastructure
- Synaptic Transmission/genetics
- Synaptic Vesicles/metabolism
- Synaptic Vesicles/ultrastructure
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Affiliation(s)
- Roos Anouk Voorn
- Presynaptogenesis and Intracellular Transport in Hair Cells Junior Research Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Goettingen, 37075 Goettingen, Germany;
- Göttingen Graduate Center for Neurosciences, Biophysics and Molecular Biosciences, 37075 Goettingen, Germany
- Collaborative Research Center 889 “Cellular Mechanisms of Sensory Processing”, 37075 Goettingen, Germany
| | - Christian Vogl
- Presynaptogenesis and Intracellular Transport in Hair Cells Junior Research Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Goettingen, 37075 Goettingen, Germany;
- Collaborative Research Center 889 “Cellular Mechanisms of Sensory Processing”, 37075 Goettingen, Germany
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15
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Heterogeneous Presynaptic Distribution of Munc13 Isoforms at Retinal Synapses and Identification of an Unconventional Bipolar Cell Type with Dual Expression of Munc13 Isoforms: A Study Using Munc13-EXFP Knock-in Mice. Int J Mol Sci 2020; 21:ijms21217848. [PMID: 33105896 PMCID: PMC7660176 DOI: 10.3390/ijms21217848] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 10/19/2020] [Accepted: 10/20/2020] [Indexed: 12/19/2022] Open
Abstract
Munc13 isoforms are constituents of the presynaptic compartment of chemical synapses, where they govern important steps in preparing synaptic vesicles for exocytosis. The role of Munc13-1, -2 and -3 is well documented in brain neurons, but less is known about their function and distribution among the neurons of the retina and their conventional and ribbon-type chemical synapses. Here, we examined the retinae of Munc13-1-, -2-, and -3-EXFP knock-in (KI) mice with a combination of immunocytochemistry, physiology, and electron microscopy. We show that knock-in of Munc13-EXFP fusion proteins did not affect overall retinal anatomy or synapse structure, but slightly affected synaptic transmission. By labeling Munc13-EXFP KI retinae with specific antibodies against Munc13-1, -2 and -3, we found that unlike in the brain, most retinal synapses seem to operate with a single Munc13 isoform. A surprising exception to this rule was type 6 ON bipolar cells, which expressed two Munc13 isoforms in their synaptic terminals, ubMunc13-2 and Munc13-3. The results of this study provide an important basis for future studies on the contribution of Munc13 isoforms in visual signal processing in the mammalian retina.
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16
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Campbell JR, Li H, Wang Y, Kozhemyakin M, Hunt AJ, Liu X, Janz R, Heidelberger R. Phosphorylation of the Retinal Ribbon Synapse Specific t-SNARE Protein Syntaxin3B Is Regulated by Light via a Ca 2 +-Dependent Pathway. Front Cell Neurosci 2020; 14:587072. [PMID: 33192329 PMCID: PMC7606922 DOI: 10.3389/fncel.2020.587072] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 09/11/2020] [Indexed: 12/27/2022] Open
Abstract
Neurotransmitter release at retinal ribbon-style synapses utilizes a specialized t-SNARE protein called syntaxin3B (STX3B). In contrast to other syntaxins, STX3 proteins can be phosphorylated in vitro at T14 by Ca2+/calmodulin-dependent protein kinase II (CaMKII). This modification has the potential to modulate SNARE complex formation required for neurotransmitter release in an activity-dependent manner. To determine the extent to which T14 phosphorylation occurs in vivo in the mammalian retina and characterize the pathway responsible for the in vivo phosphorylation of T14, we utilized quantitative immunofluorescence to measure the levels of STX3 and STX3 phosphorylated at T14 (pSTX3) in the synaptic terminals of mouse retinal photoreceptors and rod bipolar cells (RBCs). Results demonstrate that STX3B phosphorylation at T14 is light-regulated and dependent upon the elevation of intraterminal Ca2+. In rod photoreceptor terminals, the ratio of pSTX3 to STX3 was significantly higher in dark-adapted mice, when rods are active, than in light-exposed mice. By contrast, in RBC terminals, the ratio of pSTX3 to STX3 was higher in light-exposed mice, when these terminals are active, than in dark-adapted mice. These results were recapitulated in the isolated eyecup preparation, but only when Ca2+ was included in the external medium. In the absence of external Ca2+, pSTX3 levels remained low regardless of light/dark exposure. Using the isolated RBC preparation, we next showed that elevation of intraterminal Ca2+ alone was sufficient to increase STX3 phosphorylation at T14. Furthermore, both the non-specific kinase inhibitor staurosporine and the selective CaMKII inhibitor AIP inhibited the Ca2+-dependent increase in the pSTX3/STX3 ratio in isolated RBC terminals, while in parallel experiments, AIP suppressed RBC depolarization-evoked exocytosis, measured using membrane capacitance measurements. Our data support a novel, illumination-regulated modulation of retinal ribbon-style synapse function in which activity-dependent Ca2+ entry drives the phosphorylation of STX3B at T14 by CaMKII, which in turn, modulates the ability to form SNARE complexes required for exocytosis.
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Affiliation(s)
- Joseph R Campbell
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Hongyan Li
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Yanzhao Wang
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Maxim Kozhemyakin
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Albert J Hunt
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Xiaoqin Liu
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Roger Janz
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
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17
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Moser T, Grabner CP, Schmitz F. Sensory Processing at Ribbon Synapses in the Retina and the Cochlea. Physiol Rev 2020; 100:103-144. [DOI: 10.1152/physrev.00026.2018] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In recent years, sensory neuroscientists have made major efforts to dissect the structure and function of ribbon synapses which process sensory information in the eye and ear. This review aims to summarize our current understanding of two key aspects of ribbon synapses: 1) their mechanisms of exocytosis and endocytosis and 2) their molecular anatomy and physiology. Our comparison of ribbon synapses in the cochlea and the retina reveals convergent signaling mechanisms, as well as divergent strategies in different sensory systems.
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Affiliation(s)
- Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Chad P. Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Frank Schmitz
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
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18
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Falk N, Joachimsthaler A, Kessler K, Lux UT, Noegel AA, Kremers J, Brandstätter JH, Gießl A, Falk N, Joachimsthaler A, Kessler K, Lux UT, Noegel AA, Kremers J, Brandstätter JH, Gießl A. Lack of a Retinal Phenotype in a Syne-2/Nesprin-2 Knockout Mouse Model. Cells 2019; 8:cells8101238. [PMID: 31614616 PMCID: PMC6830317 DOI: 10.3390/cells8101238] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 10/04/2019] [Accepted: 10/10/2019] [Indexed: 01/24/2023] Open
Abstract
Syne-2 (also known as Nesprin-2) is a member of a family of proteins that are found primarily in the outer nuclear membrane, as well as other subcellular compartments. Syne-2 contains a C-terminal KASH transmembrane domain and is part of a protein network that associates the nuclear envelope to the cytoskeleton via the binding to actin filaments. Syne-2 plays a role in nuclear migration, nuclear positioning during retinal development, and in ciliogenesis. In a previous study, we showed a connection between Syne-2 and the multifunctional scaffold protein Pericentrin (Pcnt). The elimination of the interaction of Syne-2 and Pcnt showed defects in nuclear migration and the formation of outer segments during retinal development, as well as disturbances in centrosomal migration at the beginning of ciliogenesis in general. In this study, the Syne-2 KO mouse model Nesprin-2△ABD (Syne-2tm1Ngl, MGI) with special attention to Pcnt and ciliogenesis was analyzed. We show reduced expression of Syne-2 in the retina of the Syne-2 KO mouse but found no significant structural—and only a minor functional—phenotype. For the first time, detailed expression analyses showed an expression of a Syne-2 protein larger than 400 kDa (~750 kDa) in the Syne-2/Nesprin-2 KO mouse. In conclusion, the lack of an overt phenotype in Syne-2/Nesprin-2 KO mice suggests the usage of alternative translational start sites, producing Syne-2 splice variants with an intact Pcnt interaction site. Nevertheless, deletion of the actin-binding site in the Syne-2/Nesprin-2 KO mouse revealed a high variability in scotopic oscillatory potentials assuming a novel function of Syne-2 in synchronizing inner retinal processes.
