1
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Small C, Harper C, Jiang A, Kontaxi C, Pronot M, Yak N, Malapaka A, Davenport EC, Wallis TP, Gormal RS, Joensuu M, Martínez-Mármol R, Cousin MA, Meunier FA. SV2A controls the surface nanoclustering and endocytic recruitment of Syt1 during synaptic vesicle recycling. J Neurochem 2024. [PMID: 39091022 DOI: 10.1111/jnc.16186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Revised: 07/04/2024] [Accepted: 07/06/2024] [Indexed: 08/04/2024]
Abstract
Following exocytosis, the recapture of plasma membrane-stranded vesicular proteins into recycling synaptic vesicles (SVs) is essential for sustaining neurotransmission. Surface clustering of vesicular proteins has been proposed to act as a 'pre-assembly' mechanism for endocytosis that ensures high-fidelity retrieval of SV cargo. Here, we used single-molecule imaging to examine the nanoclustering of synaptotagmin-1 (Syt1) and synaptic vesicle protein 2A (SV2A) in hippocampal neurons. Syt1 forms surface nanoclusters through the interaction of its C2B domain with SV2A, which are sensitive to mutations in this domain (Syt1K326A/K328A) and SV2A knockdown. SV2A co-clustering with Syt1 is reduced by blocking SV2A's cognate interaction with Syt1 (SV2AT84A). Surprisingly, impairing SV2A-Syt1 nanoclustering enhanced the plasma membrane recruitment of key endocytic protein dynamin-1, causing accelerated Syt1 endocytosis, altered intracellular sorting and decreased trafficking of Syt1 to Rab5-positive endocytic compartments. Therefore, SV2A and Syt1 are segregated from the endocytic machinery in surface nanoclusters, limiting dynamin recruitment and negatively regulating Syt1 entry into recycling SVs.
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Affiliation(s)
- Christopher Small
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Callista Harper
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Anmin Jiang
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Christiana Kontaxi
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Marie Pronot
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Nyakuoy Yak
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Anusha Malapaka
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Elizabeth C Davenport
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Merja Joensuu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Ramón Martínez-Mármol
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Michael A Cousin
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
- School of Biomedical Sciences, the University of Queensland, Brisbane, Queensland, Australia
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2
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Asmerian H, Alberts J, Sanetra AM, Diaz AJ, Silm K. Role of adaptor protein complexes in generating functionally distinct synaptic vesicle pools. J Physiol 2024. [PMID: 39034608 DOI: 10.1113/jp286179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Accepted: 07/05/2024] [Indexed: 07/23/2024] Open
Abstract
The synaptic vesicle (SV) cycle ensures the release of neurotransmitters and the replenishment of SVs to sustain neuronal activity. Multiple endocytosis and sorting pathways contribute to the recapture of the SV membrane and proteins after fusion. Adaptor protein (AP) complexes are among the critical components of the SV retrieval machinery. The canonical clathrin adaptor AP2 ensures the replenishment of most SVs across many neuronal populations. An alternative AP1/AP3-dependent process mediates the formation of a subset of SVs that differ from AP2 vesicles in molecular composition and respond preferentially during higher frequency firing. Furthermore, recent studies show that vesicular transporters for different neurotransmitters depend to a different extent on the AP3 pathway and this affects the release properties of the respective neurotransmitters. This review focuses on the current understanding of the AP-dependent molecular and functional diversity among SVs. We also discuss the contribution of these pathways to the regulation of neurotransmitter release across neuronal populations.
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Affiliation(s)
- Hrach Asmerian
- Center for Neural Science and Medicine, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Jacob Alberts
- Center for Neural Science and Medicine, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Anna M Sanetra
- Center for Neural Science and Medicine, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Alexia J Diaz
- Center for Neural Science and Medicine, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Katlin Silm
- Center for Neural Science and Medicine, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Department of Neurology, Cedars-Sinai Medical Center, Los Angeles, CA, USA
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3
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Mehta N, Mondal S, Watson ET, Cui Q, Chapman ER. The juxtamembrane linker of synaptotagmin 1 regulates Ca 2+ binding via liquid-liquid phase separation. Nat Commun 2024; 15:262. [PMID: 38177243 PMCID: PMC10766989 DOI: 10.1038/s41467-023-44414-5] [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: 08/11/2023] [Accepted: 12/12/2023] [Indexed: 01/06/2024] Open
Abstract
Synaptotagmin (syt) 1, a Ca2+ sensor for synaptic vesicle exocytosis, functions in vivo as a multimer. Syt1 senses Ca2+ via tandem C2-domains that are connected to a single transmembrane domain via a juxtamembrane linker. Here, we show that this linker segment harbors a lysine-rich, intrinsically disordered region that is necessary and sufficient to mediate liquid-liquid phase separation (LLPS). Interestingly, condensate formation negatively regulates the Ca2+-sensitivity of syt1. Moreover, Ca2+ and anionic phospholipids facilitate the observed phase separation, and increases in [Ca2+]i promote the fusion of syt1 droplets in living cells. Together, these observations suggest a condensate-mediated feedback loop that serves to fine-tune the ability of syt1 to trigger release, via alterations in Ca2+ binding activity and potentially through the impact of LLPS on membrane curvature during fusion reactions. In summary, the juxtamembrane linker of syt1 emerges as a regulator of syt1 function by driving self-association via LLPS.
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Affiliation(s)
- Nikunj Mehta
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Sayantan Mondal
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
| | - Emma T Watson
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
| | - Edwin R Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA.
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4
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Wu LG, Chan CY. Membrane transformations of fusion and budding. Nat Commun 2024; 15:21. [PMID: 38167896 PMCID: PMC10761761 DOI: 10.1038/s41467-023-44539-7] [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: 06/07/2023] [Accepted: 12/15/2023] [Indexed: 01/05/2024] Open
Abstract
Membrane fusion and budding mediate fundamental processes like intracellular trafficking, exocytosis, and endocytosis. Fusion is thought to open a nanometer-range pore that may subsequently close or dilate irreversibly, whereas budding transforms flat membranes into vesicles. Reviewing recent breakthroughs in real-time visualization of membrane transformations well exceeding this classical view, we synthesize a new model and describe its underlying mechanistic principles and functions. Fusion involves hemi-to-full fusion, pore expansion, constriction and/or closure while fusing vesicles may shrink, enlarge, or receive another vesicle fusion; endocytosis follows exocytosis primarily by closing Ω-shaped profiles pre-formed through the flat-to-Λ-to-Ω-shape transition or formed via fusion. Calcium/SNARE-dependent fusion machinery, cytoskeleton-dependent membrane tension, osmotic pressure, calcium/dynamin-dependent fission machinery, and actin/dynamin-dependent force machinery work together to generate fusion and budding modes differing in pore status, vesicle size, speed and quantity, controls release probability, synchronization and content release rates/amounts, and underlies exo-endocytosis coupling to maintain membrane homeostasis. These transformations, underlying mechanisms, and functions may be conserved for fusion and budding in general.
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Affiliation(s)
- Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA.
| | - Chung Yu Chan
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA
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5
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Mehta N, Mondal S, Watson ET, Cui Q, Chapman ER. The juxtamembrane linker of synaptotagmin 1 regulates Ca 2+ binding via liquid-liquid phase separation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.11.551903. [PMID: 37609296 PMCID: PMC10441399 DOI: 10.1101/2023.08.11.551903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Synaptotagmin (syt) 1, a Ca2+ sensor for synaptic vesicle exocytosis, functions in vivo as a multimer. Syt1 senses Ca2+ via tandem C2-domains that are connected to a single transmembrane domain via a juxtamembrane linker. Here, we show that this linker segment harbors a lysine-rich, intrinsically disordered region that is necessary and sufficient to mediate liquid-liquid phase separation (LLPS). Interestingly, condensate formation negatively regulates the Ca2+-sensitivity of syt1. Moreover, Ca2+ and anionic phospholipids facilitate the observed phase separation, and increases in [Ca2+]i promote the fusion of syt1 droplets in living cells. Together, these observations suggest a condensate-mediated feedback loop that serves to fine-tune the ability of syt1 to trigger release, via alterations in Ca2+ binding activity and potentially through the impact of LLPS on membrane curvature during fusion reactions. In summary, the juxtamembrane linker of syt1 emerges as a regulator of syt1 function by driving self-association via LLPS.
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Affiliation(s)
- Nikunj Mehta
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
| | - Sayantan Mondal
- Department of Chemistry, Boston University, Boston, MA 02215, United States
| | - Emma T. Watson
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA 02215, United States
| | - Edwin R. Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
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6
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Bolz S, Kaempf N, Puchkov D, Krauss M, Russo G, Soykan T, Schmied C, Lehmann M, Müller R, Schultz C, Perrais D, Maritzen T, Haucke V. Synaptotagmin 1-triggered lipid signaling facilitates coupling of exo- and endocytosis. Neuron 2023; 111:3765-3774.e7. [PMID: 37738980 DOI: 10.1016/j.neuron.2023.08.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 06/16/2023] [Accepted: 08/16/2023] [Indexed: 09/24/2023]
Abstract
Exocytosis and endocytosis are essential physiological processes and are of prime importance for brain function. Neurotransmission depends on the Ca2+-triggered exocytosis of synaptic vesicles (SVs). In neurons, exocytosis is spatiotemporally coupled to the retrieval of an equal amount of membrane and SV proteins by compensatory endocytosis. How exocytosis and endocytosis are balanced to maintain presynaptic membrane homeostasis and, thereby, sustain brain function is essentially unknown. We combine mouse genetics with optical imaging to show that the SV calcium sensor Synaptotagmin 1 couples exocytic SV fusion to the endocytic retrieval of SV membranes by promoting the local activity-dependent formation of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at presynaptic sites. Interference with these mechanisms impairs PI(4,5)P2-triggered SV membrane retrieval but not exocytic SV fusion. Our findings demonstrate that the coupling of SV exocytosis and endocytosis involves local Synaptotagmin 1-induced lipid signaling to maintain presynaptic membrane homeostasis in central nervous system neurons.
