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Afuwape OAT, Chanaday NL, Kasap M, Monteggia LM, Kavalali ET. Persistence of quantal synaptic vesicle recycling in virtual absence of dynamins. J Physiol 2024. [PMID: 39141823 DOI: 10.1113/jp286711] [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: 04/08/2024] [Accepted: 07/23/2024] [Indexed: 08/16/2024] Open
Abstract
Dynamins are GTPases required for pinching vesicles off the plasma membrane once a critical curvature is reached during endocytosis. Here, we probed dynamin function in central synapses by depleting all three dynamin isoforms in postnatal hippocampal neurons down to negligible levels. We found a decrease in the propensity of evoked neurotransmission as well as a reduction in synaptic vesicle numbers. Recycling of synaptic vesicles during spontaneous or low levels of evoked activity were largely impervious to dynamin depletion, while retrieval of synaptic vesicle components at higher levels of activity was partially arrested. These results suggest the existence of balancing dynamin-independent mechanisms for synaptic vesicle recycling at central synapses. Classical dynamin-dependent mechanisms are not essential for retrieval of synaptic vesicle proteins after quantal single synaptic vesicle fusion, but they become more relevant for membrane retrieval during intense, sustained neuronal activity. KEY POINTS: Loss of dynamin 2 does not impair synaptic transmission. Loss of all three dynamin isoforms mostly affects evoked neurotransmission. Excitatory synapse function is more susceptible to dynamin loss. Spontaneous neurotransmission is only mildly affected by loss of dynamins. Single synaptic vesicle endocytosis is largely dynamin independent.
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Affiliation(s)
- Olusoji A T Afuwape
- Department of Neurosurgery, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
| | - Natali L Chanaday
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
| | - Merve Kasap
- U.S. Food and Drug Administration, The Center for Drug Evaluation and Research (CDER), Silver Spring, Maryland, USA
| | - Lisa M Monteggia
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, Tennessee, USA
| | - Ege T Kavalali
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, Tennessee, USA
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2
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Zhang M, Augustine GJ. Synapsins and the Synaptic Vesicle Reserve Pool: Floats or Anchors? Cells 2021; 10:cells10030658. [PMID: 33809712 PMCID: PMC8002314 DOI: 10.3390/cells10030658] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 03/08/2021] [Accepted: 03/11/2021] [Indexed: 11/24/2022] Open
Abstract
In presynaptic terminals, synaptic vesicles (SVs) are found in a discrete cluster that includes a reserve pool that is mobilized during synaptic activity. Synapsins serve as a key protein for maintaining SVs within this reserve pool, but the mechanism that allows synapsins to do this is unclear. This mechanism is likely to involve synapsins either cross-linking SVs, thereby anchoring SVs to each other, or creating a liquid phase that allows SVs to float within a synapsin droplet. Here, we summarize what is known about the role of synapsins in clustering of SVs and evaluate experimental evidence supporting these two models.
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Arriagada-Diaz J, Prado-Vega L, Cárdenas Díaz AM, Ardiles AO, Gonzalez-Jamett AM. Dynamin Superfamily at Pre- and Postsynapses: Master Regulators of Synaptic Transmission and Plasticity in Health and Disease. Neuroscientist 2020; 28:41-58. [PMID: 33300419 DOI: 10.1177/1073858420974313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Dynamin superfamily proteins (DSPs) comprise a large group of GTP-ases that orchestrate membrane fusion and fission, and cytoskeleton remodeling in different cell-types. At the central nervous system, they regulate synaptic vesicle recycling and signaling-receptor turnover, allowing the maintenance of synaptic transmission. In the presynapses, these GTP-ases control the recycling of synaptic vesicles influencing the size of the ready-releasable pool and the release of neurotransmitters from nerve terminals, whereas in the postsynapses, they are involved in AMPA-receptor trafficking to and from postsynaptic densities, supporting excitatory synaptic plasticity, and consequently learning and memory formation. In agreement with these relevant roles, an important number of neurological disorders are associated with mutations and/or dysfunction of these GTP-ases. Along the present review we discuss the importance of DSPs at synapses and their implication in different neuropathological contexts.