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Affiliation(s)
- Nathalie Falk
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
| | - Anneka Joachimsthaler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany.
| | - Kristin Kessler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
| | - Uwe Thorsten Lux
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
| | - Angelika Anna Noegel
- Institute of Biochemistry I; Medical Faculty, University Hospital, University of Cologne, 50931 Cologne, Germany.
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany.
| | | | - Andreas Gießl
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany.
| | - Nathalie Falk
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Anneka Joachimsthaler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany
| | - Kristin Kessler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Uwe Thorsten Lux
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Angelika Anna Noegel
- Institute of Biochemistry I; Medical Faculty, University Hospital, University of Cologne, 50931 Cologne, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany
| | | | - Andreas Gießl
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
- Department of Ophthalmology, University Hospital Erlangen, 91054 Erlangen, Germany.
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19
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Chakrabarti R, Wichmann C. Nanomachinery Organizing Release at Neuronal and Ribbon Synapses. Int J Mol Sci 2019; 20:E2147. [PMID: 31052288 PMCID: PMC6539712 DOI: 10.3390/ijms20092147] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 04/26/2019] [Accepted: 04/26/2019] [Indexed: 11/17/2022] Open
Abstract
A critical aim in neuroscience is to obtain a comprehensive view of how regulated neurotransmission is achieved. Our current understanding of synapses relies mainly on data from electrophysiological recordings, imaging, and molecular biology. Based on these methodologies, proteins involved in a synaptic vesicle (SV) formation, mobility, and fusion at the active zone (AZ) membrane have been identified. In the last decade, electron tomography (ET) combined with a rapid freezing immobilization of neuronal samples opened a window for understanding the structural machinery with the highest spatial resolution in situ. ET provides significant insights into the molecular architecture of the AZ and the organelles within the presynaptic nerve terminal. The specialized sensory ribbon synapses exhibit a distinct architecture from neuronal synapses due to the presence of the electron-dense synaptic ribbon. However, both synapse types share the filamentous structures, also commonly termed as tethers that are proposed to contribute to different steps of SV recruitment and exocytosis. In this review, we discuss the emerging views on the role of filamentous structures in SV exocytosis gained from ultrastructural studies of excitatory, mainly central neuronal compared to ribbon-type synapses with a focus on inner hair cell (IHC) ribbon synapses. Moreover, we will speculate on the molecular entities that may be involved in filament formation and hence play a crucial role in the SV cycle.
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Affiliation(s)
- Rituparna Chakrabarti
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37075 Göttingen, Germany.
- Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, 37075 Göttingen, Germany.
- Collaborative Research Center 889 "Cellular Mechanisms of Sensory Processing", 37099 Göttingen, Germany.
| | - Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37075 Göttingen, Germany.
- Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, 37075 Göttingen, Germany.
- Collaborative Research Center 889 "Cellular Mechanisms of Sensory Processing", 37099 Göttingen, Germany.
- Collaborative Research Center 1286 "Quantitative Synaptology", 37099 Göttingen, Germany.
- Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany.
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20
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Zuber B, Lučić V. Molecular architecture of the presynaptic terminal. Curr Opin Struct Biol 2019; 54:129-138. [PMID: 30925443 DOI: 10.1016/j.sbi.2019.01.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 01/11/2019] [Accepted: 01/26/2019] [Indexed: 10/27/2022]
Abstract
Neurotransmitter release at the presynaptic terminal is one of the fundamental processes in neuronal communication. It is a complex process comprising signaling pathways that exert a precise spatio-temporal coordination to prepare and bring synaptic vesicles to exocytosis. While many molecular components involved have been identified, their direct observation at different stages of the neurotransmitter release is lacking. Three-dimensional imaging by electron tomography provided remarkable views of the synaptic vesicles and the cytomatrix. Imaging fully hydrated, vitrified samples allowed a direct visualization, precise localization and a quantitative characterization of pleomorphic synaptic vesicle-bound complexes in situ, as well as the elucidation of their function in the neurotransmitter release.
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Affiliation(s)
- Benoît Zuber
- Institute of Anatomy, University of Bern, Bern 3012, Switzerland
| | - Vladan Lučić
- Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
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21
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A Multiple Piccolino-RIBEYE Interaction Supports Plate-Shaped Synaptic Ribbons in Retinal Neurons. J Neurosci 2019; 39:2606-2619. [PMID: 30696732 DOI: 10.1523/jneurosci.2038-18.2019] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 01/08/2019] [Accepted: 01/08/2019] [Indexed: 01/28/2023] Open
Abstract
Active zones at chemical synapses are highly specialized sites for the regulated release of neurotransmitters. Despite a high degree of active zone protein conservation in vertebrates, every type of chemical synapse expresses a given set of protein isoforms and splice variants adapted to the demands on neurotransmitter release. So far, we know little about how specific active zone proteins contribute to the structural and functional diversity of active zones. In this study, we explored the nanodomain organization of ribbon-type active zones by addressing the significance of Piccolino, the ribbon synapse-specific splice variant of Piccolo, for shaping the ribbon structure. We followed up on previous results, which indicated that rod photoreceptor synaptic ribbons lose their structural integrity in a knockdown of Piccolino. Here, we demonstrate an interaction between Piccolino and the major ribbon component RIBEYE that supports plate-shaped synaptic ribbons in retinal neurons. In a detailed ultrastructural analysis of three different types of retinal ribbon synapses in Piccolo/Piccolino-deficient male and female rats, we show that the absence of Piccolino destabilizes the superstructure of plate-shaped synaptic ribbons, although with variable manifestation in the cell types examined. Our analysis illustrates how the expression of a specific active zone protein splice variant (e.g., Piccolino) contributes to structural diversity of vertebrate active zones.SIGNIFICANCE STATEMENT Retinal ribbon synapses are a specialized type of chemical synapse adapted for the regulated fast and tonic release of neurotransmitter. The hallmark of retinal ribbon synapses is the plate-shaped synaptic ribbon, which extends from the release site into the terminals' cytoplasm and tethers hundreds of synaptic vesicles. Here, we show that Piccolino, the synaptic ribbon specific splice variant of Piccolo, interacts with RIBEYE, the main component of synaptic ribbons. This interaction occurs via several PxDLS-like motifs located at the C terminus of Piccolino, which can connect multiple RIBEYE molecules. Loss of Piccolino disrupts the characteristic plate-shaped structure of synaptic ribbons, indicating a role of Piccolino in synaptic ribbon assembly.
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22
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Unc13: a multifunctional synaptic marvel. Curr Opin Neurobiol 2019; 57:17-25. [PMID: 30690332 DOI: 10.1016/j.conb.2018.12.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 12/18/2018] [Accepted: 12/19/2018] [Indexed: 12/16/2022]
Abstract
Nervous systems are built on synaptic connections, and our understanding of these complex compartments has deepened over the past quarter century as the diverse fields of genetics, molecular biology, physiology, and biochemistry each made significant in-roads into synaptic function. On the presynaptic side, an evolutionarily conserved core fusion apparatus constructed from a handful of proteins has emerged, with Unc13 serving as a hub that coordinates nearly every aspect of synaptic transmission. This review briefly highlights recent studies on diverse aspects of Unc13 function including roles in SNARE assembly and quality control, release site building, calcium channel proximity, and short-term synaptic plasticity.