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Affiliation(s)
- Svenja Bolz
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Natalie Kaempf
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Dmytro Puchkov
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Michael Krauss
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Giulia Russo
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Tolga Soykan
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Christopher Schmied
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Martin Lehmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Rainer Müller
- European Molecular Biology Laboratory (EMBL), Cell Biology and Biophysics Unit, 69117 Heidelberg, Germany
| | - Carsten Schultz
- European Molecular Biology Laboratory (EMBL), Cell Biology and Biophysics Unit, 69117 Heidelberg, Germany; Department of Chemical Physiology & Biochemistry, Oregon Health & Science University (OHSU), Portland, OR 97239, USA
| | - David Perrais
- University of Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, 33000 Bordeaux, France
| | - Tanja Maritzen
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany; Department of Nanophysiology, University of Kaiserslautern-Landau, 67663 Kaiserslautern, Germany
| | - Volker Haucke
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany; Faculty of Biology, Chemistry, Pharmacy, Freie Universität Berlin, 14195 Berlin, Germany; NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
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7
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Courtney KC, Mandal T, Mehta N, Wu L, Li Y, Das D, Cui Q, Chapman ER. Synaptotagmin-7 outperforms synaptotagmin-1 to promote the formation of large, stable fusion pores via robust membrane penetration. Nat Commun 2023; 14:7761. [PMID: 38012142 PMCID: PMC10681989 DOI: 10.1038/s41467-023-42497-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 10/11/2023] [Indexed: 11/29/2023] Open
Abstract
Synaptotagmin-1 and synaptotagmin-7 are two prominent calcium sensors that regulate exocytosis in neuronal and neuroendocrine cells. Upon binding calcium, both proteins partially penetrate lipid bilayers that bear anionic phospholipids, but the specific underlying mechanisms that enable them to trigger exocytosis remain controversial. Here, we examine the biophysical properties of these two synaptotagmin isoforms and compare their interactions with phospholipid membranes. We discover that synaptotagmin-1-membrane interactions are greatly influenced by membrane order; tight packing of phosphatidylserine inhibits binding due to impaired membrane penetration. In contrast, synaptotagmin-7 exhibits robust membrane binding and penetration activity regardless of phospholipid acyl chain structure. Thus, synaptotagmin-7 is a super-penetrator. We exploit these observations to specifically isolate and examine the role of membrane penetration in synaptotagmin function. Using nanodisc-black lipid membrane electrophysiology, we demonstrate that membrane penetration is a critical component that underlies how synaptotagmin proteins regulate reconstituted, exocytic fusion pores in response to calcium.
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Affiliation(s)
- Kevin C Courtney
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA
- Department of Biochemistry and Molecular Medicine, West Virginia University, Morgantown, WV, 26506, USA
| | - Taraknath Mandal
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
- Department of Physics, Indian Institute of Technology - Kanpur, Kanpur, 208016, India
| | - Nikunj Mehta
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - Lanxi Wu
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - Yueqi Li
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA
- Center for Bioanalytical Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Debasis Das
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Navy Nagar, Colaba, Mumbai, 400005, India
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
| | - Edwin R Chapman
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, 1111 Highland Avenue, Madison, WI, 53705, USA.
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8
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Turrel O, Ramesh N, Escher MJF, Pooryasin A, Sigrist SJ. Transient active zone remodeling in the Drosophila mushroom body supports memory. Curr Biol 2022; 32:4900-4913.e4. [PMID: 36327980 DOI: 10.1016/j.cub.2022.10.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 08/15/2022] [Accepted: 10/06/2022] [Indexed: 11/22/2022]
Abstract
Elucidating how the distinct components of synaptic plasticity dynamically orchestrate the distinct stages of memory acquisition and maintenance within neuronal networks remains a major challenge. Specifically, plasticity processes tuning the functional and also structural state of presynaptic active zone (AZ) release sites are widely observed in vertebrates and invertebrates, but their behavioral relevance remains mostly unclear. We here provide evidence that a transient upregulation of presynaptic AZ release site proteins supports aversive olfactory mid-term memory in the Drosophila mushroom body (MB). Upon paired aversive olfactory conditioning, AZ protein levels (ELKS-family BRP/(m)unc13-family release factor Unc13A) increased for a few hours with MB-lobe-specific dynamics. Kenyon cell (KC, intrinsic MB neurons)-specific knockdown (KD) of BRP did not affect aversive olfactory short-term memory (STM) but strongly suppressed aversive mid-term memory (MTM). Different proteins crucial for the transport of AZ biosynthetic precursors (transport adaptor Aplip1/Jip-1; kinesin motor IMAC/Unc104; small GTPase Arl8) were also specifically required for the formation of aversive olfactory MTM. Consistent with the merely transitory increase of AZ proteins, BRP KD did not interfere with the formation of aversive olfactory long-term memory (LTM; i.e., 1 day). Our data suggest that the remodeling of presynaptic AZ refines the MB circuitry after paired aversive conditioning, over a time window of a few hours, to display aversive olfactory memories.
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Affiliation(s)
- Oriane Turrel
- Institute for Biology/Genetics, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany
| | - Niraja Ramesh
- Institute for Biology/Genetics, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany
| | - Marc J F Escher
- Institute for Biology/Genetics, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany
| | - Atefeh Pooryasin
- Institute for Biology/Genetics, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany
| | - Stephan J Sigrist
- Institute for Biology/Genetics, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany; NeuroCure Cluster of Excellence, Charité Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany.
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9
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Abstract
Precise and efficient coupling of endocytosis to exocytosis is critical for neurotransmission. The activity-dependent facilitation of endocytosis has been well established for efficient membrane retrieval; however, whether neural activity clamps endocytosis to avoid excessive membrane retrieval remains debatable with the mechanisms largely unknown. The present work provides compelling evidence that synaptotagmin-1 (Syt1) functions as a primary bidirectional Ca2+ sensor to promote slow, small-sized clathrin-mediated endocytosis but inhibit the fast, large-sized bulk endocytosis during elevated neural activity, the disruption of which leads to inefficient vesicle recycling under mild stimulation but excessive membrane retrieval following sustained neurotransmission. Thus, Syt1 serves as a fine-tuning Ca2+ sensor to ensure both efficient and precise coupling of endocytosis to exocytosis in response to different neural activities. Exocytosis and endocytosis are tightly coupled. In addition to initiating exocytosis, Ca2+ plays critical roles in exocytosis–endocytosis coupling in neurons and nonneuronal cells. Both positive and negative roles of Ca2+ in endocytosis have been reported; however, Ca2+ inhibition in endocytosis remains debatable with unknown mechanisms. Here, we show that synaptotagmin-1 (Syt1), the primary Ca2+ sensor initiating exocytosis, plays bidirectional and opposite roles in exocytosis–endocytosis coupling by promoting slow, small-sized clathrin-mediated endocytosis but inhibiting fast, large-sized bulk endocytosis. Ca2+-binding ability is required for Syt1 to regulate both types of endocytic pathways, the disruption of which leads to inefficient vesicle recycling under mild stimulation and excessive membrane retrieval following intense stimulation. Ca2+-dependent membrane tubulation may explain the opposite endocytic roles of Syt1 and provides a general membrane-remodeling working model for endocytosis determination. Thus, Syt1 is a primary bidirectional Ca2+ sensor facilitating clathrin-mediated endocytosis but clamping bulk endocytosis, probably by manipulating membrane curvature to ensure both efficient and precise coupling of endocytosis to exocytosis.
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10
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Benincore-Flórez E, El-Azaz J, Solarte GA, Rodríguez A, Reyes LH, Alméciga-Díaz CJ, Cardona C. Iduronate-2-sulfatase interactome: Validation by Yeast Two-Hybrid Assay. Heliyon 2022; 8:e09031. [PMID: 35284671 PMCID: PMC8913312 DOI: 10.1016/j.heliyon.2022.e09031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 12/08/2021] [Accepted: 02/24/2022] [Indexed: 11/25/2022] Open
Abstract
Mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome, is a rare X-linked recessive disease caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS), which activates intracellular accumulation of nonmetabolized glycosaminoglycans such as heparan sulfate and dermatan sulfate. This accumulation causes severe damage to several tissues, principally the central nervous system. Previously, we identified 187 IDS-protein interactions in the mouse brain. To validate a subset of these interactions, we selected and cloned the coding regions of 10 candidate genes to perform a targeted yeast two-hybrid assay. The results allowed the identification of the physical interaction of IDS with LSAMP and SYT1. Although the physiological relevance of these complexes is unknown, recent advances allow us to point out that these interactions could be involved in vesicular trafficking of IDS through the interaction with SYT1, as well as to the ability to form a transcytosis module between the cellular components of the blood-brain-barrier (BBB) through its interaction with LSAMP. These results may shed light on the role of IDS on cellular homeostasis and may also contribute to the understanding of MPS II physiopathology and the development of novel therapeutic strategies to transport recombinant IDS through the brain endothelial cells toward the brain parenchyma.
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11
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Synaptotagmin 1 oligomerization via the juxtamembrane linker regulates spontaneous and evoked neurotransmitter release. Proc Natl Acad Sci U S A 2021; 118:2113859118. [PMID: 34810248 PMCID: PMC8694047 DOI: 10.1073/pnas.2113859118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2021] [Indexed: 11/18/2022] Open
Abstract
Synaptotagmin 1 (syt1) is a synaptic vesicle (SV) protein that is rapidly activated by Ca2+ influx into presynaptic nerve terminals, triggering SV exocytosis. Syt1 also inhibits exocytosis, prior to Ca2+ influx, and thus helps synchronize evoked exocytosis upon Ca2+ binding. Herein, we identified a cluster of lysine residues, in the oft-ignored juxtamembrane linker region of syt1, that governs homo-multimerization in an anionic lipid-dependent manner. Neutralization of this positively charged region abolished syt1 self-association on phospholipid bilayers in vitro. Subsequently, in neurons, we found mutations that disrupted syt1 self-association were correlated with defects in clamping spontaneous SV release and in triggering and synchronizing evoked exocytosis. Thus, syt1 regulates SV exocytosis as an oligomer via charged residues in the juxtamembrane linker. Synaptotagmin 1 (syt1) is a Ca2+ sensor that regulates synaptic vesicle exocytosis. Cell-based experiments suggest that syt1 functions as a multimer; however, biochemical and electron microscopy studies have yielded contradictory findings regarding putative self-association. Here, we performed dynamic light scattering on syt1 in solution, followed by electron microscopy, and we used atomic force microscopy to study syt1 self-association on supported lipid bilayers under aqueous conditions. Ring-like multimers were clearly observed. Multimerization was enhanced by Ca2+ and required anionic phospholipids. Large ring-like structures (∼180 nm) were reduced to smaller rings (∼30 nm) upon neutralization of a cluster of juxtamembrane lysine residues; further substitution of residues in the second C2-domain completely abolished self-association. When expressed in neurons, syt1 mutants with graded reductions in self-association activity exhibited concomitant reductions in 1) clamping spontaneous release and 2) triggering and synchronizing evoked release. Thus, the juxtamembrane linker of syt1 plays a crucial role in exocytosis by mediating multimerization.