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Affiliation(s)
- Jorge Arriagada-Diaz
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.,Programa de Magister en Ciencias, mención Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Lorena Prado-Vega
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.,Programa de Magister en Ciencias, mención Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Ana M Cárdenas Díaz
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Alvaro O Ardiles
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.,Centro de Neurología Traslacional, Facultad de Medicina, Universidad de Valparaíso, Valparaíso, Chile.,Centro Interdisciplinario de Estudios en Salud, Facultad de Medicina, Universidad de Valparaíso, Viña del Mar, Chile
| | - Arlek M Gonzalez-Jamett
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
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4
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Absence of Sac2/INPP5F enhances the phenotype of a Parkinson's disease mutation of synaptojanin 1. Proc Natl Acad Sci U S A 2020; 117:12428-12434. [PMID: 32424101 PMCID: PMC7275725 DOI: 10.1073/pnas.2004335117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Extensive genetic studies have identified numerous genes whose mutations results on Parkinson’s disease (PD), including synaptojanin 1 (SJ1/Park20), a nerve terminal enriched protein that includes an inositol 4-phosphatase domain (Sac domain). In addition, many PD candidate genes have been identified by genome-wide association studies, but for most of these genes, the link to PD remains hypothetical. One such gene is Sac2/INPP5F, which, interestingly, also includes an inositol 4-phosphatase domain. While Sac2KO mice do not show obvious defects, we show a striking synthetic effect in mice of the KO of Sac2 and the Sac domain mutation of SJ1 found in PD patients. These findings support a synergistic role of SJ1 and Sac2 on a PI4P pool whose dysfunction results in PD. Numerous genes whose mutations cause, or increase the risk of, Parkinson’s disease (PD) have been identified. An inactivating mutation (R258Q) in the Sac inositol phosphatase domain of synaptojanin 1 (SJ1/PARK20), a phosphoinositide phosphatase implicated in synaptic vesicle recycling, results in PD. The gene encoding Sac2/INPP5F, another Sac domain-containing protein, is located within a PD risk locus identified by genome-wide association studies. Knock-In mice carrying the SJ1 patient mutation (SJ1RQKI) exhibit PD features, while Sac2 knockout mice (Sac2KO) do not have obvious neurologic defects. We report a “synthetic” effect of the SJ1 mutation and the KO of Sac2 in mice. Most mice with both mutations died perinatally. The occasional survivors had stunted growth, died within 3 wk, and showed abnormalities of striatal dopaminergic nerve terminals at an earlier stage than SJ1RQKI mice. The abnormal accumulation of endocytic factors observed at synapses of cultured SJ1RQKI neurons was more severe in double-mutant neurons. Our results suggest that SJ1 and Sac2 have partially overlapping functions and are consistent with a potential role of Sac2 as a PD risk gene.
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Hsc70 Ameliorates the Vesicle Recycling Defects Caused by Excess α-Synuclein at Synapses. eNeuro 2020; 7:ENEURO.0448-19.2020. [PMID: 31941659 PMCID: PMC7031854 DOI: 10.1523/eneuro.0448-19.2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 12/17/2019] [Accepted: 01/03/2020] [Indexed: 02/06/2023] Open
Abstract
α-Synuclein overexpression and aggregation are linked to Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and several other neurodegenerative disorders. In addition to effects in the cell body, α-synuclein accumulation occurs at presynapses where the protein is normally localized. While it is generally agreed that excess α-synuclein impairs synaptic vesicle trafficking, the underlying mechanisms are unknown. α-Synuclein overexpression and aggregation are linked to Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and several other neurodegenerative disorders. In addition to effects in the cell body, α-synuclein accumulation occurs at presynapses where the protein is normally localized. While it is generally agreed that excess α-synuclein impairs synaptic vesicle trafficking, the underlying mechanisms are unknown. We show here that acute introduction of excess human α-synuclein at a classic vertebrate synapse, the lamprey reticulospinal (RS) synapse, selectively impaired the uncoating of clathrin-coated vesicles (CCVs) during synaptic vesicle recycling, leading to an increase in endocytic intermediates and a severe depletion of synaptic vesicles. Furthermore, human α-synuclein and lamprey γ-synuclein both interact in vitro with Hsc70, the chaperone protein that uncoats CCVs at synapses. After introducing excess α-synuclein, Hsc70 availability was reduced at stimulated synapses, suggesting Hsc70 sequestration as a possible mechanism underlying the synaptic vesicle trafficking defects. In support of this hypothesis, increasing the levels of exogenous Hsc70 along with α-synuclein ameliorated the CCV uncoating and vesicle recycling defects. These experiments identify a reduction in Hsc70 availability at synapses, and consequently its function, as the mechanism by which α-synuclein induces synaptic vesicle recycling defects. To our knowledge, this is the first report of a viable chaperone-based strategy for reversing the synaptic vesicle trafficking defects associated with excess α-synuclein, which may be of value for improving synaptic function in PD and other synuclein-linked diseases.