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23
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Pangrsic T, Vogl C. Balancing presynaptic release and endocytic membrane retrieval at hair cell ribbon synapses. FEBS Lett 2018; 592:3633-3650. [PMID: 30251250 DOI: 10.1002/1873-3468.13258] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 09/18/2018] [Accepted: 09/19/2018] [Indexed: 11/07/2022]
Abstract
The timely and reliable processing of auditory and vestibular information within the inner ear requires highly sophisticated sensory transduction pathways. On a cellular level, these demands are met by hair cells, which respond to sound waves - or alterations in body positioning - by releasing glutamate-filled synaptic vesicles (SVs) from their presynaptic active zones with unprecedented speed and exquisite temporal fidelity, thereby initiating the auditory and vestibular pathways. In order to achieve this, hair cells have developed anatomical and molecular specializations, such as the characteristic and name-giving 'synaptic ribbons' - presynaptically anchored dense bodies that tether SVs prior to release - as well as other unique or unconventional synaptic proteins. The tightly orchestrated interplay between these molecular components enables not only ultrafast exocytosis, but similarly rapid and efficient compensatory endocytosis. So far, the knowledge of how endocytosis operates at hair cell ribbon synapses is limited. In this Review, we summarize recent advances in our understanding of the SV cycle and molecular anatomy of hair cell ribbon synapses, with a focus on cochlear inner hair cells.
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Affiliation(s)
- Tina Pangrsic
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine, University Medical Center Göttingen, Germany
| | - Christian Vogl
- Presynaptogenesis and Intracellular Transport in Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine, University Medical Center Göttingen, Germany
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24
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Falk N, Kessler K, Schramm SF, Boldt K, Becirovic E, Michalakis S, Regus-Leidig H, Noegel AA, Ueffing M, Thiel CT, Roepman R, Brandstätter JH, Gießl A. Functional analyses of Pericentrin and Syne-2 interaction in ciliogenesis. J Cell Sci 2018; 131:jcs.218487. [PMID: 30054381 DOI: 10.1242/jcs.218487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 07/12/2018] [Indexed: 01/31/2023] Open
Abstract
Pericentrin (Pcnt) is a multifunctional scaffold protein and mutations in the human PCNT gene are associated with several diseases, including ciliopathies. Pcnt plays a crucial role in ciliary development in olfactory receptor neurons, but its function in the photoreceptor-connecting cilium is unknown. We downregulated Pcnt in the retina ex vivo and in vivo via a virus-based RNA interference approach to study Pcnt function in photoreceptors. ShRNA-mediated knockdown of Pcnt impaired the development of the connecting cilium and the outer segment of photoreceptors, and caused a nuclear migration defect. In protein interaction screens, we found that the outer nuclear membrane protein Syne-2 (also known as Nesprin-2) is an interaction partner of Pcnt in photoreceptors. Syne-2 is important for positioning murine photoreceptor cell nuclei and for centrosomal migration during early ciliogenesis. CRISPR/Cas9-mediated knockout of Syne-2 in cell culture led to an overexpression and mislocalization of Pcnt and to ciliogenesis defects. Our findings suggest that the Pcnt-Syne-2 complex is important for ciliogenesis and outer segment formation during retinal development and plays a role in nuclear migration.
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Affiliation(s)
- Nathalie Falk
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Kristin Kessler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Sinja-Fee Schramm
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Karsten Boldt
- Division of Experimental Ophthalmology and Medical Proteome Center, Center of Ophthalmology, University of Tübingen, 72074 Tübingen, Germany
| | - Elvir Becirovic
- Center for Integrated Protein Science Munich (CIPSM) at the Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - Stylianos Michalakis
- Center for Integrated Protein Science Munich (CIPSM) at the Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - Hanna Regus-Leidig
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Angelika A Noegel
- Institute of Biochemistry I, Medical Faculty, University Hospital, University of Cologne, 50931 Cologne, Germany
| | - Marius Ueffing
- Division of Experimental Ophthalmology and Medical Proteome Center, Center of Ophthalmology, University of Tübingen, 72074 Tübingen, Germany
| | - Christian T Thiel
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
| | - Ronald Roepman
- Department of Human Genetics, Radboud University Medical Center, Nijmegen 6525 GA, The Netherlands
| | | | - Andreas Gießl
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
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25
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Ventimiglia D, Bargmann CI. Diverse modes of synaptic signaling, regulation, and plasticity distinguish two classes of C. elegans glutamatergic neurons. eLife 2017; 6:31234. [PMID: 29160768 PMCID: PMC5705214 DOI: 10.7554/elife.31234] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 11/20/2017] [Indexed: 11/13/2022] Open
Abstract
Synaptic vesicle release properties vary between neuronal cell types, but in most cases the molecular basis of this heterogeneity is unknown. Here, we compare in vivo synaptic properties of two neuronal classes in the C. elegans central nervous system, using VGLUT-pHluorin to monitor synaptic vesicle exocytosis and retrieval in intact animals. We show that the glutamatergic sensory neurons AWCON and ASH have distinct synaptic dynamics associated with tonic and phasic synaptic properties, respectively. Exocytosis in ASH and AWCON is differentially affected by SNARE-complex regulators that are present in both neurons: phasic ASH release is strongly dependent on UNC-13, whereas tonic AWCON release relies upon UNC-18 and on the protein kinase C homolog PKC-1. Strong stimuli that elicit high calcium levels increase exocytosis and retrieval rates in AWCON, generating distinct tonic and evoked synaptic modes. These results highlight the differential deployment of shared presynaptic proteins in neuronal cell type-specific functions.
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Affiliation(s)
- Donovan Ventimiglia
- Lulu and Anthony Wang Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, United States
| | - Cornelia I Bargmann
- Lulu and Anthony Wang Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, United States
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26
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Datta P, Gilliam J, Thoreson WB, Janz R, Heidelberger R. Two Pools of Vesicles Associated with Synaptic Ribbons Are Molecularly Prepared for Release. Biophys J 2017; 113:2281-2298. [PMID: 28863864 DOI: 10.1016/j.bpj.2017.08.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/28/2017] [Accepted: 08/07/2017] [Indexed: 11/17/2022] Open
Abstract
Neurons that form ribbon-style synapses are specialized for continuous exocytosis. To this end, their synaptic terminals contain numerous synaptic vesicles, some of which are ribbon associated, that have difference susceptibilities for undergoing Ca2+-dependent exocytosis. In this study, we probed the relationship between previously defined vesicle populations and determined their fusion competency with respect to SNARE complex formation. We found that both the rapidly releasing vesicle pool and the releasable vesicle pool of the retinal bipolar cell are situated at the ribbon-style active zones, where they functionally interact. A peptide inhibitor of SNARE complex formation failed to block exocytosis from either pool, suggesting that these two vesicle pools have formed the SNARE complexes necessary for fusion. By contrast, a third, slower component of exocytosis was blocked by the peptide, as was the functional replenishment of vesicle pools, indicating that few vesicles outside of the ribbon-style active zones were initially fusion competent. In cone photoreceptors, similar to bipolar cells, fusion of the initial ribbon-associated synaptic vesicle cohort was not blocked by the SNARE complex-inhibiting peptide, whereas a later phase of exocytosis, attributable to the recruitment and subsequent fusion of vesicles newly arrived at the synaptic ribbons, was blocked. Together, our results support a model in which stimulus-evoked exocytosis in retinal ribbon synapses is SNARE-dependent; where vesicles higher up on the synaptic ribbon replenish the rapidly releasing vesicle pool; and at any given time, there are sufficient SNARE complexes to support the fusion of the entire ribbon-associated cohort of vesicles. An important implication of these results is that ribbon-associated vesicles can form intervesicular SNARE complexes, providing mechanistic insight into compound fusion at ribbon-style synapses.