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12
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Barbier E, Barchiesi R, Domi A, Chanthongdee K, Domi E, Augier G, Augier E, Xu L, Adermark L, Heilig M. Downregulation of Synaptotagmin 1 in the Prelimbic Cortex Drives Alcohol-Associated Behaviors in Rats. Biol Psychiatry 2021; 89:398-406. [PMID: 33160605 DOI: 10.1016/j.biopsych.2020.08.027] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 08/17/2020] [Accepted: 08/25/2020] [Indexed: 01/18/2023]
Abstract
BACKGROUND Alcohol addiction is characterized by persistent neuroadaptations in brain structures involved in motivation, emotion, and decision making, including the medial prefrontal cortex, the nucleus accumbens, and the amygdala. We previously reported that induction of alcohol dependence was associated with long-term changes in the expression of genes involved in neurotransmitter release. Specifically, Syt1, which plays a key role in neurotransmitter release and neuronal functions, was downregulated. Here, we therefore examined the role of Syt1 in alcohol-associated behaviors in rats. METHODS We evaluated the effect of Syt1 downregulation using an adeno-associated virus (AAV) containing a short hairpin RNA against Syt1. Cre-dependent Syt1 was also used in combination with an rAAV2 retro-Cre virus to assess circuit-specific effects of Syt1 knockdown (KD). RESULTS Alcohol-induced downregulation of Syt1 is specific to the prelimbic cortex (PL), and KD of Syt1 in the PL resulted in escalated alcohol consumption, increased motivation to consume alcohol, and increased alcohol drinking despite negative consequences ("compulsivity"). Syt1 KD in the PL altered the excitation/inhibition balance in the basolateral amygdala, while the nucleus accumbens core was unaffected. Accordingly, a projection-specific Syt1 KD in the PL-basolateral amygdala projection was sufficient to increase compulsive alcohol drinking, while a KD of Syt1 restricted to PL-nucleus accumbens core projecting neurons had no effect on tested alcohol-related behaviors. CONCLUSIONS Together, these data suggest that dysregulation of Syt1 is an important mechanism in long-term neuroadaptations observed after a history of alcohol dependence, and that Syt1 regulates alcohol-related behaviors in part by affecting a PL-basolateral amygdala brain circuit.
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Affiliation(s)
- Estelle Barbier
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden.
| | - Riccardo Barchiesi
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Ana Domi
- Addiction Biology Unit, Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Kanat Chanthongdee
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden; Department of Physiology, Faculty of Medicine Siraj Hospital, Mahidol University, Bangkok, Thailand
| | - Esi Domi
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Gaelle Augier
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Eric Augier
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Li Xu
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden; Psychosomatic Medicine Center, Sichuan Academy of Medical Sciences, Sichuan Provincial People's Hospital, Chengdu, China
| | - Louise Adermark
- Addiction Biology Unit, Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Markus Heilig
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
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Huson V, Regehr WG. Diverse roles of Synaptotagmin-7 in regulating vesicle fusion. Curr Opin Neurobiol 2020; 63:42-52. [PMID: 32278209 DOI: 10.1016/j.conb.2020.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 02/12/2020] [Accepted: 02/13/2020] [Indexed: 11/18/2022]
Abstract
Synaptotagmin 7 (Syt7) is a multifunctional calcium sensor expressed throughout the body. Its high calcium affinity makes it well suited to act in processes triggered by modest calcium increases within cells. In synaptic transmission, Syt7 has been shown to mediate asynchronous neurotransmitter release, facilitation, and vesicle replenishment. In this review we provide an update on recent developments, and the newly emerging roles of Syt7 in frequency invariant synaptic transmission and in suppressing spontaneous release. Additionally, we discuss Syt7's regulation of membrane fusion in non-neuronal cells, and its involvement in disease. How such diversity of functions is regulated remains an open question. We discuss several potential factors including temperature, presynaptic calcium signals, the localization of Syt7, and its interaction with other Syt isoforms.
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Protein Kinase C and Calmodulin Serve As Calcium Sensors for Calcium-Stimulated Endocytosis at Synapses. J Neurosci 2019; 39:9478-9490. [PMID: 31628181 DOI: 10.1523/jneurosci.0182-19.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Revised: 08/27/2019] [Accepted: 10/07/2019] [Indexed: 02/04/2023] Open
Abstract
Calcium influx triggers and facilitates endocytosis, which recycles vesicles and thus sustains synaptic transmission. Despite decades of studies, the underlying calcium sensor remained not well understood. Here, we examined two calcium binding proteins, protein kinase C (PKC) and calmodulin. Whether PKC is involved in endocytosis was unclear; whether calmodulin acts as a calcium sensor for endocytosis was neither clear, although calmodulin involvement in endocytosis had been suggested. We generated PKC (α or β-isoform) and calmodulin (calmodulin 2 gene) knock-out mice of either sex and measured endocytosis with capacitance measurements, pHluorin imaging and electron microscopy. We found that these knock-outs inhibited slow (∼10-30 s) and rapid (<∼3 s) endocytosis at large calyx-type calyces, and inhibited slow endocytosis and bulk endocytosis (forming large endosome-like structures) at small conventional hippocampal synapses, suggesting the involvement of PKC and calmodulin in three most common forms of endocytosis-the slow, rapid and bulk endocytosis. Inhibition of slow endocytosis in PKC or calmodulin 2 knock-out hippocampal synapses was rescued by overexpressing wild-type PKC or calmodulin, but not calcium-binding-deficient PKC or calmodulin mutant, respectively, suggesting that calcium stimulates endocytosis by binding with its calcium sensor PKC and calmodulin. PKC and calmodulin 2 knock-out inhibited calcium-dependent vesicle mobilization to the readily releasable pool, suggesting that PKC and calmodulin may mediate calcium-dependent facilitation of vesicle mobilization. These findings shed light on the molecular signaling link among calcium, endocytosis and vesicle mobilization that are crucial in maintaining synaptic transmission and neuronal network activity.SIGNIFICANCE STATEMENT Vesicle fusion releases neurotransmitters to mediate synaptic transmission. To sustain synaptic transmission, fused vesicles must be retrieved via endocytosis. Accumulating evidence suggests that calcium influx triggers synaptic vesicle endocytosis. However, how calcium triggers endocytosis is not well understood. Using genetic tools together with capacitance measurements, optical imaging and electron microscopy, we identified two calcium sensors, including protein kinase C (α and β isoforms) and calmodulin, for the most commonly observed forms of endocytosis: slow, rapid, and bulk. We also found that these two proteins are involved in calcium-dependent vesicle mobilization to the readily releasable pool. These results provide the molecular signaling link among calcium, endocytosis, and vesicle mobilization that are essential in sustaining synaptic transmission and neuronal network activity.
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15
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Synaptotagmin-1 enables frequency coding by suppressing asynchronous release in a temperature dependent manner. Sci Rep 2019; 9:11341. [PMID: 31383906 PMCID: PMC6683208 DOI: 10.1038/s41598-019-47487-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 07/17/2019] [Indexed: 01/08/2023] Open
Abstract
To support frequency-coded information transfer, mammalian synapses tightly synchronize neurotransmitter release to action potentials (APs). However, release desynchronizes during AP trains, especially at room temperature. Here we show that suppression of asynchronous release by Synaptotagmin-1 (Syt1), but not release triggering, is highly temperature sensitive, and enhances synchronous release during high-frequency stimulation. In Syt1-deficient synapses, asynchronous release increased with temperature, opposite to wildtype synapses. Mutations in Syt1 C2B-domain polybasic stretch (Syt1 K326Q,K327Q,K331Q) did not affect synchronization during sustained activity, while the previously observed reduced synchronous response to a single AP was confirmed. However, an inflexible linker between the C2-domains (Syt1 9Pro) reduced suppression, without affecting synchronous release upon a single AP. Syt1 9Pro expressing synapses showed impaired synchronization during AP trains, which was rescued by buffering global Ca2+ to prevent asynchronous release. Hence, frequency coding relies on Syt1's temperature sensitive suppression of asynchronous release, an aspect distinct from its known vesicle recruitment and triggering functions.
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16
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Wrackmeyer U, Kaldrack J, Jüttner R, Pannasch U, Gimber N, Freiberg F, Purfürst B, Kainmueller D, Schmitz D, Haucke V, Rathjen FG, Gotthardt M. The cell adhesion protein CAR is a negative regulator of synaptic transmission. Sci Rep 2019; 9:6768. [PMID: 31043663 PMCID: PMC6494904 DOI: 10.1038/s41598-019-43150-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 04/17/2019] [Indexed: 11/09/2022] Open
Abstract
The Coxsackievirus and adenovirus receptor (CAR) is essential for normal electrical conductance in the heart, but its role in the postnatal brain is largely unknown. Using brain specific CAR knockout mice (KO), we discovered an unexpected role of CAR in neuronal communication. This includes increased basic synaptic transmission at hippocampal Schaffer collaterals, resistance to fatigue, and enhanced long-term potentiation. Spontaneous neurotransmitter release and speed of endocytosis are increased in KOs, accompanied by increased expression of the exocytosis associated calcium sensor synaptotagmin 2. Using proximity proteomics and binding studies, we link CAR to the exocytosis machinery as it associates with syntenin and synaptobrevin/VAMP2 at the synapse. Increased synaptic function does not cause adverse effects in KO mice, as behavior and learning are unaffected. Thus, unlike the connexin-dependent suppression of atrioventricular conduction in the cardiac knockout, communication in the CAR deficient brain is improved, suggesting a role for CAR in presynaptic processes.
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Affiliation(s)
- Uta Wrackmeyer
- Neuromuscular and Cardiovascular Cell Biology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - Joanna Kaldrack
- Neuromuscular and Cardiovascular Cell Biology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - René Jüttner
- Neuromuscular and Cardiovascular Cell Biology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany.,Developmental Neurobiology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - Ulrike Pannasch
- Neuroscience Research Center, Cluster of Excellence NeuroCure, Charité, 10117, Berlin, Germany
| | - Niclas Gimber
- Department of Molecular Pharmacology and Cell Biology, Leibniz Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Fabian Freiberg
- Neuromuscular and Cardiovascular Cell Biology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - Bettina Purfürst
- Core Facility Electron Microscopy, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - Dagmar Kainmueller
- Biomedical Image Analysis, Max Delbrück Center for Molecular Medicine and Berlin Institute of Health, 13125, Berlin, Germany
| | - Dietmar Schmitz
- Neuroscience Research Center, Cluster of Excellence NeuroCure, Charité, 10117, Berlin, Germany
| | - Volker Haucke
- Department of Molecular Pharmacology and Cell Biology, Leibniz Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Fritz G Rathjen
- Developmental Neurobiology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany
| | - Michael Gotthardt
- Neuromuscular and Cardiovascular Cell Biology, Max Delbrück Center for Molecular Medicine, 13125, Berlin, Germany.