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Dalmau J, Geis C, Graus F. Autoantibodies to Synaptic Receptors and Neuronal Cell Surface Proteins in Autoimmune Diseases of the Central Nervous System. Physiol Rev 2017; 97:839-887. [PMID: 28298428 PMCID: PMC5539405 DOI: 10.1152/physrev.00010.2016] [Citation(s) in RCA: 340] [Impact Index Per Article: 48.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Investigations in the last 10 years have revealed a new category of neurological diseases mediated by antibodies against cell surface and synaptic proteins. There are currently 16 such diseases all characterized by autoantibodies against neuronal proteins involved in synaptic signaling and plasticity. In clinical practice these findings have changed the diagnostic and treatment approach to potentially lethal, but now treatable, neurological and psychiatric syndromes previously considered idiopathic or not even suspected to be immune-mediated. Studies show that patients' antibodies can impair the surface dynamics of the target receptors eliminating them from synapses (e.g., NMDA receptor), block the function of the antigens without changing their synaptic density (e.g., GABAb receptor), interfere with synaptic protein-protein interactions (LGI1, Caspr2), alter synapse formation (e.g., neurexin-3α), or by unclear mechanisms associate to a new form of tauopathy (IgLON5). Here we first trace the process of discovery of these diseases, describing the triggers and symptoms related to each autoantigen, and then review in detail the structural and functional alterations caused by the autoantibodies with special emphasis in those (NMDA receptor, amphiphysin) that have been modeled in animals.
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Affiliation(s)
- Josep Dalmau
- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain; Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania; Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain; Hans-Berger Department of Neurology, Jena University Hospital, Jena, Germany; Servei de Neurologia, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain
| | - Christian Geis
- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain; Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania; Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain; Hans-Berger Department of Neurology, Jena University Hospital, Jena, Germany; Servei de Neurologia, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain
| | - Francesc Graus
- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain; Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania; Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain; Hans-Berger Department of Neurology, Jena University Hospital, Jena, Germany; Servei de Neurologia, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain
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7
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Winther ÅME, Vorontsova O, Rees KA, Näreoja T, Sopova E, Jiao W, Shupliakov O. An Endocytic Scaffolding Protein together with Synapsin Regulates Synaptic Vesicle Clustering in the Drosophila Neuromuscular Junction. J Neurosci 2015; 35:14756-70. [PMID: 26538647 PMCID: PMC6605226 DOI: 10.1523/jneurosci.1675-15.2015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Revised: 09/16/2015] [Accepted: 09/25/2015] [Indexed: 11/21/2022] Open
Abstract
Many endocytic proteins accumulate in the reserve pool of synaptic vesicles (SVs) in synapses and relocalize to the endocytic periactive zone during neurotransmitter release. Currently little is known about their functions outside the periactive zone. Here we show that in the Drosophila neuromuscular junction (NMJ), the endocytic scaffolding protein Dap160 colocalizes during the SV cycle and forms a functional complex with the SV-associated phosphoprotein synapsin, previously implicated in SV clustering. This direct interaction is strongly enhanced under phosphorylation-promoting conditions and is essential for proper localization of synapsin at NMJs. In a dap160 rescue mutant lacking the interaction between Dap160 and synapsin, perturbed reclustering of SVs during synaptic activity is observed. Our data indicate that in addition to the function in endocytosis, Dap160 is a component of a network of protein-protein interactions that serves for clustering of SVs in conjunction with synapsin. During the SV cycle, Dap160 interacts with synapsin dispersed from SVs and helps direct synapsin back to vesicles. The proteins function in synergy to achieve efficient clustering of SVs in the reserve pool. SIGNIFICANCE STATEMENT We provide the first evidence for the function of the SH3 domain interaction in synaptic vesicle (SV) organization at the synaptic active zone. Using Drosophila neuromuscular junction as a model synapse, we describe the molecular mechanism that enables the protein implicated in SV clustering, synapsin, to return to the pool of vesicles during neurotransmitter release. We also identify the endocytic scaffolding complex that includes Dap160 as a regulator of the events linking exocytosis and endocytosis in synapses.