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Affiliation(s)
- Proleta Datta
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| | - Jared Gilliam
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| | - Roger Janz
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas.
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27
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Analysis of RIM Expression and Function at Mouse Photoreceptor Ribbon Synapses. J Neurosci 2017; 37:7848-7863. [PMID: 28701482 DOI: 10.1523/jneurosci.2795-16.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 05/15/2017] [Accepted: 06/18/2017] [Indexed: 12/18/2022] Open
Abstract
RAB3A-interacting molecule (RIM) proteins are important regulators of transmitter release from active zones. At conventional chemical synapses, RIMs contribute substantially to vesicle priming and docking and their loss reduces the readily releasable pool of synaptic vesicles by up to 75%. The priming function of RIMs is mediated via the formation of a tripartite complex with Munc13 and RAB3A, which brings synaptic vesicles in close proximity to Ca2+ channels and the fusion site and activates Munc13. We reported previously that, at mouse photoreceptor ribbon synapses, vesicle priming is Munc13 independent. In this study, we examined RIM expression, distribution, and function at male and female mouse photoreceptor ribbon synapses. We provide evidence that RIM1α and RIM1β are highly likely absent from mouse photoreceptors and that RIM2α is the major large RIM isoform present at photoreceptor ribbon synapses. We show that mouse photoreceptors predominantly express RIM2 variants that lack the interaction domain for Munc13. Loss of full-length RIM2α in a RIM2α mutant mouse only marginally perturbs photoreceptor synaptic transmission. Our findings therefore strongly argue for a priming mechanism at the photoreceptor ribbon synapse that is independent of the formation of a RIM-Munc13-RAB3A complex and thus provide further evidence for a fundamental difference between photoreceptor ribbon synapses and conventional chemical synapses in synaptic vesicle exocytosis.SIGNIFICANCE STATEMENT RAB3A-interacting molecules 1 and 2 (RIM1/2) are essential regulators of exocytosis. At conventional chemical synapses, their function involves Ca2+ channel clustering and synaptic vesicle priming and docking through interactions with Munc13 and RAB3A, respectively. Examining wild-type and RIM2 mutant mice, we show here that the sensory photoreceptor ribbon synapses most likely lack RIM1 and predominantly express RIM2 variants that lack the interaction domain for Munc13. Our findings demonstrate that the photoreceptor-specific RIM variants are not essential for synaptic vesicle priming at photoreceptor ribbon synapses, which represents a fundamental difference between photoreceptor ribbon synapses and conventional chemical synapses with respect to synaptic vesicle priming mechanisms.
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28
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Functional Roles of Complexin 3 and Complexin 4 at Mouse Photoreceptor Ribbon Synapses. J Neurosci 2017; 36:6651-67. [PMID: 27335398 DOI: 10.1523/jneurosci.4335-15.2016] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 05/10/2016] [Indexed: 01/22/2023] Open
Abstract
UNLABELLED 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. SIGNIFICANCE STATEMENT 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.
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29
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Chehab T, Santos NC, Holthenrich A, Koerdt SN, Disse J, Schuberth C, Nazmi AR, Neeft M, Koch H, Man KNM, Wojcik SM, Martin TFJ, van der Sluijs P, Brose N, Gerke V. A novel Munc13-4/S100A10/annexin A2 complex promotes Weibel-Palade body exocytosis in endothelial cells. Mol Biol Cell 2017; 28:1688-1700. [PMID: 28450451 PMCID: PMC5469611 DOI: 10.1091/mbc.e17-02-0128] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 04/17/2017] [Accepted: 04/18/2017] [Indexed: 11/17/2022] Open
Abstract
The tethering factor Munc13-4 is recruited to Weibel–Palade body (WPB) fusion sites after secretagogue stimulation to promote WPB exocytosis. Annexin A2-S100A10 is a novel Munc13-4 interaction partner assisting Munc13-4 tethering at the plasma membrane. Endothelial cells respond to blood vessel injury by the acute release of the procoagulant von Willebrand factor, which is stored in unique secretory granules called Weibel–Palade bodies (WPBs). Stimulated WPB exocytosis critically depends on their proper recruitment to the plasma membrane, but factors involved in WPB–plasma membrane tethering are not known. Here we identify Munc13-4, a protein mutated in familial hemophagocytic lymphohistiocytosis 3, as a WPB-tethering factor. Munc13-4 promotes histamine-evoked WPB exocytosis and is present on WPBs, and secretagogue stimulation triggers an increased recruitment of Munc13-4 to WPBs and a clustering of Munc13-4 at sites of WPB–plasma membrane contact. We also identify the S100A10 subunit of the annexin A2 (AnxA2)-S100A10 protein complex as a novel Munc13-4 interactor and show that AnxA2-S100A10 participates in recruiting Munc13-4 to WPB fusion sites. These findings indicate that Munc13-4 supports acute WPB exocytosis by tethering WPBs to the plasma membrane via AnxA2-S100A10.
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Affiliation(s)
- Tarek Chehab
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Nina Criado Santos
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Anna Holthenrich
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Sophia N Koerdt
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Jennifer Disse
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Christian Schuberth
- Institute of Cell Dynamics and Imaging, Centre for Molecular Biology of Inflammation, Cells-in-Motion Cluster of Excellence, University of Münster, 48149 Münster, Germany
| | - Ali Reza Nazmi
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
| | - Maaike Neeft
- Department of Cell Biology, Center of Molecular Medicine, University Medical Center Utrecht, 3584 CX Utrecht, Netherlands
| | - Henriette Koch
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Kwun Nok M Man
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Thomas F J Martin
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706
| | - Peter van der Sluijs
- Department of Cell Biology, Center of Molecular Medicine, University Medical Center Utrecht, 3584 CX Utrecht, Netherlands
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Volker Gerke
- Institute of Medical Biochemistry, University of Münster, 48149 Münster, Germany
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30
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Kawabe H, Mitkovski M, Kaeser PS, Hirrlinger J, Opazo F, Nestvogel D, Kalla S, Fejtova A, Verrier SE, Bungers SR, Cooper BH, Varoqueaux F, Wang Y, Nehring RB, Gundelfinger ED, Rosenmund C, Rizzoli SO, Südhof TC, Rhee JS, Brose N. ELKS1 localizes the synaptic vesicle priming protein bMunc13-2 to a specific subset of active zones. J Cell Biol 2017; 216:1143-1161. [PMID: 28264913 PMCID: PMC5379939 DOI: 10.1083/jcb.201606086] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 06/18/2016] [Accepted: 01/10/2017] [Indexed: 12/26/2022] Open
Abstract
Presynaptic active zones (AZs) are unique subcellular structures at neuronal synapses, which contain a network of specific proteins that control synaptic vesicle (SV) tethering, priming, and fusion. Munc13s are core AZ proteins with an essential function in SV priming. In hippocampal neurons, two different Munc13s-Munc13-1 and bMunc13-2-mediate opposite forms of presynaptic short-term plasticity and thus differentially affect neuronal network characteristics. We found that most presynapses of cortical and hippocampal neurons contain only Munc13-1, whereas ∼10% contain both Munc13-1 and bMunc13-2. Whereas the presynaptic recruitment and activation of Munc13-1 depends on Rab3-interacting proteins (RIMs), we demonstrate here that bMunc13-2 is recruited to synapses by the AZ protein ELKS1, but not ELKS2, and that this recruitment determines basal SV priming and short-term plasticity. Thus, synapse-specific interactions of different Munc13 isoforms with ELKS1 or RIMs are key determinants of the molecular and functional heterogeneity of presynaptic AZs.