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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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Lou X. Sensing Exocytosis and Triggering Endocytosis at Synapses: Synaptic Vesicle Exocytosis-Endocytosis Coupling. Front Cell Neurosci 2018; 12:66. [PMID: 29593500 PMCID: PMC5861208 DOI: 10.3389/fncel.2018.00066] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 02/26/2018] [Indexed: 12/29/2022] Open
Abstract
The intact synaptic structure is critical for information processing in neural circuits. During synaptic transmission, rapid vesicle exocytosis increases the size of never terminals and endocytosis counteracts the increase. Accumulating evidence suggests that SV exocytosis and endocytosis are tightly connected in time and space during SV recycling, and this process is essential for synaptic function and structural stability. Research in the past has illustrated the molecular details of synaptic vesicle (SV) exocytosis and endocytosis; however, the mechanisms that timely connect these two fundamental events are poorly understood at central synapses. Here we discuss recent progress in SV recycling and summarize several emerging mechanisms by which synapses can “sense” the occurrence of exocytosis and timely initiate compensatory endocytosis. They include Ca2+ sensing, SV proteins sensing, and local membrane stress sensing. In addition, the spatial organization of endocytic zones adjacent to active zones provides a structural basis for efficient coupling between SV exocytosis and endocytosis. Through linking different endocytosis pathways with SV fusion, these mechanisms ensure necessary plasticity and robustness of nerve terminals to meet diverse physiological needs.
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Affiliation(s)
- Xuelin Lou
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI, United States
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19
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Maritzen T, Haucke V. Coupling of exocytosis and endocytosis at the presynaptic active zone. Neurosci Res 2018; 127:45-52. [DOI: 10.1016/j.neures.2017.09.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 07/13/2017] [Accepted: 08/25/2017] [Indexed: 01/08/2023]
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20
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Tejero R, Lopez-Manzaneda M, Arumugam S, Tabares L. Synaptotagmin-2, and -1, linked to neurotransmission impairment and vulnerability in Spinal Muscular Atrophy. Hum Mol Genet 2018; 25:4703-4716. [PMID: 28173138 DOI: 10.1093/hmg/ddw297] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 08/22/2016] [Accepted: 08/23/2016] [Indexed: 01/19/2023] Open
Abstract
Spinal muscular atrophy (SMA) is the most frequent genetic cause of infant mortality. The disease is characterized by progressive muscle weakness and paralysis of axial and proximal limb muscles. It is caused by homozygous loss or mutation of the SMN1 gene, which codes for the Survival Motor Neuron (SMN) protein. In mouse models of the disease, neurotransmitter release is greatly impaired, but the molecular mechanisms of the synaptic dysfunction and the basis of the selective muscle vulnerability are unknown. In the present study, we investigated these open questions by comparing the molecular and functional properties of nerve terminals in severely and mildly affected muscles in the SMNΔ7 mouse model. We discovered that synaptotagmin-1 (Syt1) was developmentally downregulated in nerve terminals of highly affected muscles but not in low vulnerable muscles. Additionally, the expression levels of synaptotagmin-2 (Syt2), and its interacting protein, synaptic vesicle protein 2 (SV2) B, were reduced in proportion to the degree of muscle vulnerability while other synaptic proteins, such as syntaxin-1B (Stx1B) and synaptotagmin-7 (Syt7), were not affected. Consistently with the extremely low levels of both Syt-isoforms, and SV2B, in most affected neuromuscular synapses, the functional analysis of neurotransmission revealed highly reduced evoked release, altered short-term plasticity, low release probability, and inability to modulate normally the number of functional release sites. Together, we propose that the strong reduction of Syt2 and SV2B are key factors of the functional synaptic alteration and that the physiological downregulation of Syt1 plays a determinant role in muscle vulnerability in SMA.
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Affiliation(s)
- Rocío Tejero
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, Avda. Sánchez Pizjuán, 4. 41009 Seville, Spain
| | - Mario Lopez-Manzaneda
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, Avda. Sánchez Pizjuán, 4. 41009 Seville, Spain
| | - Saravanan Arumugam
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, Avda. Sánchez Pizjuán, 4. 41009 Seville, Spain
| | - Lucía Tabares
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, Avda. Sánchez Pizjuán, 4. 41009 Seville, Spain
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21
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Mori Y, Takamori S. Molecular Signatures Underlying Synaptic Vesicle Cargo Retrieval. Front Cell Neurosci 2018; 11:422. [PMID: 29379416 PMCID: PMC5770824 DOI: 10.3389/fncel.2017.00422] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Accepted: 12/15/2017] [Indexed: 12/31/2022] Open
Abstract
Efficient retrieval of the synaptic vesicle (SV) membrane from the presynaptic plasma membrane, a process called endocytosis, is crucial for the fidelity of neurotransmission, particularly during sustained neural activity. Although multiple modes of endocytosis have been identified, it is clear that the efficient retrieval of the major SV cargos into newly formed SVs during any of these modes is fundamental for synaptic transmission. It is currently believed that SVs are eventually reformed via a clathrin-dependent pathway. Various adaptor proteins recognize SV cargos and link them to clathrin, ensuring the efficient retrieval of the cargos into newly formed SVs. Here, we summarize our current knowledge of the molecular signatures within individual SV cargos that underlie efficient retrieval into SV membranes, as well as discuss possible contributions of the mechanisms under physiological conditions.
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Affiliation(s)
- Yasunori Mori
- Laboratory of Neural Membrane Biology, Graduate School of Brain Science, Doshisha University, Kyoto, Japan
| | - Shigeo Takamori
- Laboratory of Neural Membrane Biology, Graduate School of Brain Science, Doshisha University, Kyoto, Japan
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22
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Kaempf N, Maritzen T. Safeguards of Neurotransmission: Endocytic Adaptors as Regulators of Synaptic Vesicle Composition and Function. Front Cell Neurosci 2017; 11:320. [PMID: 29085282 PMCID: PMC5649181 DOI: 10.3389/fncel.2017.00320] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 09/26/2017] [Indexed: 11/13/2022] Open
Abstract
Communication between neurons relies on neurotransmitters which are released from synaptic vesicles (SVs) upon Ca2+ stimuli. To efficiently load neurotransmitters, sense the rise in intracellular Ca2+ and fuse with the presynaptic membrane, SVs need to be equipped with a stringently controlled set of transmembrane proteins. In fact, changes in SV protein composition quickly compromise neurotransmission and most prominently give rise to epileptic seizures. During exocytosis SVs fully collapse into the presynaptic membrane and consequently have to be replenished to sustain neurotransmission. Therefore, surface-stranded SV proteins have to be efficiently retrieved post-fusion to be used for the generation of a new set of fully functional SVs, a process in which dedicated endocytic sorting adaptors play a crucial role. The question of how the precise reformation of SVs is achieved is intimately linked to how SV membranes are retrieved. For a long time both processes were believed to be two sides of the same coin since Clathrin-mediated endocytosis (CME), the proposed predominant SV recycling mode, will jointly retrieve SV membranes and proteins. However, with the recent proposal of Clathrin-independent SV recycling pathways SV membrane retrieval and SV reformation turn into separable events. This review highlights the progress made in unraveling the molecular mechanisms mediating the high-fidelity retrieval of SV proteins and discusses how the gathered knowledge about SV protein recycling fits in with the new notions of SV membrane endocytosis.
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Affiliation(s)
- Natalie Kaempf
- Molecular Physiology and Cell Biology Section, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Tanja Maritzen
- Molecular Physiology and Cell Biology Section, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
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Wang YL, Zhang CX. Putting a brake on synaptic vesicle endocytosis. Cell Mol Life Sci 2017; 74:2917-2927. [PMID: 28361181 PMCID: PMC11107501 DOI: 10.1007/s00018-017-2506-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 02/14/2017] [Accepted: 03/14/2017] [Indexed: 01/16/2023]
Abstract
In chemical synapses, action potentials evoke synaptic vesicle fusion with the presynaptic membrane at the active zone to release neurotransmitter. Synaptic vesicle endocytosis (SVE) then follows exocytosis to recapture vesicle proteins and lipid components for recycling and the maintenance of membrane homeostasis. Therefore, SVE plays an essential role during neurotransmission and is one of the most precisely regulated biological processes. Four modes of SVE have been characterized and both positive and negative regulators have been identified. However, our understanding of SVE regulation remains unclear, especially the identity of negative regulators and their mechanisms of action. Here, we review the current knowledge of proteins that function as inhibitors of SVE and their modes of action in different forms of endocytosis. We also propose possible physiological roles of such negative regulation. We believe that a better understanding of SVE regulation, especially the inhibitory mechanisms, will shed light on neurotransmission in health and disease.
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Affiliation(s)
- Ya-Long Wang
- Center of Parkinson's Disease, Beijing Institute for Brain Disorders, Capital Medical University, Key Laboratory for the Neurodegenerative Disorders of the Chinese Ministry of Education, Beijing, China
| | - Claire Xi Zhang
- Center of Parkinson's Disease, Beijing Institute for Brain Disorders, Capital Medical University, Key Laboratory for the Neurodegenerative Disorders of the Chinese Ministry of Education, Beijing, China.
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Li YC, Kavalali ET. Synaptic Vesicle-Recycling Machinery Components as Potential Therapeutic Targets. Pharmacol Rev 2017; 69:141-160. [PMID: 28265000 DOI: 10.1124/pr.116.013342] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Presynaptic nerve terminals are highly specialized vesicle-trafficking machines. Neurotransmitter release from these terminals is sustained by constant local recycling of synaptic vesicles independent from the neuronal cell body. This independence places significant constraints on maintenance of synaptic protein complexes and scaffolds. Key events during the synaptic vesicle cycle-such as exocytosis and endocytosis-require formation and disassembly of protein complexes. This extremely dynamic environment poses unique challenges for proteostasis at synaptic terminals. Therefore, it is not surprising that subtle alterations in synaptic vesicle cycle-associated proteins directly or indirectly contribute to pathophysiology seen in several neurologic and psychiatric diseases. In contrast to the increasing number of examples in which presynaptic dysfunction causes neurologic symptoms or cognitive deficits associated with multiple brain disorders, synaptic vesicle-recycling machinery remains an underexplored drug target. In addition, irrespective of the involvement of presynaptic function in the disease process, presynaptic machinery may also prove to be a viable therapeutic target because subtle alterations in the neurotransmitter release may counter disease mechanisms, correct, or compensate for synaptic communication deficits without the need to interfere with postsynaptic receptor signaling. In this article, we will overview critical properties of presynaptic release machinery to help elucidate novel presynaptic avenues for the development of therapeutic strategies against neurologic and neuropsychiatric disorders.
