1
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Patzke C, Brockmann MM, Dai J, Gan KJ, Grauel MK, Fenske P, Liu Y, Acuna C, Rosenmund C, Südhof TC. Neuromodulator Signaling Bidirectionally Controls Vesicle Numbers in Human Synapses. Cell 2020; 179:498-513.e22. [PMID: 31585084 DOI: 10.1016/j.cell.2019.09.011] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 06/28/2019] [Accepted: 09/06/2019] [Indexed: 10/25/2022]
Abstract
Neuromodulators bind to pre- and postsynaptic G protein-coupled receptors (GPCRs), are able to quickly change intracellular cyclic AMP (cAMP) and Ca2+ levels, and are thought to play important roles in neuropsychiatric and neurodegenerative diseases. Here, we discovered in human neurons an unanticipated presynaptic mechanism that acutely changes synaptic ultrastructure and regulates synaptic communication. Activation of neuromodulator receptors bidirectionally controlled synaptic vesicle numbers within nerve terminals. This control correlated with changes in the levels of cAMP-dependent protein kinase A-mediated phosphorylation of synapsin-1. Using a conditional deletion approach, we reveal that the neuromodulator-induced control of synaptic vesicle numbers was largely dependent on synapsin-1. We propose a mechanism whereby non-phosphorylated synapsin-1 "latches" synaptic vesicles to presynaptic clusters at the active zone. cAMP-dependent phosphorylation of synapsin-1 then removes the vesicles. cAMP-independent dephosphorylation of synapsin-1 in turn recruits vesicles. Synapsin-1 thereby bidirectionally regulates synaptic vesicle numbers and modifies presynaptic neurotransmitter release as an effector of neuromodulator signaling in human neurons.
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Affiliation(s)
- Christopher Patzke
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA.
| | - Marisa M Brockmann
- Institut für Neurophysiologie, Charité Universitätsmedizin, 10117 Berlin, Germany
| | - Jinye Dai
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA
| | - Kathlyn J Gan
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA
| | - M Katharina Grauel
- Institut für Neurophysiologie, Charité Universitätsmedizin, 10117 Berlin, Germany
| | - Pascal Fenske
- Institut für Neurophysiologie, Charité Universitätsmedizin, 10117 Berlin, Germany
| | - Yu Liu
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA
| | - Claudio Acuna
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA
| | - Christian Rosenmund
- Institut für Neurophysiologie, Charité Universitätsmedizin, 10117 Berlin, Germany
| | - Thomas C Südhof
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA
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2
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Rocchi A, Sacchetti S, De Fusco A, Giovedi S, Parisi B, Cesca F, Höltje M, Ruprecht K, Ahnert-Hilger G, Benfenati F. Autoantibodies to synapsin I sequestrate synapsin I and alter synaptic function. Cell Death Dis 2019; 10:864. [PMID: 31727880 PMCID: PMC6856194 DOI: 10.1038/s41419-019-2106-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 10/25/2019] [Accepted: 10/31/2019] [Indexed: 12/18/2022]
Abstract
Synapsin I is a phosphoprotein that coats the cytoplasmic side of synaptic vesicles and regulates their trafficking within nerve terminals. Autoantibodies against Syn I have been described in sera and cerebrospinal fluids of patients with numerous neurological diseases, including limbic encephalitis and clinically isolated syndrome; however, the effects and fate of autoantibodies in neurons are still unexplored. We found that in vitro exposure of primary hippocampal neurons to patient’s autoantibodies to SynI decreased the density of excitatory and inhibitory synapses and impaired both glutamatergic and GABAergic synaptic transmission. These effects were reproduced with a purified SynI antibody and completely absent in SynI knockout neurons. Autoantibodies to SynI are internalized by FcγII/III-mediated endocytosis, interact with endogenous SynI, and promote its sequestration and intracellular aggregation. Neurons exposed to human autoantibodies to SynI display a reduced density of SVs, mimicking the SynI loss-of-function phenotype. Our data indicate that autoantibodies to intracellular antigens such as SynI can reach and inactivate their targets and suggest that an antibody-mediated synaptic dysfunction may contribute to the evolution and progression of autoimmune-mediated neurological diseases positive for SynI autoantibodies.
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Affiliation(s)
- Anna Rocchi
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy
| | - Silvio Sacchetti
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy
| | - Antonio De Fusco
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Silvia Giovedi
- IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Barbara Parisi
- IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Fabrizia Cesca
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Life Science, University of Trieste, via Giorgieri, 5, 34127, Trieste, Italy
| | - Markus Höltje
- Institute of Integrative Neuroanatomy, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Klemens Ruprecht
- Department of Neurology, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Gudrun Ahnert-Hilger
- Institute of Integrative Neuroanatomy, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy. .,IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.