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Affiliation(s)
- Hiroshi Kawabe
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Miso Mitkovski
- Light Microscopy Facility, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Pascal S Kaeser
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305.,Department of Neurobiology, Harvard Medical School, Boston, MA 02115
| | - Johannes Hirrlinger
- Department of Neurogenetics, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.,Carl Ludwig Institute for Physiology, University of Leipzig, 04109 Leipzig, Germany
| | - Felipe Opazo
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, 37073 Göttingen, Germany.,Center for Biostructural Imaging of Neurodegeneration, University of Göttingen Medical Center, 37073 Göttingen, Germany
| | - Dennis Nestvogel
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Stefan Kalla
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Anna Fejtova
- Department of Neurochemistry and Molecular Biology, Leibniz Institute of Neurobiology, 39118 Magdeburg, Germany.,Research Group Presynaptic Plasticity, Leibniz Institute of Neurobiology and Center for Behavioral Brain Sciences, Otto von Guericke University, 39106 Magdeburg, Germany.,Department of Psychiatry and Psychotherapy, University Hospital, Friedrich Alexander University Erlangen-Nuremberg, 91054 Erlangen, Germany
| | - Sophie E Verrier
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Simon R Bungers
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Frederique Varoqueaux
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Yun Wang
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Ralf B Nehring
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030.,Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030
| | - Eckart D Gundelfinger
- Department of Neurochemistry and Molecular Biology, Leibniz Institute of Neurobiology, 39118 Magdeburg, Germany
| | - Christian Rosenmund
- Neuroscience Research Centre and NeuroCure, Charité, University Medicine Berlin, 10117 Berlin, Germany
| | - Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, 37073 Göttingen, Germany
| | - Thomas C Südhof
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Jeong-Seop Rhee
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
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31
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Lipstein N, Göth M, Piotrowski C, Pagel K, Sinz A, Jahn O. Presynaptic Calmodulin targets: lessons from structural proteomics. Expert Rev Proteomics 2017; 14:223-242. [DOI: 10.1080/14789450.2017.1275966] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Noa Lipstein
- Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
| | - Melanie Göth
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Christine Piotrowski
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Kevin Pagel
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Andrea Sinz
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Olaf Jahn
- Proteomics Group, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
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32
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Imig C, Cooper BH. 3D Analysis of Synaptic Ultrastructure in Organotypic Hippocampal Slice Culture by High-Pressure Freezing and Electron Tomography. Methods Mol Biol 2017; 1538:215-231. [PMID: 27943193 DOI: 10.1007/978-1-4939-6688-2_15] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Transmission electron microscopy serves as a valuable tool for synaptic structure-function analyses aimed at identifying morphological features or modifications associated with specific developmental stages or dysfunctional synaptic states. By utilizing cryo-preparation techniques to minimize the introduction of structural artifacts during sample preparation, and electron tomography to reconstruct the 3D ultrastructural architecture of a synapse, the spatial organization and morphological properties of synaptic organelles and subcompartments can be quantified with unparalleled precision. In this chapter, we present an experimental approach combining organotypic slice culture, high-pressure freezing, automated freeze-substitution, and electron tomography to investigate spatial relationships between synaptic vesicles and active zone release sites in synapses from lethal mouse mutants.
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Affiliation(s)
- Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075, Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075, Göttingen, Germany.
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33
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Netrakanti PR, Cooper BH, Dere E, Poggi G, Winkler D, Brose N, Ehrenreich H. Fast cerebellar reflex circuitry requires synaptic vesicle priming by munc13-3. THE CEREBELLUM 2016; 14:264-83. [PMID: 25617111 PMCID: PMC4441738 DOI: 10.1007/s12311-015-0645-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Munc13-3 is a member of the Munc13 family of synaptic vesicle priming proteins and mainly expressed in cerebellar neurons. Munc13-3 null mutant (Munc13-3−/−) mice show decreased synaptic release probability at parallel fiber to Purkinje cell, granule cell to Golgi cell, and granule cell to basket cell synapses and exhibit a motor learning deficit at highest rotarod speeds. Since we detected Munc13-3 immunoreactivity in the dentate gyrus, as reported here for the first time, and current studies indicated a crucial role for the cerebellum in hippocampus-dependent spatial memory, we systematically investigated Munc13-3−/− mice versus wild-type littermates of both genders with respect to hippocampus-related cognition and a range of basic behaviors, including tests for anxiety, sensory functions, motor performance and balance, sensorimotor gating, social interaction and competence, and repetitive and compulsive behaviors. Neither basic behavior nor hippocampus-dependent cognitive performance, evaluated by Morris water maze, hole board working and reference memory, IntelliCage-based place learning including multiple reversals, and fear conditioning, showed any difference between genotypes. However, consistent with a disturbed cerebellar reflex circuitry, a reliable reduction in the acoustic startle response in both male and female Munc13-3−/− mice was found. To conclude, complete deletion of Munc13-3 leads to a robust decrease in the acoustic startle response. This readout of a fast cerebellar reflex circuitry obviously requires synaptic vesicle priming by Munc13-3 for full functionality, in contrast to other behavioral or cognitive features, where a nearly perfect compensation of Munc13-3 deficiency by related synaptic proteins has to be assumed.
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Affiliation(s)
- Pallavi Rao Netrakanti
- Clinical Neuroscience, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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34
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Abstract
The first synapses transmitting visual information contain an unusual organelle, the ribbon, which is involved in the transport and priming of vesicles to be released at the active zone. The ribbon is one of many design features that allow efficient refilling of the active zone, which in turn enables graded changes in membrane potential to be transmitted using a continuous mode of neurotransmitter release. The ribbon also plays a key role in supplying vesicles for rapid and transient bursts of release that signal fast changes, such as the onset of light. We increasingly understand how the physiological properties of ribbon synapses determine basic transformations of the visual signal and, in particular, how the process of refilling the active zone regulates the gain and adaptive properties of the retinal circuit. The molecular basis of ribbon function is, however, far from clear.
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Affiliation(s)
- Leon Lagnado
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom;
| | - Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Saarland University, Homburg/Saar, Germany;
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35
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Man KNM, Imig C, Walter AM, Pinheiro PS, Stevens DR, Rettig J, Sørensen JB, Cooper BH, Brose N, Wojcik SM. Identification of a Munc13-sensitive step in chromaffin cell large dense-core vesicle exocytosis. eLife 2015; 4. [PMID: 26575293 PMCID: PMC4798968 DOI: 10.7554/elife.10635] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 11/16/2015] [Indexed: 01/16/2023] Open
Abstract
It is currently unknown whether the molecular steps of large dense-core vesicle (LDCV) docking and priming are identical to the corresponding reactions in synaptic vesicle (SV) exocytosis. Munc13s are essential for SV docking and priming, and we systematically analyzed their role in LDCV exocytosis using chromaffin cells lacking individual isoforms. We show that particularly Munc13-2 plays a fundamental role in LDCV exocytosis, but in contrast to synapses lacking Munc13s, the corresponding chromaffin cells do not exhibit a vesicle docking defect. We further demonstrate that ubMunc13-2 and Munc13-1 confer Ca(2+)-dependent LDCV priming with similar affinities, but distinct kinetics. Using a mathematical model, we identify an early LDCV priming step that is strongly dependent upon Munc13s. Our data demonstrate that the molecular steps of SV and LDCV priming are very similar while SV and LDCV docking mechanisms are distinct.