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Affiliation(s)
- Ying C Li
- Departments of Neuroscience (Y.C.L., E.T.K.) and Physiology (E.T.K.), University of Texas Southwestern Medical Center, Dallas, Texas
| | - Ege T Kavalali
- Departments of Neuroscience (Y.C.L., E.T.K.) and Physiology (E.T.K.), University of Texas Southwestern Medical Center, Dallas, Texas
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Yao CK, Liu YT, Lee IC, Wang YT, Wu PY. A Ca2+ channel differentially regulates Clathrin-mediated and activity-dependent bulk endocytosis. PLoS Biol 2017; 15:e2000931. [PMID: 28414717 PMCID: PMC5393565 DOI: 10.1371/journal.pbio.2000931] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 03/21/2017] [Indexed: 11/19/2022] Open
Abstract
Clathrin-mediated endocytosis (CME) and activity-dependent bulk endocytosis (ADBE) are two predominant forms of synaptic vesicle (SV) endocytosis, elicited by moderate and strong stimuli, respectively. They are tightly coupled with exocytosis for sustained neurotransmission. However, the underlying mechanisms are ill defined. We previously reported that the Flower (Fwe) Ca2+ channel present in SVs is incorporated into the periactive zone upon SV fusion, where it triggers CME, thus coupling exocytosis to CME. Here, we show that Fwe also promotes ADBE. Intriguingly, the effects of Fwe on CME and ADBE depend on the strength of the stimulus. Upon mild stimulation, Fwe controls CME independently of Ca2+ channeling. However, upon strong stimulation, Fwe triggers a Ca2+ influx that initiates ADBE. Moreover, knockout of rodent fwe in cultured rat hippocampal neurons impairs but does not completely abolish CME, similar to the loss of Drosophila fwe at the neuromuscular junction, suggesting that Fwe plays a regulatory role in regulating CME across species. In addition, the function of Fwe in ADBE is conserved at mammalian central synapses. Hence, Fwe exerts different effects in response to different stimulus strengths to control two major modes of endocytosis.
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Affiliation(s)
- Chi-Kuang Yao
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
- Neuroscience Program in Academia Sinica, Academia Sinica, Nankang, Taipei, Taiwan
- Institute of Biochemical Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan
- * E-mail:
| | - Yu-Tzu Liu
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
| | - I-Chi Lee
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
| | - You-Tung Wang
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
| | - Ping-Yen Wu
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
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Xie Z, Long J, Liu J, Chai Z, Kang X, Wang C. Molecular Mechanisms for the Coupling of Endocytosis to Exocytosis in Neurons. Front Mol Neurosci 2017; 10:47. [PMID: 28348516 PMCID: PMC5346583 DOI: 10.3389/fnmol.2017.00047] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Accepted: 02/10/2017] [Indexed: 11/13/2022] Open
Abstract
Neuronal communication and brain function mainly depend on the fundamental biological events of neurotransmission, including the exocytosis of presynaptic vesicles (SVs) for neurotransmitter release and the subsequent endocytosis for SV retrieval. Neurotransmitters are released through the Ca2+- and SNARE-dependent fusion of SVs with the presynaptic plasma membrane. Following exocytosis, endocytosis occurs immediately to retrieve SV membrane and fusion machinery for local recycling and thus maintain the homeostasis of synaptic structure and sustained neurotransmission. Apart from the general endocytic machinery, recent studies have also revealed the involvement of SNARE proteins (synaptobrevin, SNAP25 and syntaxin), synaptophysin, Ca2+/calmodulin, and members of the synaptotagmin protein family (Syt1, Syt4, Syt7 and Syt11) in the balance and tight coupling of exo-endocytosis in neurons. Here, we provide an overview of recent progress in understanding how these neuron-specific adaptors coordinate to ensure precise and efficient endocytosis during neurotransmission.
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Affiliation(s)
- Zhenli Xie
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China; State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Jiangang Long
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China
| | - Jiankang Liu
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China
| | - Zuying Chai
- State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Xinjiang Kang
- State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China; College of Life Sciences, Liaocheng UniversityLiaocheng, China; Key Laboratory of Medical Electrophysiology, Ministry of Education of China, Collaborative Innovation Center for Prevention and Treatment of Cardiovascular Disease, Institute of Cardiovascular Research, Southwest Medical UniversityLuzhou, China
| | - Changhe Wang
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China; State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
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van Stegen B, Dagar S, Gottmann K. Release activity-dependent control of vesicle endocytosis by the synaptic adhesion molecule N-cadherin. Sci Rep 2017; 7:40865. [PMID: 28106089 PMCID: PMC5247765 DOI: 10.1038/srep40865] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 12/13/2016] [Indexed: 11/25/2022] Open
Abstract
At synapses in the mammalian brain, continuous information transfer requires the long-term maintenance of homeostatic coupling between exo- and endocytosis of synaptic vesicles. Because classical endocytosis is orders of magnitude slower than the millisecond-range exocytosis of vesicles, high frequency vesicle fusion could potentially compromise structural stability of synapses. However, the molecular mechanisms mediating the tight coupling of exo- and endocytosis are largely unknown. Here, we investigated the role of the transsynaptic adhesion molecules N-cadherin and Neuroligin1 in regulating vesicle exo- and endocytosis by using activity-induced FM4–64 staining and by using synaptophysin-pHluorin fluorescence imaging. The synaptic adhesion molecules N-cadherin and Neuroligin1 had distinct impacts on exo- and endocytosis at mature cortical synapses. Expression of Neuroligin1 enhanced vesicle release in a N-cadherin-dependent way. Most intriguingly, expression of N-cadherin enhanced both vesicle exo- and endocytosis. Further detailed analysis of N-cadherin knockout neurons revealed that the boosting of endocytosis by N-cadherin was largely dependent on preceding high levels of vesicle release activity. In summary, regulation of vesicle endocytosis was mediated at the molecular level by N-cadherin in a release activity-dependent manner. Because of its endocytosis enhancing function, N-cadherin might play an important role in the coupling of vesicle exo- and endocytosis.
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Affiliation(s)
- Bernd van Stegen
- Institute of Neuro- and Sensory Physiology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany
| | - Sushma Dagar
- Institute of Neuro- and Sensory Physiology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany
| | - Kurt Gottmann
- Institute of Neuro- and Sensory Physiology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany
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Li YC, Chanaday NL, Xu W, Kavalali ET. Synaptotagmin-1- and Synaptotagmin-7-Dependent Fusion Mechanisms Target Synaptic Vesicles to Kinetically Distinct Endocytic Pathways. Neuron 2017; 93:616-631.e3. [PMID: 28111077 DOI: 10.1016/j.neuron.2016.12.010] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 08/30/2016] [Accepted: 12/02/2016] [Indexed: 12/26/2022]
Abstract
Synaptic vesicle recycling is essential for maintaining normal synaptic function. The coupling of exocytosis and endocytosis is assumed to be Ca2+ dependent, but the exact role of Ca2+ and its key effector synaptotagmin-1 (syt1) in regulation of endocytosis is poorly understood. Here, we probed the role of syt1 in single- as well as multi-vesicle endocytic events using high-resolution optical recordings. Our experiments showed that the slowed endocytosis phenotype previously reported after syt1 loss of function can also be triggered by other manipulations that promote asynchronous release such as Sr2+ substitution and complexin loss of function. The link between asynchronous release and slowed endocytosis was due to selective targeting of fused synaptic vesicles toward slow retrieval by the asynchronous release Ca2+ sensor synaptotagmin-7. In contrast, after single synaptic vesicle fusion, syt1 acted as an essential determinant of synaptic vesicle endocytosis time course by delaying the kinetics of vesicle retrieval in response to increasing Ca2+ levels.
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Affiliation(s)
- Ying C Li
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
| | - Natali L Chanaday
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
| | - Wei Xu
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
| | - Ege T Kavalali
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA.
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29
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Okamoto Y, Lipstein N, Hua Y, Lin KH, Brose N, Sakaba T, Midorikawa M. Distinct modes of endocytotic presynaptic membrane and protein uptake at the calyx of Held terminal of rats and mice. eLife 2016; 5. [PMID: 27154627 PMCID: PMC4927297 DOI: 10.7554/elife.14643] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 05/06/2016] [Indexed: 11/15/2022] Open
Abstract
Neurotransmitter is released at synapses by fusion of synaptic vesicles with the plasma membrane. To sustain synaptic transmission, compensatory retrieval of membranes and vesicular proteins is essential. We combined capacitance measurements and pH-imaging via pH-sensitive vesicular protein marker (anti-synaptotagmin2-cypHer5E), and compared the retrieval kinetics of membranes and vesicular proteins at the calyx of Held synapse. Membrane and Syt2 were retrieved with a similar time course when slow endocytosis was elicited. When fast endocytosis was elicited, Syt2 was still retrieved together with the membrane, but endocytosed organelle re-acidification was slowed down, which provides strong evidence for two distinct endocytotic pathways. Strikingly, CaM inhibitors or the inhibition of the Ca2+-calmodulin-Munc13-1 signaling pathway only impaired the uptake of Syt2 while leaving membrane retrieval intact, indicating different recycling mechanisms for membranes and vesicle proteins. Our data identify a novel mechanism of stimulus- and Ca2+-dependent regulation of coordinated endocytosis of synaptic membranes and vesicle proteins. DOI:http://dx.doi.org/10.7554/eLife.14643.001 Nerve cells release chemicals called neurotransmitters to communicate with each other. The neurotransmitters are packaged inside membrane-encased sacs called vesicles that fuse with the cell’s membrane and release their contents into the space between the nerve cells. The vesicle membrane (which also has proteins embedded in it) can then be retrieved into the cell, and recycled to make new vesicles ready to release more neurotransmitters. Recycling vesicle components requires highly coordinated mechanisms that regulate how much membrane and vesicle protein is retrieved from the cell membrane. Researchers interested in these processes have often studied them at a part of the brainstem of mammals known as the calyx of Held. However, many of the details about how vesicle proteins are recycled remained unclear. Okamoto et al. have now measured vesicle membrane and protein retrieval at the same time and in the same cell at the calyx of Held from rats and mice. The cell surface area was also measured, and the experiments focused on a fluorescently tagged version of a vesicle protein called Synaptotagmin2 that could be tracked under a microscope. Okamoto et al. found that, in weakly active nerve cells, the vesicle membrane and Synaptotagmin2 were retrieved together at a slow rate. The process was faster in more active nerve cells, and Synaptotagmin2 was still retrieved with the membrane but it appeared to be stored first in larger sacs. This suggests that membrane and vesicle proteins may be retrieved via two distinct modes depending on the activity strength. The results of further experiments went on to suggest that vesicle membranes might be recycled in a different way from vesicle proteins. Finally, Okamoto et al. also found a signaling pathway that couples the uptake of vesicle membrane with uptake of Synaptotagmin2. Future studies could now explore how these processes work in other types of nerve cell. DOI:http://dx.doi.org/10.7554/eLife.14643.002
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Affiliation(s)
- Yuji Okamoto
- Graduate School of Brain Science, Doshisha University, Kyoto, Japan
| | - Noa Lipstein
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Yunfeng Hua
- Department of Connectomics, Max Planck Institute of Brain Research, Frankfurt, Germany.,Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Kun-Han Lin
- Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Takeshi Sakaba
- Graduate School of Brain Science, Doshisha University, Kyoto, Japan
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Linares-Clemente P, Rozas JL, Mircheski J, García-Junco-Clemente P, Martínez-López JA, Nieto-González JL, Vázquez ME, Pintado CO, Fernández-Chacón R. Different dynamin blockers interfere with distinct phases of synaptic endocytosis during stimulation in motoneurones. J Physiol 2015; 593:2867-88. [PMID: 25981717 DOI: 10.1113/jp270112] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2014] [Accepted: 04/29/2015] [Indexed: 01/05/2023] Open
Abstract
KEY POINTS Neurotransmitter release requires a tight coupling between synaptic vesicle exocytosis and endocytosis with dynamin being a key protein in that process. We used imaging techniques to examine the time course of endocytosis at mouse motor nerve terminals expressing synaptopHluorin, a genetically encoded reporter of the synaptic vesicle cycle. We separated two sequential phases of endocytosis taking place during the stimulation train: early and late endocytosis. Freshly released synaptic vesicle proteins are preferentially retrieved during the early phase, which is very sensitive to dynasore, an inhibitor of dynamin GTPase activity. Synaptic vesicle proteins pre-existing at the plasma membrane before the stimulation are preferentially retrieved during the late phase, which is very sensitive to myristyl trimethyl ammonium bromide (MitMAB), an inhibitor of the dynamin-phospholipid interaction. ABSTRACT Synaptic endocytosis is essential at nerve terminals to maintain neurotransmitter release by exocytosis. Here, at the neuromuscular junction of synaptopHluorin (spH) transgenic mice, we have used imaging to study exo- and endocytosis occurring simultaneously during nerve stimulation. We observed two endocytosis components, which occur sequentially during stimulation. The early component of endocytosis apparently internalizes spH molecules freshly exocytosed. This component was sensitive to dynasore, a blocker of dynamin 1 GTPase activity. In contrast, this early component was resistant to myristyl trimethyl ammonium bromide (MiTMAB), a competitive agent that blocks dynamin binding to phospholipid membranes. The late component of endocytosis is likely to internalize spH molecules that pre-exist at the plasma membrane before stimulation starts. This component was blocked by MiTMAB, perhaps by impairing the binding of dynamin or other key endocytic proteins to phospholipid membranes. Our study suggests the co-existence of two sequential synaptic endocytosis steps taking place during stimulation that are susceptible to pharmacological dissection: an initial step, preferentially sensitive to dynasore, that internalizes vesicular components immediately after they are released, and a MiTMAB-sensitive step that internalizes vesicular components pre-existing at the plasma membrane surface. In addition, we report that post-stimulus endocytosis also has several components with different sensitivities to dynasore and MiTMAB.