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3
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Marte A, Russo I, Rebosio C, Valente P, Belluzzi E, Pischedda F, Montani C, Lavarello C, Petretto A, Fedele E, Baldelli P, Benfenati F, Piccoli G, Greggio E, Onofri F. Leucine‐rich repeat kinase 2 phosphorylation on synapsin I regulates glutamate release at pre‐synaptic sites. J Neurochem 2019; 150:264-281. [PMID: 31148170 DOI: 10.1111/jnc.14778] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 05/20/2019] [Accepted: 05/28/2019] [Indexed: 12/25/2022]
Abstract
Leucine-rich repeat kinase 2 (LRRK2) is a large multidomain scaffolding protein with kinase and GTPase activities involved in synaptic vesicle (SV) dynamics. While its role in Parkinson's disease has been largely investigated, little is known about LRRK2 physiological role and until now few proteins have been described as substrates. We have previously demonstrated that LRRK2 through its WD40 domain interacts with synapsin I, an important SV-associated phosphoprotein involved in neuronal development and in the regulation of neurotransmitter release. To test whether synapsin I is substrate for LRRK2 and characterize the properties of its phosphorylation, we used in vitro kinase and binding assays as well as cellular model and site-direct mutagenesis. Using synaptosomes in superfusion, patch-clamp recordings in autaptic WT and synapsin I KO cortical neurons and SypHy assay on primary cortical culture from wild-type and BAC human LRRK2 G2019S mice we characterized the role of LRRK2 kinase activity on glutamate release and SV trafficking. Here we reported that synapsin I is phosphorylated by LRRK2 and demonstrated that the interaction between LRRK2 WD40 domain and synapsin I is crucial for this phosphorylation. Moreover, we showed that LRRK2 phosphorylation of synapsin I at threonine 337 and 339 significantly reduces synapsin I-SV/actin interactions. Using complementary experimental approaches, we demonstrated that LRRK2 controls glutamate release and SV dynamics in a kinase activity and synapsin I-dependent manner. Our findings show that synapsin I is a LRRK2 substrate and describe a novel mechanisms of regulation of glutamate release by LRRK2 kinase activity.
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Affiliation(s)
- Antonella Marte
- Department of Experimental Medicine University of Genova Genova Italy
| | | | | | - Pierluigi Valente
- Department of Experimental Medicine University of Genova Genova Italy
- IRCCS Ospedale Policlinico San Martino Genova Italy
| | - Elisa Belluzzi
- Rheumatology Unit, Department of Medicine‐DIMED University Hospital of Padova Padova Italy
| | - Francesca Pischedda
- Center for Integrative Biology (CIBIO) University of Trento Trento Italy
- Dulbecco Telethon Institute Trento Italy
| | - Caterina Montani
- Center for Integrative Biology (CIBIO) University of Trento Trento Italy
- Dulbecco Telethon Institute Trento Italy
| | - Chiara Lavarello
- Laboratory of Mass Spectrometry ‐ Core Facilities Istituto Giannina Gaslini Genova Italy
| | - Andrea Petretto
- Laboratory of Mass Spectrometry ‐ Core Facilities Istituto Giannina Gaslini Genova Italy
| | - Ernesto Fedele
- Department of Pharmacy University of Genova Genova Italy
- IRCCS Ospedale Policlinico San Martino Genova Italy
| | - Pietro Baldelli
- Department of Experimental Medicine University of Genova Genova Italy
- IRCCS Ospedale Policlinico San Martino Genova Italy
| | - Fabio Benfenati
- IRCCS Ospedale Policlinico San Martino Genova Italy
- Center for Synaptic Neuroscience and Technology Istituto Italiano di Tecnologia Genova Italy
| | - Giovanni Piccoli
- Center for Integrative Biology (CIBIO) University of Trento Trento Italy
- Dulbecco Telethon Institute Trento Italy
| | - Elisa Greggio
- Department of Biology University of Padova Padova Italy
| | - Franco Onofri
- Department of Experimental Medicine University of Genova Genova Italy
- IRCCS Ospedale Policlinico San Martino Genova Italy
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4
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Mertens R, Melchert S, Gitler D, Schou MB, Saether SG, Vaaler A, Piepgras J, Kochova E, Benfenati F, Ahnert-Hilger G, Ruprecht K, Höltje M. Epitope specificity of anti-synapsin autoantibodies: Differential targeting of synapsin I domains. PLoS One 2018; 13:e0208636. [PMID: 30543686 PMCID: PMC6292584 DOI: 10.1371/journal.pone.0208636] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Accepted: 11/20/2018] [Indexed: 01/07/2023] Open
Abstract
OBJECTIVE To identify the specific domains of the presynaptic protein synapsin targeted by recently described autoantibodies to synapsin. METHODS Sera of 20 and CSF of two patients with different psychiatric and neurological disorders previously tested positive for immunoglobulin (Ig)G antibodies to full-length synapsin were screened for IgG against synapsin I domains using HEK293 cells transfected with constructs encoding different domains of rat synapsin Ia. Additionally, IgG subclasses were determined using full-length synapsin Ia. Serum and CSF from one patient were also screened for IgA autoantibodies to synapsin I domains. Sera from nine and CSF from two healthy subjects were analyzed as controls. RESULTS IgG in serum from 12 of 20 IgG synapsin full-length positive patients, but from none of the healthy controls, bound to synapsin domains. Of these 12 sera, six bound to the A domain, five to the D domain, and one to the B- (and possibly A-), D-, and E-domains of synapsin I. IgG antibodies to the D-domain were also detected in one of the CSF samples. Determination of IgG subclasses detected IgG1 in two sera and one CSF, IgG2 in none of the samples, IgG3 in two sera, and IgG4 in eight sera. One patient known to be positive for IgA antibodies to full-length synapsin had IgA antibodies to the D-domain in serum and CSF. CONCLUSIONS Anti-synapsin autoantibodies preferentially bind to either the A- or the D-domain of synapsin I.