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Affiliation(s)
- Kwun Nok M Man
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | | | - Paulo S Pinheiro
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - David R Stevens
- Department of Physiology, Saarland University, Homburg, Germany
| | - Jens Rettig
- Department of Physiology, Saarland University, Homburg, Germany
| | - Jakob B Sørensen
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - Benjamin H Cooper
- 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
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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36
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Veleri S, Lazar CH, Chang B, Sieving PA, Banin E, Swaroop A. Biology and therapy of inherited retinal degenerative disease: insights from mouse models. Dis Model Mech 2015; 8:109-29. [PMID: 25650393 PMCID: PMC4314777 DOI: 10.1242/dmm.017913] [Citation(s) in RCA: 177] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Retinal neurodegeneration associated with the dysfunction or death of photoreceptors is a major cause of incurable vision loss. Tremendous progress has been made over the last two decades in discovering genes and genetic defects that lead to retinal diseases. The primary focus has now shifted to uncovering disease mechanisms and designing treatment strategies, especially inspired by the successful application of gene therapy in some forms of congenital blindness in humans. Both spontaneous and laboratory-generated mouse mutants have been valuable for providing fundamental insights into normal retinal development and for deciphering disease pathology. Here, we provide a review of mouse models of human retinal degeneration, with a primary focus on diseases affecting photoreceptor function. We also describe models associated with retinal pigment epithelium dysfunction or synaptic abnormalities. Furthermore, we highlight the crucial role of mouse models in elucidating retinal and photoreceptor biology in health and disease, and in the assessment of novel therapeutic modalities, including gene- and stem-cell-based therapies, for retinal degenerative diseases.
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Affiliation(s)
- Shobi Veleri
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Csilla H Lazar
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA. Molecular Biology Center, Interdisciplinary Research Institute on Bio-Nano Sciences, Babes-Bolyai-University, Cluj-Napoca, 400271, Romania
| | - Bo Chang
- The Jackson Laboratory, Bar Harbor, ME 04609, USA
| | - Paul A Sieving
- National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Eyal Banin
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA. Center for Retinal and Macular Degenerations, Department of Ophthalmology, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel
| | - Anand Swaroop
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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Wichmann C, Moser T. Relating structure and function of inner hair cell ribbon synapses. Cell Tissue Res 2015; 361:95-114. [PMID: 25874597 PMCID: PMC4487357 DOI: 10.1007/s00441-014-2102-7] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 12/18/2014] [Indexed: 01/28/2023]
Abstract
In the mammalian cochlea, sound is encoded at synapses between inner hair cells (IHCs) and type I spiral ganglion neurons (SGNs). Each SGN receives input from a single IHC ribbon-type active zone (AZ) and yet SGNs indefatigably spike up to hundreds of Hz to encode acoustic stimuli with submillisecond precision. Accumulating evidence indicates a highly specialized molecular composition and structure of the presynapse, adapted to suit these high functional demands. However, we are only beginning to understand key features such as stimulus-secretion coupling, exocytosis mechanisms, exo-endocytosis coupling, modes of endocytosis and vesicle reformation, as well as replenishment of the readily releasable pool. Relating structure and function has become an important avenue in addressing these points and has been applied to normal and genetically manipulated hair cell synapses. Here, we review some of the exciting new insights gained from recent studies of the molecular anatomy and physiology of IHC ribbon synapses.
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Affiliation(s)
- C. Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Collaborative Research Center 889, University Medical Center Göttingen, Göttingen, Germany
| | - T. Moser
- Collaborative Research Center 889, University Medical Center Göttingen, Göttingen, Germany
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany
- Bernstein Center for Computational Neuroscience, University of Göttingen, Göttingen, Germany
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Vogl C, Cooper BH, Neef J, Wojcik SM, Reim K, Reisinger E, Brose N, Rhee JS, Moser T, Wichmann C. Unconventional molecular regulation of synaptic vesicle replenishment in cochlear inner hair cells. J Cell Sci 2015; 128:638-44. [PMID: 25609709 DOI: 10.1242/jcs.162099] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Ribbon synapses of cochlear inner hair cells (IHCs) employ efficient vesicle replenishment to indefatigably encode sound. In neurons, neuroendocrine and immune cells, vesicle replenishment depends on proteins of the mammalian uncoordinated 13 (Munc13, also known as Unc13) and Ca(2+)-dependent activator proteins for secretion (CAPS) families, which prime vesicles for exocytosis. Here, we tested whether Munc13 and CAPS proteins also regulate exocytosis in mouse IHCs by combining immunohistochemistry with auditory systems physiology and IHC patch-clamp recordings of exocytosis in mice lacking Munc13 and CAPS isoforms. Surprisingly, we did not detect Munc13 or CAPS proteins at IHC presynaptic active zones and found normal IHC exocytosis as well as auditory brainstem responses (ABRs) in Munc13 and CAPS deletion mutants. Instead, we show that otoferlin, a C2-domain protein that is crucial for vesicular fusion and replenishment in IHCs, clusters at the plasma membrane of the presynaptic active zone. Electron tomography of otoferlin-deficient IHC synapses revealed a reduction of short tethers holding vesicles at the active zone, which might be a structural correlate of impaired vesicle priming in otoferlin-deficient IHCs. We conclude that IHCs use an unconventional priming machinery that involves otoferlin.
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Affiliation(s)
- Christian Vogl
- Institute for Auditory Neuroscience and InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Jakob Neef
- Institute for Auditory Neuroscience and InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Kerstin Reim
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Ellen Reisinger
- Molecular Biology of Cochlear Neurotransmission Group, InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, 37073 Göttingen, Germany
| | - Jeong-Seop Rhee
- Neurophysiology Group, Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, 37073 Göttingen, Germany
| | - Carolin Wichmann
- Institute for Auditory Neuroscience and InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany
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39
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Munc13-3 superprimes synaptic vesicles at granule cell-to-basket cell synapses in the mouse cerebellum. J Neurosci 2015; 34:14687-96. [PMID: 25355221 DOI: 10.1523/jneurosci.2060-14.2014] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Munc13-3 is a presynaptic protein implicated in vesicle priming that is strongly expressed in cerebellar granule cells (GCs). Mice deficient of Munc13-3 (Munc13-3(-/-)) show an increased paired-pulse ratio (PPR), which led to the hypothesis that Munc13-3 increases the release probability (pr) of vesicles. In the present study, we analyzed unitary synaptic connections between GCs and basket cells in acute cerebellar slices from wild-type and Munc13-3(-/-) mice. Unitary EPSCs recorded from Munc13-3(-/-) GCs showed normal kinetics and synaptic latency but a significantly increased PPR and fraction of synaptic failures. A quantal analysis revealed that neither the charge of single quanta nor the binominal parameter N were affected by loss of Munc13-3 but that pr was almost halved in Munc13-3(-/-). Neither presynaptic Ca(2+) influx was affected by deletion of Munc13-3 nor replenishment of the readily releasable vesicle pool. However, a high concentration of EGTA led to a reduction in EPSCs that was significantly stronger in Munc13-3(-/-). We conclude that Munc13-3 is responsible for an additional step of molecular and/or positional "superpriming" that substantially increases the efficacy of Ca(2+)-triggered release.
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40
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Van Hook MJ, Parmelee CM, Chen M, Cork KM, Curto C, Thoreson WB. Calmodulin enhances ribbon replenishment and shapes filtering of synaptic transmission by cone photoreceptors. ACTA ACUST UNITED AC 2014; 144:357-78. [PMID: 25311636 PMCID: PMC4210432 DOI: 10.1085/jgp.201411229] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
At the first synapse in the vertebrate visual pathway, light-evoked changes in photoreceptor membrane potential alter the rate of glutamate release onto second-order retinal neurons. This process depends on the synaptic ribbon, a specialized structure found at various sensory synapses, to provide a supply of primed vesicles for release. Calcium (Ca(2+)) accelerates the replenishment of vesicles at cone ribbon synapses, but the mechanisms underlying this acceleration and its functional implications for vision are unknown. We studied vesicle replenishment using paired whole-cell recordings of cones and postsynaptic neurons in tiger salamander retinas and found that it involves two kinetic mechanisms, the faster of which was diminished by calmodulin (CaM) inhibitors. We developed an analytical model that can be applied to both conventional and ribbon synapses and showed that vesicle resupply is limited by a simple time constant, τ = 1/(Dρδs), where D is the vesicle diffusion coefficient, δ is the vesicle diameter, ρ is the vesicle density, and s is the probability of vesicle attachment. The combination of electrophysiological measurements, modeling, and total internal reflection fluorescence microscopy of single synaptic vesicles suggested that CaM speeds replenishment by enhancing vesicle attachment to the ribbon. Using electroretinogram and whole-cell recordings of light responses, we found that enhanced replenishment improves the ability of cone synapses to signal darkness after brief flashes of light and enhances the amplitude of responses to higher-frequency stimuli. By accelerating the resupply of vesicles to the ribbon, CaM extends the temporal range of synaptic transmission, allowing cones to transmit higher-frequency visual information to downstream neurons. Thus, the ability of the visual system to encode time-varying stimuli is shaped by the dynamics of vesicle replenishment at photoreceptor synaptic ribbons.