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Affiliation(s)
- Pedro Linares-Clemente
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - José L Rozas
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - Josif Mircheski
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - Pablo García-Junco-Clemente
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - José A Martínez-López
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | | | - M Eugenio Vázquez
- Departamento Química Orgánica y Centro Singular de Investigación en Química Biolóxica y Materiais Moleculares (CIQUS), Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - C Oscar Pintado
- Centro Producción y Experimentación Animal, Universidad de Sevilla, Seville, Spain
| | - Rafael Fernández-Chacón
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
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31
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McAdam RL, Varga KT, Jiang Z, Young FB, Blandford V, McPherson PS, Gong LW, Sossin WS. The juxtamembrane region of synaptotagmin 1 interacts with dynamin 1 and regulates vesicle fission during compensatory endocytosis in endocrine cells. J Cell Sci 2015; 128:2229-35. [PMID: 25964652 DOI: 10.1242/jcs.161505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Accepted: 04/30/2015] [Indexed: 12/25/2022] Open
Abstract
Synaptotagmin 1 (Syt1) is a synaptic vesicle protein that is important for the kinetics of both exocytosis and endocytosis, and is thus a candidate molecule to link these two processes. Although the tandem Ca(2+)-binding C2 domains of Syt1 have important roles in exocytosis and endocytosis, the function of the conserved juxtamembrane (jxm) linker region has yet to be determined. We now demonstrate that the jxm region of Syt1 interacts directly with the pleckstrin homology (PH) domain of the endocytic protein dynamin 1. By using cell-attached capacitance recordings with millisecond time resolution to monitor clathrin-mediated endocytosis of single vesicles in neuroendocrine chromaffin cells, we find that loss of this interaction prolongs the lifetime of the fission pore leading to defects in the dynamics of vesicle fission. These results indicate a previously undescribed interaction between two major regulatory proteins in the secretory vesicle cycle and that this interaction regulates endocytosis.
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Affiliation(s)
- Robyn L McAdam
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Kelly T Varga
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Zhongjiao Jiang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Fiona B Young
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Vanessa Blandford
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Peter S McPherson
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Liang-Wei Gong
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Wayne S Sossin
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
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32
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Mori M, Tanifuji S, Mochida S. Kinetic organization of Ca2+ signals that regulate synaptic release efficacy in sympathetic neurons. Mol Pharmacol 2014; 86:297-305. [PMID: 24981043 DOI: 10.1124/mol.114.094029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium regulation of neurotransmitter release is essential for maintenance of synaptic transmission. However, the temporal and spatial organization of Ca(2+) dynamics that regulate synaptic vesicle (SV) release efficacy in sympathetic neurons is poorly understood. Here, we investigate the N-type Ca(2+) channel-mediated kinetic structure of Ca(2+) regulation of cholinergic transmission of sympathetic neurons. We measured the effect of Ca(2+) chelation with fast 1,2-bis(2-aminophenoxy) ethane-tetraacetic acid (BAPTA) and slow ethyleneglycol-tetraacetic acid (EGTA) buffers on exocytosis, synaptic depression, and recovery of the readily releasable vesicle pool (RRP), after both single action potential (AP) and repetitive APs. Surprisingly, postsynaptic potentials peaking at ~12 milliseconds after the AP was inhibited by both rapid and slow Ca(2+) buffers suggests that, in addition to the well known fast Ca(2+) signals at the active zone (AZ), slow Ca(2+) signals at the peak of Ca(2+) entry also contribute to paired-pulse or repetitive AP responses. Following a single AP, discrete Ca(2+) transient increase regulated synaptic depression in rapid (<30-millisecond) and slow (<120-millisecond) phases. In contrast, following prolonged AP trains, synaptic depression was reduced by a slow Ca(2+) signal regulation lasting >200 milliseconds. Finally, after an AP burst, recovery of the RRP was mediated by an AP-dependent rapid Ca(2+) signal, and the expansion of releasable SV number by an AP firing activity-dependent slow Ca(2+) signal. These data indicate that local Ca(2+) signals operating near Ca(2+) sources in the AZ are organized into discrete fast and slow temporal phases that remodel exocytosis and short-term plasticity to ensure long-term stability in acetylcholine release efficacy.
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Affiliation(s)
- Michinori Mori
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
| | - Shota Tanifuji
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
| | - Sumiko Mochida
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
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33
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Wu XS, Zhang Z, Zhao WD, Wang D, Luo F, Wu LG. Calcineurin is universally involved in vesicle endocytosis at neuronal and nonneuronal secretory cells. Cell Rep 2014; 7:982-8. [PMID: 24835995 DOI: 10.1016/j.celrep.2014.04.020] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 03/05/2014] [Accepted: 04/11/2014] [Indexed: 01/28/2023] Open
Abstract
Calcium influx triggers and accelerates endocytosis in nerve terminals and nonneuronal secretory cells. Whether calcium/calmodulin-activated calcineurin, which dephosphorylates endocytic proteins, mediates this process is highly controversial for different cell types, developmental stages, and endocytic forms. Using three preparations that previously produced discrepant results (i.e., large calyx-type synapses, conventional cerebellar synapses, and neuroendocrine chromaffin cells containing large dense-core vesicles), we found that calcineurin gene knockout consistently slowed down endocytosis, regardless of cell type, developmental stage, or endocytic form (rapid or slow). In contrast, calcineurin and calmodulin blockers slowed down endocytosis at a relatively small calcium influx, but did not inhibit endocytosis at a large calcium influx, resulting in false-negative results. These results suggest that calcineurin is universally involved in endocytosis. They may also help explain the discrepancies among previous pharmacological studies. We therefore suggest that calcineurin should be included as a key player in mediating calcium-triggered and -accelerated vesicle endocytosis.
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Affiliation(s)
- Xin-Sheng Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Zhen Zhang
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Wei-Dong Zhao
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Dongsheng Wang
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Fujun Luo
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | - Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA.
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Wu LG, Hamid E, Shin W, Chiang HC. Exocytosis and endocytosis: modes, functions, and coupling mechanisms. Annu Rev Physiol 2013; 76:301-31. [PMID: 24274740 DOI: 10.1146/annurev-physiol-021113-170305] [Citation(s) in RCA: 283] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Vesicle exocytosis releases content to mediate many biological events, including synaptic transmission essential for brain functions. Following exocytosis, endocytosis is initiated to retrieve exocytosed vesicles within seconds to minutes. Decades of studies in secretory cells reveal three exocytosis modes coupled to three endocytosis modes: (a) full-collapse fusion, in which vesicles collapse into the plasma membrane, followed by classical endocytosis involving membrane invagination and vesicle reformation; (b) kiss-and-run, in which the fusion pore opens and closes; and (c) compound exocytosis, which involves exocytosis of giant vesicles formed via vesicle-vesicle fusion, followed by bulk endocytosis that retrieves giant vesicles. Here we review these exo- and endocytosis modes and their roles in regulating quantal size and synaptic strength, generating synaptic plasticity, maintaining exocytosis, and clearing release sites for vesicle replenishment. Furthermore, we highlight recent progress in understanding how vesicle endocytosis is initiated and is thus coupled to exocytosis. The emerging model is that calcium influx via voltage-dependent calcium channels at the calcium microdomain triggers endocytosis and controls endocytosis rate; calmodulin and synaptotagmin are the calcium sensors; and the exocytosis machinery, including SNARE proteins (synaptobrevin, SNAP25, and syntaxin), is needed to coinitiate endocytosis, likely to control the amount of endocytosis.