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Affiliation(s)
- Åsa M E Winther
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Olga Vorontsova
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Kathryn A Rees
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Tuomas Näreoja
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Elena Sopova
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Wei Jiao
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Oleg Shupliakov
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
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8
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Shupliakov O, Haucke V, Pechstein A. How synapsin I may cluster synaptic vesicles. Semin Cell Dev Biol 2011; 22:393-9. [DOI: 10.1016/j.semcdb.2011.07.006] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Accepted: 07/13/2011] [Indexed: 12/14/2022]
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Pechstein A, Shupliakov O. Taking a back seat: synaptic vesicle clustering in presynaptic terminals. Front Synaptic Neurosci 2010; 2:143. [PMID: 21423529 PMCID: PMC3059686 DOI: 10.3389/fnsyn.2010.00143] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Accepted: 08/23/2010] [Indexed: 11/13/2022] Open
Abstract
Central inter-neuronal synapses employ various molecular mechanisms to sustain neurotransmitter release during phases of high-frequency synaptic activity. One of the features ensuring this property is the presence of a pool of synaptic vesicles (SVs) in the presynaptic terminal. At rest and low rates of stimulation, most of the vesicles composing this pool remain in a tight cluster. They are actively utilized when neurons fire action potentials at higher rates and the capability of the recycling machinery is limited. In addition, SV clusters are capable of migrating between release sites and reassemble into clusters at neighboring active zones (AZs). Within the cluster, thin "tethers" interconnect SVs. These dynamic filamentous structures are reorganized during stimulation thereby releasing SVs from the cluster. So far, one protein family, the synapsins, which bind actin filaments and vesicles in a phosphorylation-dependent manner, has been implicated in SV clustering in vertebrate synapses. As evident from recent studies, many endocytic proteins reside in the SV cluster in addition to synapsin. Here we discuss alternative possible mechanisms involved in the organization of this population of SVs. We propose a model in which synapsins together with other synaptic proteins, a large proportion of which is involved in SV recycling, form a dynamic proteinaceous "matrix" which limits the mobility of SVs. Actin filaments, however, do not seem to contribute to SV crosslinking within the SV cluster, but instead they are present peripherally to it, at sites of neurotransmitter release, and at sites of SV recycling.
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Affiliation(s)
- Arndt Pechstein
- Department of Neuroscience, Developmental Biology for Regenerative Medicine, Karolinska Institutet Stockholm, Sweden
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10
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Abstract
Central nerve terminals release neurotransmitter in response to a wide variety of stimuli. Because maintenance of neurotransmitter release is dependent on the continual supply of synaptic vesicles (SVs), nerve terminals possess an array of endocytosis modes to retrieve and recycle SV membrane and proteins. During mild stimulation conditions, single SV retrieval modes such as clathrin-mediated endocytosis predominate. However, during increased neuronal activity, additional SV retrieval capacity is required, which is provided by activity-dependent bulk endocytosis (ADBE). ADBE is the dominant SV retrieval mechanism during elevated neuronal activity. It is a high capacity SV retrieval mode that is immediately triggered during such stimulation conditions. This review will summarize the current knowledge regarding the molecular mechanism of ADBE, including molecules required for its triggering and subsequent steps, including SV budding from bulk endosomes. The molecular relationship between ADBE and the SV reserve pool will also be discussed. It is becoming clear that an understanding of the molecular physiology of ADBE will be of critical importance in attempts to modulate both normal and abnormal synaptic function during intense neuronal activity.