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Affiliation(s)
- Matthew J Van Hook
- Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198
| | - Caitlyn M Parmelee
- Department of Mathematics, University of Nebraska-Lincoln, Lincoln, NE 68588
| | - Minghui Chen
- Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198 Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198
| | - Karlene M Cork
- Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198 Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198
| | - Carina Curto
- Department of Mathematics, University of Nebraska-Lincoln, Lincoln, NE 68588 Department of Mathematics, The Pennsylvania State University, University Park, State College, PA 16802
| | - Wallace B Thoreson
- Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198 Department of Ophthalmology and Visual Sciences and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198
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41
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Ribic A, Liu X, Crair MC, Biederer T. Structural organization and function of mouse photoreceptor ribbon synapses involve the immunoglobulin protein synaptic cell adhesion molecule 1. J Comp Neurol 2014; 522:900-20. [PMID: 23982969 DOI: 10.1002/cne.23452] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 05/23/2013] [Accepted: 08/14/2013] [Indexed: 11/11/2022]
Abstract
Adhesive interactions in the retina instruct the developmental specification of inner retinal layers. However, potential roles of adhesion in the development and function of photoreceptor synapses remain incompletely understood. This contrasts with our understanding of synapse development in the CNS, which can be guided by select adhesion molecules such as the Synaptic Cell Adhesion Molecule 1 (SynCAM 1/CADM1/nectin-like 2 protein). This immunoglobulin superfamily protein modulates the development and plasticity of classical excitatory synapses. We show here by immunoelectron microscopy and immunoblotting that SynCAM 1 is expressed on mouse rod photoreceptors and their terminals in the outer nuclear and plexiform layers in a developmentally regulated manner. Expression of SynCAM 1 on rods is low in early postnatal stages (P3-P7) but increases after eye opening (P14). In support of functional roles in the photoreceptors, electroretinogram recordings demonstrate impaired responses to light stimulation in SynCAM 1 knockout (KO) mice. In addition, the structural integrity of synapses in the OPL requires SynCAM 1. Quantitative ultrastructural analysis of SynCAM 1 KO retina measured fewer fully assembled, triadic rod ribbon synapses. Furthermore, rod synapse ribbons are shortened in KO mice, and protein levels of Ribeye, a major structural component of ribbons, are reduced in SynCAM 1 KO retina. Together, our results implicate SynCAM 1 in the synaptic organization of the rod visual pathway and provide evidence for novel roles of synaptic adhesion in the structural and functional integrity of ribbon synapses.
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Affiliation(s)
- Adema Ribic
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, 06520-8024
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42
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Regus-Leidig H, Fuchs M, Löhner M, Leist SR, Leal-Ortiz S, Chiodo VA, Hauswirth WW, Garner CC, Brandstätter JH. In vivo knockdown of Piccolino disrupts presynaptic ribbon morphology in mouse photoreceptor synapses. Front Cell Neurosci 2014; 8:259. [PMID: 25232303 PMCID: PMC4153300 DOI: 10.3389/fncel.2014.00259] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Accepted: 08/13/2014] [Indexed: 01/08/2023] Open
Abstract
Piccolo is the largest known cytomatrix protein at active zones of chemical synapses. A growing number of studies on conventional chemical synapses assign Piccolo a role in the recruitment and integration of molecules relevant for both endo- and exocytosis of synaptic vesicles, the dynamic assembly of presynaptic F-actin, as well as the proteostasis of presynaptic proteins, yet a direct function in the structural organization of the active zone has not been uncovered in part due to the expression of multiple alternatively spliced isoforms. We recently identified Piccolino, a Piccolo splice variant specifically expressed in sensory ribbon synapses of the eye and ear. Here we down regulated Piccolino in vivo via an adeno-associated virus-based RNA interference approach and explored the impact on the presynaptic structure of mouse photoreceptor ribbon synapses. Detailed immunocytochemical light and electron microscopical analysis of Piccolino knockdown in photoreceptors revealed a hitherto undescribed photoreceptor ribbon synaptic phenotype with striking morphological changes of synaptic ribbon ultrastructure.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Michaela Fuchs
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Martina Löhner
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Sarah R Leist
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany ; Department of Infection Genetics, Helmholtz Centre for Infection Research Braunschweig, Germany
| | - Sergio Leal-Ortiz
- Department of Psychiatry and Behavioral Sciences, Stanford University Palo Alto, CA, USA
| | - Vince A Chiodo
- Department of Ophthalmology, College of Medicine, University of Florida Gainesville, FL, USA
| | - William W Hauswirth
- Department of Ophthalmology, College of Medicine, University of Florida Gainesville, FL, USA
| | - Craig C Garner
- Department of Psychiatry and Behavioral Sciences, Stanford University Palo Alto, CA, USA ; Deutsches Zentrum für Neurodegenerative Erkrankungen Charité, Berlin, Germany
| | - Johann H Brandstätter
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
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Schmitz F. Presynaptic [Ca(2+)] and GCAPs: aspects on the structure and function of photoreceptor ribbon synapses. Front Mol Neurosci 2014; 7:3. [PMID: 24567702 PMCID: PMC3915146 DOI: 10.3389/fnmol.2014.00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 01/15/2014] [Indexed: 12/21/2022] Open
Abstract
Changes in intracellular calcium ions [Ca2+] play important roles in photoreceptor signaling. Consequently, intracellular [Ca2+] levels need to be tightly controlled. In the light-sensitive outer segments (OS) of photoreceptors, Ca2+ regulates the activity of retinal guanylate cyclases thus playing a central role in phototransduction and light-adaptation by restoring light-induced decreases in cGMP. In the synaptic terminals, changes of intracellular Ca2+ trigger various aspects of neurotransmission. Photoreceptors employ tonically active ribbon synapses that encode light-induced, graded changes of membrane potential into modulation of continuous synaptic vesicle exocytosis. The active zones of ribbon synapses contain large electron-dense structures, synaptic ribbons, that are associated with large numbers of synaptic vesicles. Synaptic coding at ribbon synapses differs from synaptic coding at conventional (phasic) synapses. Recent studies revealed new insights how synaptic ribbons are involved in this process. This review focuses on the regulation of [Ca2+] in presynaptic photoreceptor terminals and on the function of a particular Ca2+-regulated protein, the neuronal calcium sensor protein GCAP2 (guanylate cyclase-activating protein-2) in the photoreceptor ribbon synapse. GCAP2, an EF-hand-containing protein plays multiple roles in the OS and in the photoreceptor synapse. In the OS, GCAP2 works as a Ca2+-sensor within a Ca2+-regulated feedback loop that adjusts cGMP levels. In the photoreceptor synapse, GCAP2 binds to RIBEYE, a component of synaptic ribbons, and mediates Ca2+-dependent plasticity at that site. Possible mechanisms are discussed.