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Affiliation(s)
- Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892; ,
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35
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Puchkov D, Haucke V. Greasing the synaptic vesicle cycle by membrane lipids. Trends Cell Biol 2013; 23:493-503. [DOI: 10.1016/j.tcb.2013.05.002] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 04/30/2013] [Accepted: 05/02/2013] [Indexed: 12/18/2022]
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Armbruster M, Messa M, Ferguson SM, De Camilli P, Ryan TA. Dynamin phosphorylation controls optimization of endocytosis for brief action potential bursts. eLife 2013; 2:e00845. [PMID: 23908769 PMCID: PMC3728620 DOI: 10.7554/elife.00845] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 06/24/2013] [Indexed: 12/13/2022] Open
Abstract
Modulation of synaptic vesicle retrieval is considered to be potentially important in steady-state synaptic performance. Here we show that at physiological temperature endocytosis kinetics at hippocampal and cortical nerve terminals show a bi-phasic dependence on electrical activity. Endocytosis accelerates for the first 15–25 APs during bursts of action potential firing, after which it slows with increasing burst length creating an optimum stimulus for this kinetic parameter. We show that activity-dependent acceleration is only prominent at physiological temperature and that the mechanism of this modulation is based on the dephosphorylation of dynamin 1. Nerve terminals in which dynamin 1 and 3 have been replaced with dynamin 1 harboring dephospho- or phospho-mimetic mutations in the proline-rich domain eliminate the acceleration phase by either setting endocytosis at an accelerated state or a decelerated state, respectively. DOI:http://dx.doi.org/10.7554/eLife.00845.001 Neurons communicate with each other at specialized junctions called synapses. When signals travelling along a neuron reach the presynaptic cell, this triggers small packages (vesicles) containing neurotransmitter molecules to release their contents into the synapse, and these molecules then cross the gap and bind to receptors on the postsynaptic neuron. To release their cargo, individual vesicles fuse with the plasma membrane of the presynaptic neuron and form a ‘pore’ through which neurotransmitter molecules can leave the cell. However, to avoid running out of vesicles, the neuron must recycle and rebuild them through a process known as endocytosis. This involves recapturing the proteins that make up the synaptic vesicle and internalizing them back into the presynaptic terminal. Exactly how endocytosis is regulated has been the subject of much debate in recent years. Now, Armbruster et al. have used fluorescent markers to study the timing of endocytosis in unprecedented detail. Observations of individual synapses reveal that when a series of action potentials (spikes of electrical activity) occurs in a neuron, endocytosis accelerates during the first few action potentials, and then slows. However, this acceleration was only detectable at a physiological temperature of 37°C—markedly higher than the 30°C at which synaptic endocytosis is typically studied. The new study showed that acceleration of endocytosis depends on the phosphorylation status of dynamin, a mechano-chemical enzyme long known to be crucial for endocytosis, which helps to sever the connection between the endocytosing membrane and the surface of the cell. Phosphorylation is a common mechanism for controlling enzyme activity, and involves the addition of phosphate groups to specific amino acids by enzymes called kinases. Phosphatase enzymes reverse the process by removing the phosphate groups. Dynamin is usually phosphorylated at two specific amino acids, but when levels of calcium in the cell increase (as occurs during action potentials), a phosphatase called calcineurin dephosphorylates these sites. Using versions of dynamin that were either permanently phosphorylated or never phosphorylated, Armbruster et al. showed that a decrease in dynamin phosphorylation was required for the initial acceleration of endocytosis. This type of regulation seems to optimize the recycling of vesicles to enable neurons to respond effectively to brief bursts of stimulation. Given that dynamin phosphorylation is conserved in evolution, it is likely that regulation of synaptic endocytosis is a key mechanism for ensuring the efficient functioning of the nervous system. Future research will investigate how calcium influx mediates the later slowing of endocytosis, and help to further unravel this previously unknown regulatory process. DOI:http://dx.doi.org/10.7554/eLife.00845.002
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Affiliation(s)
- Moritz Armbruster
- Department of Biochemistry , Weill Cornell Medical College , New York , United States ; The David Rockefeller Graduate Program , Rockefeller University , New York , United States
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Genetic analysis of synaptotagmin C2 domain specificity in regulating spontaneous and evoked neurotransmitter release. J Neurosci 2013; 33:187-200. [PMID: 23283333 DOI: 10.1523/jneurosci.3214-12.2013] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Synaptic vesicle fusion mediates communication between neurons and is triggered by rapid influx of Ca(2+). The Ca(2+)-triggering step for fusion is regulated by the synaptic vesicle transmembrane protein Synaptotagmin 1 (Syt1). Syt1 contains two cytoplasmic C2 domains, termed C2A and C2B, which coordinate Ca(2+) binding. Although C2A and C2B share similar topology, binding of Ca(2+) ions to the C2B domain has been suggested as the only critical trigger for evoked vesicle release. If and how C2A domain function is coordinated with C2B remain unclear. In this study, we generated a panel of Syt1 chimeric constructs in Drosophila to delineate the unique and shared functions of each C2 domain in regulation of synaptic vesicle fusion. Expression of Syt 1 transgenes containing only individual C2 domains, or dual C2A-C2A or C2B-C2B chimeras, failed to restore Syt1 function in a syt1(-/-) null mutant background, indicating both C2A and C2B are specifically required to support fast synchronous release. Mutations that disrupted Ca(2+) binding to both C2 domains failed to rescue evoked release, but supported synaptic vesicle docking and endocytosis, indicating that these functions of Syt1 are Ca(2+)-independent. The dual C2 domain Ca(2+)-binding mutant also enhanced spontaneous fusion while dramatically increasing evoked release when coexpressed with native Syt1. Together, these data indicate that synaptic transmission can be regulated by Syt1 multimerization and that both C2 domains of Syt1 are uniquely required for modulating Ca(2+)-independent spontaneous fusion and Ca(2+)-dependent synchronous release.
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Kononenko NL, Diril MK, Puchkov D, Kintscher M, Koo SJ, Pfuhl G, Winter Y, Wienisch M, Klingauf J, Breustedt J, Schmitz D, Maritzen T, Haucke V. Compromised fidelity of endocytic synaptic vesicle protein sorting in the absence of stonin 2. Proc Natl Acad Sci U S A 2013; 110:E526-35. [PMID: 23345427 PMCID: PMC3568307 DOI: 10.1073/pnas.1218432110] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurotransmission depends on the exocytic fusion of synaptic vesicles (SVs) and their subsequent reformation either by clathrin-mediated endocytosis or budding from bulk endosomes. How synapses are able to rapidly recycle SVs to maintain SV pool size, yet preserve their compositional identity, is poorly understood. We demonstrate that deletion of the endocytic adaptor stonin 2 (Stn2) in mice compromises the fidelity of SV protein sorting, whereas the apparent speed of SV retrieval is increased. Loss of Stn2 leads to selective missorting of synaptotagmin 1 to the neuronal surface, an elevated SV pool size, and accelerated SV protein endocytosis. The latter phenotype is mimicked by overexpression of endocytosis-defective variants of synaptotagmin 1. Increased speed of SV protein retrieval in the absence of Stn2 correlates with an up-regulation of SV reformation from bulk endosomes. Our results are consistent with a model whereby Stn2 is required to preserve SV protein composition but is dispensable for maintaining the speed of SV recycling.
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Affiliation(s)
- Natalia L. Kononenko
- Department of Molecular Pharmacology and Cell Biology, Leibniz Institut für Molekulare Pharmakologie, 13125 Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Berlin, 10117 Berlin, Germany
| | - M. Kasim Diril
- Freie Universität Berlin, Institut für Chemie und Biochemie, 14195 Berlin, Germany
| | - Dmytro Puchkov
- Department of Molecular Pharmacology and Cell Biology, Leibniz Institut für Molekulare Pharmakologie, 13125 Berlin, Germany
| | - Michael Kintscher
- NeuroCure Cluster of Excellence, Charité Berlin, 10117 Berlin, Germany
| | - Seong Joo Koo
- Department of Molecular Pharmacology and Cell Biology, Leibniz Institut für Molekulare Pharmakologie, 13125 Berlin, Germany
| | - Gerit Pfuhl
- Department of Cognitive Neurobiology, Humboldt Universität zu Berlin, 10117 Berlin, Germany; and
| | - York Winter
- Department of Cognitive Neurobiology, Humboldt Universität zu Berlin, 10117 Berlin, Germany; and
| | - Martin Wienisch
- Institute for Medical Physics and Biophysics, University of Münster, 48149 Münster, Germany
| | - Jürgen Klingauf
- Institute for Medical Physics and Biophysics, University of Münster, 48149 Münster, Germany
| | - Jörg Breustedt
- NeuroCure Cluster of Excellence, Charité Berlin, 10117 Berlin, Germany
| | - Dietmar Schmitz
- NeuroCure Cluster of Excellence, Charité Berlin, 10117 Berlin, Germany
| | - Tanja Maritzen
- Department of Molecular Pharmacology and Cell Biology, Leibniz Institut für Molekulare Pharmakologie, 13125 Berlin, Germany
| | - Volker Haucke
- Department of Molecular Pharmacology and Cell Biology, Leibniz Institut für Molekulare Pharmakologie, 13125 Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Berlin, 10117 Berlin, Germany
- Freie Universität Berlin, Institut für Chemie und Biochemie, 14195 Berlin, Germany
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39
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Otoferlin: a multi-C2 domain protein essential for hearing. Trends Neurosci 2012; 35:671-80. [DOI: 10.1016/j.tins.2012.08.002] [Citation(s) in RCA: 100] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 07/25/2012] [Accepted: 08/13/2012] [Indexed: 12/21/2022]
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Abstract
Neurons can sustain high rates of synaptic transmission without exhausting their supply of synaptic vesicles. This property relies on a highly efficient local endocytic recycling of synaptic vesicle membranes, which can be reused for hundreds, possibly thousands, of exo-endocytic cycles. Morphological, physiological, molecular, and genetic studies over the last four decades have provided insight into the membrane traffic reactions that govern this recycling and its regulation. These studies have shown that synaptic vesicle endocytosis capitalizes on fundamental and general endocytic mechanisms but also involves neuron-specific adaptations of such mechanisms. Thus, investigations of these processes have advanced not only the field of synaptic transmission but also, more generally, the field of endocytosis. This article summarizes current information on synaptic vesicle endocytosis with an emphasis on the underlying molecular mechanisms and with a special focus on clathrin-mediated endocytosis, the predominant pathway of synaptic vesicle protein internalization.