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Affiliation(s)
- Emma L. Clayton
- Membrane Biology Group, Centre for Integrative Physiology, George Square, University of Edinburgh, EH8 9XD, Scotland, U.K
| | - Michael A. Cousin
- Membrane Biology Group, Centre for Integrative Physiology, George Square, University of Edinburgh, EH8 9XD, Scotland, U.K
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Thomas S, Ritter B, Verbich D, Sanson C, Bourbonnière L, McKinney RA, McPherson PS. Intersectin regulates dendritic spine development and somatodendritic endocytosis but not synaptic vesicle recycling in hippocampal neurons. J Biol Chem 2009; 284:12410-9. [PMID: 19258322 DOI: 10.1074/jbc.m809746200] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Intersectin-short (intersectin-s) is a multimodule scaffolding protein functioning in constitutive and regulated forms of endocytosis in non-neuronal cells and in synaptic vesicle (SV) recycling at the neuromuscular junction of Drosophila and Caenorhabditis elegans. In vertebrates, alternative splicing generates a second isoform, intersectin-long (intersectin-l), that contains additional modular domains providing a guanine nucleotide exchange factor activity for Cdc42. In mammals, intersectin-s is expressed in multiple tissues and cells, including glia, but excluded from neurons, whereas intersectin-l is a neuron-specific isoform. Thus, intersectin-I may regulate multiple forms of endocytosis in mammalian neurons, including SV endocytosis. We now report, however, that intersectin-l is localized to somatodendritic regions of cultured hippocampal neurons, with some juxtanuclear accumulation, but is excluded from synaptophysin-labeled axon terminals. Consistently, intersectin-l knockdown (KD) does not affect SV recycling. Instead intersectin-l co-localizes with clathrin heavy chain and adaptor protein 2 in the somatodendritic region of neurons, and its KD reduces the rate of transferrin endocytosis. The protein also co-localizes with F-actin at dendritic spines, and intersectin-l KD disrupts spine maturation during development. Our data indicate that intersectin-l is indeed an important regulator of constitutive endocytosis and neuronal development but that it is not a prominent player in the regulated endocytosis of SVs.
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Affiliation(s)
- Sébastien Thomas
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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12
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The synaptic vesicle cluster: A source of endocytic proteins during neurotransmitter release. Neuroscience 2009; 158:204-10. [DOI: 10.1016/j.neuroscience.2008.03.035] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Revised: 03/17/2008] [Accepted: 03/18/2008] [Indexed: 12/11/2022]
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Owe SG, Jensen V, Evergren E, Ruiz A, Shupliakov O, Kullmann DM, Storm-Mathisen J, Walaas SI, Hvalby Ø, Bergersen LH. Synapsin- and actin-dependent frequency enhancement in mouse hippocampal mossy fiber synapses. Cereb Cortex 2008; 19:511-23. [PMID: 18550596 PMCID: PMC2638812 DOI: 10.1093/cercor/bhn101] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The synapsin proteins have different roles in excitatory and inhibitory synaptic terminals. We demonstrate a differential role between types of excitatory terminals. Structural and functional aspects of the hippocampal mossy fiber (MF) synapses were studied in wild-type (WT) mice and in synapsin double-knockout mice (DKO). A severe reduction in the number of synaptic vesicles situated more than 100 nm away from the presynaptic membrane active zone was found in the synapsin DKO animals. The ultrastructural level gave concomitant reduction in F-actin immunoreactivity observed at the periactive endocytic zone of the MF terminals. Frequency facilitation was normal in synapsin DKO mice at low firing rates (approximately 0.1 Hz) but was impaired at firing rates within the physiological range (approximately 2 Hz). Synapses made by associational/commissural fibers showed comparatively small frequency facilitation at the same frequencies. Synapsin-dependent facilitation in MF synapses of WT mice was attenuated by blocking F-actin polymerization with cytochalasin B in hippocampal slices. Synapsin III, selectively seen in MF synapses, is enriched specifically in the area adjacent to the synaptic cleft. This may underlie the ability of synapsin III to promote synaptic depression, contributing to the reduced frequency facilitation observed in the absence of synapsins I and II.
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Affiliation(s)
- Simen G Owe
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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14
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Cell- and stimulus-dependent heterogeneity of synaptic vesicle endocytic recycling mechanisms revealed by studies of dynamin 1-null neurons. Proc Natl Acad Sci U S A 2008; 105:2175-80. [PMID: 18250322 DOI: 10.1073/pnas.0712171105] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mice lacking expression of dynamin 1, a GTPase implicated in the fission reaction of synaptic vesicle endocytosis, fail to thrive and exhibit severe activity-dependent endocytic defects at their synapses. Here, we have used electron tomography to investigate the massive increase in clathrin-coated pit abundance that is selectively observed at a subset of synapses in dynamin 1 KO primary neuron cultures under conditions of spontaneous network activity. This increase, leading to branched tubular plasma membrane invaginations capped by clathrin-coated buds, occurs selectively at inhibitory synapses. A similar massive increase of clathrin-coated profiles (in this case, of clathrin-coated vesicles) is observed at inhibitory synapses of neurons that lack expression of synaptojanin 1, a phosphoinositide phosphatase involved in clathrin-coated vesicle uncoating. Thus, although excitatory synapses are largely spared under these conditions, inhibitory synapses are uniquely sensitive to perturbation of endocytic proteins, probably as a result of their higher levels of tonic activity leading to a buildup of clathrin-coated intermediates in these synapses. In contrast, the predominant endocytic structures observed at the majority of dynamin 1 KO synapses after acute stimulation are endosome-like intermediates that originate by a dynamin 1-independent form of endocytosis. These findings reveal a striking heterogeneity in the mode of synaptic vesicle recycling in different synapses and functional states.