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Affiliation(s)
- Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Homburg/Saar, Saarland University Saarland, Germany
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Regus-Leidig H, Atorf J, Feigenspan A, Kremers J, Maw MA, Brandstätter JH. Photoreceptor degeneration in two mouse models for congenital stationary night blindness type 2. PLoS One 2014; 9:e86769. [PMID: 24466230 PMCID: PMC3897778 DOI: 10.1371/journal.pone.0086769] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/17/2013] [Indexed: 02/02/2023] Open
Abstract
Light-dependent conductance changes of voltage-gated Cav1.4 channels regulate neurotransmitter release at photoreceptor ribbon synapses. Mutations in the human CACNA1F gene encoding the α1F subunit of Cav1.4 channels cause an incomplete form of X-linked congenital stationary night blindness (CSNB2). Many CACNA1F mutations are loss-of-function mutations resulting in non-functional Cav1.4 channels, but some mutations alter the channels’ gating properties and, presumably, disturb Ca2+ influx at photoreceptor ribbon synapses. Notably, a CACNA1F mutation (I745T) was identified in a family with an uncommonly severe CSNB2-like phenotype, and, when expressed in a heterologous system, the mutation was shown to shift the voltage-dependence of channel activation, representing a gain-of-function. To gain insight into the pathomechanism that could explain the severity of this disorder, we generated a mouse model with the corresponding mutation in the murine Cacna1f gene (I756T) and compared it with a mouse model carrying a loss-of-function mutation (ΔEx14–17) in a longitudinal study up to eight months of age. In ΔEx14–17 mutants, the b-wave in the electroretinogram was absent, photoreceptor ribbon synapses were abnormal, and Ca2+ responses to depolarization of photoreceptor terminals were undetectable. In contrast, I756T mutants had a reduced scotopic b-wave, some intact rod ribbon synapses, and a strong, though abnormal, Ca2+ response to depolarization. Both mutants showed a progressive photoreceptor loss, but degeneration was more severe and significantly enhanced in the I756T mutants compared to the ΔEx14–17 mutants.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jenny Atorf
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Andreas Feigenspan
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Marion A. Maw
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
- * E-mail: (MAM); (JHB)
| | - Johann Helmut Brandstätter
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
- * E-mail: (MAM); (JHB)
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Regus-Leidig H, Ott C, Löhner M, Atorf J, Fuchs M, Sedmak T, Kremers J, Fejtová A, Gundelfinger ED, Brandstätter JH. Identification and immunocytochemical characterization of Piccolino, a novel Piccolo splice variant selectively expressed at sensory ribbon synapses of the eye and ear. PLoS One 2013; 8:e70373. [PMID: 23936420 PMCID: PMC3735604 DOI: 10.1371/journal.pone.0070373] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 06/17/2013] [Indexed: 02/03/2023] Open
Abstract
Piccolo is one of the largest cytomatrix proteins present at active zones of chemical synapses, where it is suggested to play a role in recruiting and integrating molecules relevant for both synaptic vesicle exo- and endocytosis. Here we examined the retina of a Piccolo-mutant mouse with a targeted deletion of exon 14 in the Pclo gene. Piccolo deficiency resulted in its profound loss at conventional chemical amacrine cell synapses but retinal ribbon synapses were structurally and functionally unaffected. This led to the identification of a shorter, ribbon-specific Piccolo variant, Piccolino, present in retinal photoreceptor cells, bipolar cells, as well as in inner hair cells of the inner ear. By RT-PCR analysis and the generation of a Piccolino-specific antibody we show that non-splicing of intron 5/6 leads to premature translation termination and generation of the C-terminally truncated protein specifically expressed at active zones of ribbon synapse containing cell types. With in situ proximity ligation assays we provide evidence that this truncation leads to the absence of interaction sites for Bassoon, Munc13, and presumably also ELKS/CAST, RIM2, and the L-type Ca2+ channel which exist in the full-length Piccolo at active zones of conventional chemical synapses. The putative lack of interactions with proteins of the active zone suggests a function of Piccolino at ribbon synapses of sensory neurons different from Piccolo’s function at conventional chemical synapses.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Corinna Ott
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Martina Löhner
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jenny Atorf
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Michaela Fuchs
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Tina Sedmak
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Anna Fejtová
- Leibniz Institute for Neurobiology, Magdeburg, Germany
- Center for Behavioral Brain Science, Magdeburg, Germany
| | - Eckart D. Gundelfinger
- Leibniz Institute for Neurobiology, Magdeburg, Germany
- Center for Behavioral Brain Science, Magdeburg, Germany
| | - Johann H. Brandstätter
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
- * E-mail:
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46
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The Munc13 proteins differentially regulate readily releasable pool dynamics and calcium-dependent recovery at a central synapse. J Neurosci 2013; 33:8336-51. [PMID: 23658173 DOI: 10.1523/jneurosci.5128-12.2013] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Munc13 gene family encodes molecules located at the synaptic active zone that regulate the reliability of synapses to encode information over a wide range of frequencies in response to action potentials. In the CNS, proteins of the Munc13 family are critical in regulating neurotransmitter release and synaptic plasticity. Although Munc13-1 is essential for synaptic transmission, it is paradoxical that Munc13-2 and Munc13-3 are functionally dispensable at some synapses, although their loss in other synapses leads to increases in frequency-dependent facilitation. We addressed this issue at the calyx of Held synapse, a giant glutamatergic synapse that we found to express all these Munc13 isoforms. We studied their roles in the regulation of synaptic transmission and their impact on the reliability of information transfer. Through detailed electrophysiological analyses of Munc13-2, Munc13-3, and Munc13-2-3 knock-out and wild-type mice, we report that the combined loss of Munc13-2 and Munc13-3 led to an increase in the rate of calcium-dependent recovery and a change in kinetics of release of the readily releasable pool. Furthermore, viral-mediated overexpression of a dominant-negative form of Munc13-1 at the calyx demonstrated that these effects are Munc13-1 dependent. Quantitative immunohistochemistry using Munc13-fluorescent protein knock-in mice revealed that Munc13-1 is the most highly expressed Munc13 isoform at the calyx and the only one highly colocalized with Bassoon at the active zone. Based on these data, we conclude that Munc13-2 and Munc13-3 isoforms limit the ability of Munc13-1 to regulate calcium-dependent replenishment of readily releasable pool and slow pool to fast pool conversion in central synapses.
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47
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Nonconserved Ca(2+)/calmodulin binding sites in Munc13s differentially control synaptic short-term plasticity. Mol Cell Biol 2012; 32:4628-41. [PMID: 22966208 DOI: 10.1128/mcb.00933-12] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Munc13s are presynaptic proteins that mediate synaptic vesicle priming and thereby control the size of the readily releasable pool of vesicles. During high synaptic activity, Munc13-1 and its closely related homolog, ubMunc13-2, bind Ca(2+)/calmodulin, resulting in enhanced priming activity and in changes of short-term synaptic plasticity characteristics. Here, we studied whether bMunc13-2 and Munc13-3, two remote isoforms of Munc13-1 with a neuronal subtype-specific expression pattern, mediate synaptic vesicle priming and regulate short-term synaptic plasticity in a Ca(2+)/calmodulin-dependent manner. We identified a single functional Ca(2+)/calmodulin binding site in these isoforms and provide structural evidence that all Munc13s employ a common mode of interaction with calmodulin despite the lack of sequence homology between their Ca(2+)/calmodulin binding sites. Electrophysiological analysis showed that, during high-frequency activity, Ca(2+)/calmodulin binding positively regulates the priming activity of bMunc13-2 and Munc13-3, resulting in an increase in the size of the readily releasable pool of vesicles and subsequently in strong short-term synaptic enhancement of neurotransmission. We conclude that Ca(2+)/calmodulin-dependent regulation of priming activity is structurally and functionally conserved in all Munc13 proteins, and that the composition of Munc13 isoforms in a neuron differentially controls its short-term synaptic plasticity characteristics.
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