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Affiliation(s)
- Yasunori Saheki
- Department of Cell Biology, Howard Hughes Medical Institute and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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41
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Greif KF, Asabere N, Lutz GJ, Gallo G. Synaptotagmin-1 promotes the formation of axonal filopodia and branches along the developing axons of forebrain neurons. Dev Neurobiol 2012; 73:27-44. [PMID: 22589224 DOI: 10.1002/dneu.22033] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2012] [Revised: 04/29/2012] [Accepted: 05/08/2012] [Indexed: 01/01/2023]
Abstract
Synaptotagmin-1 (syt1) is a Ca(2+)-binding protein that functions in regulation of synaptic vesicle exocytosis at the synapse. Syt1 is expressed in many types of neurons well before synaptogenesis begins both in vivo and in vitro. To determine if expression of syt1 has a functional role in neuronal development before synapse formation, we examined the effects of syt1 overexpression and knockdown on the growth and branching of the axons of cultured primary embryonic day 8 chicken forebrain neurons. In vivo these neurons express syt1, and most have not yet extended axons. We present evidence that syt1 plays a role in regulating axon branching, while not regulating overall axon length. To study the effects of overexpression of syt1, we used adenovirus-mediated infection to introduce a syt1-YFP construct, or control GFP construct, into neurons. Syt1 levels were reduced using RNA interference. Overexpression of syt1 increased the formation of axonal filopodia and branches. Conversely, knockdown of syt1 decreased the number of axonal filopodia and branches. Time-lapse analysis of filopodial dynamics in syt1-overexpressing cells demonstrated that elevation of syt1 levels increased both the frequency of filopodial initiation and their lifespan. Taken together these data indicate that syt1 regulates the formation of axonal filopodia and branches before engaging in its conventional functions at the synapse.
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Affiliation(s)
- Karen F Greif
- Department of Biology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, USA.
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42
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Yamashita T. Ca2+-dependent regulation of synaptic vesicle endocytosis. Neurosci Res 2012; 73:1-7. [DOI: 10.1016/j.neures.2012.02.012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 02/16/2012] [Accepted: 02/17/2012] [Indexed: 01/25/2023]
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Abstract
The role of Ca²⁺ in synaptic vesicle endocytosis remains uncertain due to the diversity in various preparations where several forms of endocytosis may contribute variably in different conditions. Although recent studies have demonstrated that Ca²⁺ is important for clathrin-mediated endocytosis (CME), the mechanistic role of Ca²⁺ in CME remains to be elucidated. By monitoring CME of single vesicles in mouse chromaffin cells with cell-attached capacitance measurements that offer millisecond time resolution, we demonstrate that the dynamics of vesicle fission during CME is Ca²⁺ dependent but becomes Ca²⁺ independent in synaptotagmin 1 (Syt1) knock-out cells. Our results thus suggest that Syt1 is necessary for the Ca²⁺ dependence of CME.
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44
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Motorneurons Require Cysteine String Protein-α to Maintain the Readily Releasable Vesicular Pool and Synaptic Vesicle Recycling. Neuron 2012; 74:151-65. [DOI: 10.1016/j.neuron.2012.02.019] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/23/2012] [Indexed: 11/22/2022]
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45
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Koch M, Holt M. Coupling exo- and endocytosis: an essential role for PIP₂ at the synapse. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1114-32. [PMID: 22387937 DOI: 10.1016/j.bbalip.2012.02.008] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Revised: 02/12/2012] [Accepted: 02/13/2012] [Indexed: 12/24/2022]
Abstract
Chemical synapses are specialist points of contact between two neurons, where information transfer takes place. Communication occurs through the release of neurotransmitter substances from small synaptic vesicles in the presynaptic terminal, which fuse with the presynaptic plasma membrane in response to neuronal stimulation. However, as neurons in the central nervous system typically only possess ~200 vesicles, high levels of release would quickly lead to a depletion in the number of vesicles, as well as leading to an increase in the area of the presynaptic plasma membrane (and possible misalignment with postsynaptic structures). Hence, synaptic vesicle fusion is tightly coupled to a local recycling of synaptic vesicles. For a long time, however, the exact molecular mechanisms coupling fusion and subsequent recycling remained unclear. Recent work now indicates a unique role for the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP(2)), acting together with the vesicular protein synaptotagmin, in coupling these two processes. In this work, we review the evidence for such a mechanism and discuss both the possible advantages and disadvantages for vesicle recycling (and hence signal transduction) in the nervous system. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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Affiliation(s)
- Marta Koch
- Laboratory of Neurogenetics, VIB Center for the Biology of Disease and K.U. Leuven Center for Human Genetics, O&N4 Herestraat 49, 3000 Leuven, Belgium
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46
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Reduced release probability prevents vesicle depletion and transmission failure at dynamin mutant synapses. Proc Natl Acad Sci U S A 2012; 109:E515-23. [PMID: 22308498 DOI: 10.1073/pnas.1121626109] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Endocytic recycling of synaptic vesicles after exocytosis is critical for nervous system function. At synapses of cultured neurons that lack the two "neuronal" dynamins, dynamin 1 and 3, smaller excitatory postsynaptic currents are observed due to an impairment of the fission reaction of endocytosis that results in an accumulation of arrested clathrin-coated pits and a greatly reduced synaptic vesicle number. Surprisingly, despite a smaller readily releasable vesicle pool and fewer docked vesicles, a strong facilitation, which correlated with lower vesicle release probability, was observed upon action potential stimulation at such synapses. Furthermore, although network activity in mutant cultures was lower, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activity was unexpectedly increased, consistent with the previous report of an enhanced state of synapsin 1 phosphorylation at CaMKII-dependent sites in such neurons. These changes were partially reversed by overnight silencing of synaptic activity with tetrodotoxin, a treatment that allows progression of arrested endocytic pits to synaptic vesicles. Facilitation was also counteracted by CaMKII inhibition. These findings reveal a mechanism aimed at preventing synaptic transmission failure due to vesicle depletion when recycling vesicle traffic is backed up by a defect in dynamin-dependent endocytosis and provide new insight into the coupling between endocytosis and exocytosis.
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47
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Uncoupling the roles of synaptotagmin I during endo- and exocytosis of synaptic vesicles. Nat Neurosci 2011; 15:243-9. [PMID: 22197832 PMCID: PMC3435110 DOI: 10.1038/nn.3013] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 11/14/2011] [Indexed: 11/29/2022]
Abstract
Synaptotagmin I (syt1) is required for normal rates of synaptic vesicle endo- and exocytosis. However, whether the kinetic defects observed during endocytosis in syt1 knock-out neurons are secondary to defective exocytosis, or whether syt1 directly regulates the rate of vesicle retrieval, remains unresolved. In order to address this question, it is necessary to dissociate these two activities. Here, we have uncoupled the function of syt1 in exo- and endocytosis by re-targeting of the protein, or via mutagenesis of its tandem C2-domains; the impact of these manipulations on exo- and endocytosis were analyzed via electrophysiology, in conjunction with optical imaging of the vesicle cycle. These experiments uncovered a direct role for syt1 in endocytosis. Surprisingly, either C2-domain of syt1 - C2A or C2B - was able to function as Ca2+-sensor for endocytosis. Hence, syt1 functions as a dual Ca2+ sensor for both endo- and exocytosis, potentially coupling these two limbs of the vesicle cycle.
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48
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Messmer K, Shen WB, Remington M, Fishman PS. Induction of neural differentiation by the transcription factor neuroD2. Int J Dev Neurosci 2011; 30:105-12. [PMID: 22197973 DOI: 10.1016/j.ijdevneu.2011.12.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 09/30/2011] [Accepted: 12/09/2011] [Indexed: 01/08/2023] Open
Abstract
Pro-neural basic helix loop helix (bHLH) transcription factors are involved in many aspects of normal neuronal development, and over-expression of genes for several of these factors has been shown to induce aspects of neuronal differentiation in cell lines and stem cells. Here we show that over-expression of NeuroD2 (ND2), Neurogenin1 and 2 leads to morphological differentiation of N18-RE-105 neuroblastoma cells and increased expression of synaptic proteins. Particularly ND2 induced neurite formation and increases in the expression of synaptic proteins such as synaptotagmin, that is not expressed normally in this cell type, as well as the redistribution of another synaptic protein, SNAP25, to a cell membrane location. Infection of human neural progenitor cells using adeno associated viral (AAV) vectors also promoted neuronal differentiation. Over-expressing cells demonstrated a significant increase in the neuron specific form of tubulin as well as increased expression of synaptotagmin. Genetic modification of neural progenitor cell with bHLH factors such as ND2 may be a viable strategy to enhance differentiation of these cells into replacement neurons for human disease.
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Affiliation(s)
- Kirsten Messmer
- Department of Pharmacology and Experimental Therapeutics, University of Maryland, School of Medicine, Baltimore, MD 21201, USA
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49
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Vrljic M, Strop P, Hill RC, Hansen KC, Chu S, Brunger AT. Post-translational modifications and lipid binding profile of insect cell-expressed full-length mammalian synaptotagmin 1. Biochemistry 2011; 50:9998-10012. [PMID: 21928778 PMCID: PMC3217305 DOI: 10.1021/bi200998y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Synaptotagmin 1 (Syt1) is a Ca(2+) sensor for SNARE-mediated, Ca(2+)-triggered synaptic vesicle fusion in neurons. It is composed of luminal, transmembrane, linker, and two Ca(2+)-binding (C2) domains. Here we describe expression and purification of full-length mammalian Syt1 in insect cells along with an extensive biochemical characterization of the purified protein. The expressed and purified protein is properly folded and has increased α-helical content compared to the C2AB fragment alone. Post-translational modifications of Syt1 were analyzed by mass spectrometry, revealing the same modifications of Syt1 that were previously described for Syt1 purified from brain extract or mammalian cell lines, along with a novel modification of Syt1, tyrosine nitration. A lipid binding screen with both full-length Syt1 and the C2AB fragments of Syt1 and Syt3 isoforms revealed new Syt1-lipid interactions. These results suggest a conserved lipid binding mechanism in which Ca(2+)-independent interactions are mediated via a lysine rich region of the C2B domain while Ca(2+)-dependent interactions are mediated via the Ca(2+)-binding loops.
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Affiliation(s)
- Marija Vrljic
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305-5432, USA
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50
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Kwon SE, Chapman ER. Synaptophysin regulates the kinetics of synaptic vesicle endocytosis in central neurons. Neuron 2011; 70:847-54. [PMID: 21658579 DOI: 10.1016/j.neuron.2011.04.001] [Citation(s) in RCA: 320] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2011] [Indexed: 01/27/2023]
Abstract
Despite being the most abundant synaptic vesicle membrane protein, the function of synaptophysin remains enigmatic. For example, synaptic transmission was reported to be completely normal in synaptophysin knockout mice; however, direct experiments to monitor the synaptic vesicle cycle have not been carried out. Here, using optical imaging and electrophysiological experiments, we demonstrate that synaptophysin is required for kinetically efficient endocytosis of synaptic vesicles in cultured hippocampal neurons. Truncation analysis revealed that distinct structural elements of synaptophysin differentially regulate vesicle retrieval during and after stimulation. Thus, synaptophysin regulates at least two phases of endocytosis to ensure vesicle availability during and after sustained neuronal activity.
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Affiliation(s)
- Sung E Kwon
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, WI 53706, USA
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