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Evergren E, Benfenati F, Shupliakov O. The synapsin cycle: a view from the synaptic endocytic zone. J Neurosci Res 2008; 85:2648-56. [PMID: 17455288 DOI: 10.1002/jnr.21176] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Although the synapsin phosphoproteins were discovered more than 30 years ago and are known to play important roles in neurotransmitter release and synaptogenesis, a complete picture of their functions within the nerve terminal is lacking. It has been shown that these proteins play an important role in the clustering of synaptic vesicles (SVs) at active zones and function as modulators of synaptic strength by acting at both pre- and postdocking levels. Recent studies have demonstrated that synapsins migrate to the endocytic zone of central synapses during neurotransmitter release, which suggests that there are additional functions for these proteins in SV recycling.
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Affiliation(s)
- E Evergren
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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16
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Evergren E, Gad H, Walther K, Sundborger A, Tomilin N, Shupliakov O. Intersectin is a negative regulator of dynamin recruitment to the synaptic endocytic zone in the central synapse. J Neurosci 2007; 27:379-90. [PMID: 17215399 PMCID: PMC6672076 DOI: 10.1523/jneurosci.4683-06.2007] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 11/27/2006] [Accepted: 11/27/2006] [Indexed: 11/21/2022] Open
Abstract
Intersectin is a multidomain dynamin-binding protein implicated in numerous functions in the nervous system, including synapse formation and endocytosis. Here, we demonstrate that during neurotransmitter release in the central synapse, intersectin, like its binding partner dynamin, is redistributed from the synaptic vesicle pool to the periactive zone. Acute perturbation of the intersectin-dynamin interaction by microinjection of either intersectin antibodies or Src homology 3 (SH3) domains inhibited endocytosis at the fission step. Although the morphological effects induced by the different reagents were similar, antibody injections resulted in a dramatic increase in dynamin immunoreactivity around coated pits and at constricted necks, whereas synapses microinjected with the GST (glutathione S-transferase)-SH3C domain displayed reduced amounts of dynamin in the neck region. Our data suggest that intersectin controls the amount of dynamin released from the synaptic vesicle cluster to the periactive zone and that it may regulate fission of clathrin-coated intermediates.
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Affiliation(s)
- Emma Evergren
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Helge Gad
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Kristin Walther
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Anna Sundborger
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Nikolay Tomilin
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Oleg Shupliakov
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
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Weimer RM, Gracheva EO, Meyrignac O, Miller KG, Richmond JE, Bessereau JL. UNC-13 and UNC-10/rim localize synaptic vesicles to specific membrane domains. J Neurosci 2006; 26:8040-7. [PMID: 16885217 PMCID: PMC3874421 DOI: 10.1523/jneurosci.2350-06.2006] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptic vesicles undergo a maturation step, termed priming, in which they become competent to fuse with the plasma membrane. To morphologically define the site of vesicle priming and identify fusion-competent synaptic vesicles, we combined a rapid physical-fixation technique with immunogold staining and high-resolution morphometric analysis at Caenorhabditis elegans neuromuscular junctions. In these presynaptic terminals, a subset of synaptic vesicles contact the plasma membrane within approximately 100 nm of a presynaptic dense projection. UNC-13, a protein required for vesicle priming, localizes to this same region of the plasma membrane. In an unc-13 null mutant, few synaptic vesicles contact the plasma membrane, suggesting that membrane-contacting synaptic vesicles represent the morphological correlates of primed vesicles. Interestingly, a subpopulation of membrane-contacting vesicles, located within 30 nm of a dense projection, are unperturbed in unc-13 mutants. We show that UNC-10/Rim, a protein implicated in presynaptic plasticity, localizes to dense projections and that loss of UNC-10/Rim causes an UNC-13-independent reduction in membrane-contacting synaptic vesicles within 30 nm of the dense projections. Our data together identify a discrete domain for vesicle priming within 100 nm of dense projections and further suggest that UNC-10/Rim and UNC-13 separately contribute to the membrane localization of synaptic vesicles within this domain.
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