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Affiliation(s)
- Robert Mertens
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Sarah Melchert
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Daniel Gitler
- Department of Physiology and Cell Biology, Faculty of Health Sciences and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Morten Brix Schou
- Department of Psychiatry, St. Olav’s University Hospital, Trondheim, Norway
- Department of Mental Health, Norwegian University of Science and Technology, Trondheim, Norway
| | - Sverre Georg Saether
- Department of Psychiatry, St. Olav’s University Hospital, Trondheim, Norway
- Department of Mental Health, Norwegian University of Science and Technology, Trondheim, Norway
| | - Arne Vaaler
- Department of Psychiatry, St. Olav’s University Hospital, Trondheim, Norway
- Department of Mental Health, Norwegian University of Science and Technology, Trondheim, Norway
| | - Johannes Piepgras
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Elena Kochova
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Genova, Italy
| | - Gudrun Ahnert-Hilger
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Klemens Ruprecht
- Department of Neurology, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Markus Höltje
- Institute of Integrative Neuroanatomy, Charité –Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
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5
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Guarnieri FC, Bellani S, Yekhlef L, Bergamaschi A, Finardi A, Fesce R, Pozzi D, Monzani E, Fornasiero EF, Matteoli M, Martino G, Furlan R, Taverna S, Muzio L, Valtorta F. Synapsin I deletion reduces neuronal damage and ameliorates clinical progression of experimental autoimmune encephalomyelitis. Brain Behav Immun 2018; 68:197-210. [PMID: 29066310 DOI: 10.1016/j.bbi.2017.10.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 10/10/2017] [Accepted: 10/20/2017] [Indexed: 11/20/2022] Open
Abstract
The classical view of multiple sclerosis (MS) pathogenesis states that inflammation-mediated demyelination is responsible for neuronal damage and loss. However, recent findings show that impairment of neuronal functions and demyelination can be independent events, suggesting the coexistence of other pathogenic mechanisms. Due to the inflammatory milieu, subtle alterations in synaptic function occur, which are probably at the basis of the early cognitive decline that often precedes the neurodegenerative phases in MS patients. In particular, it has been reported that inflammation enhances excitatory synaptic transmission while it decreases GABAergic transmission in vitro and ex vivo. This evidence points to the idea that an excitation/inhibition imbalance occurs in the inflamed MS brain, even though the exact molecular mechanisms leading to this synaptic dysfunction are as yet not completely clear. Along this line, we observed that acute treatment of primary hippocampal neurons in culture with pro-inflammatory cytokines leads to an increased phosphorylation of synapsin I (SynI) by ERK1/2 kinase and to an increase in the frequency of spontaneous synaptic vesicle release events, which is prevented by SynI deletion. In vivo, the ablation of SynI expression is protective in terms of disease progression and neuronal damage in the experimental autoimmune encephalomyelitis mouse model of MS. Our results point to a possible key role in MS pathogenesis of the neuronal protein SynI, a regulator of excitation/inhibition balance in neuronal networks.
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Affiliation(s)
- Fabrizia C Guarnieri
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy; Vita-Salute San Raffaele University, Via Olgettina 58, 20132 Milan, Italy
| | - Serena Bellani
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Latefa Yekhlef
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Andrea Bergamaschi
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Annamaria Finardi
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Riccardo Fesce
- Centre of Neuroscience and DISTA, University of Insubria, Via Ravasi 2, 21100 Varese, Italy
| | - Davide Pozzi
- Humanitas Clinical and Research Centre, Via Manzoni 113, 20089 Rozzano, Milan, Italy
| | - Elena Monzani
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Eugenio F Fornasiero
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Michela Matteoli
- Humanitas Clinical and Research Centre, Via Manzoni 113, 20089 Rozzano, Milan, Italy; CNR Institute of Neuroscience, via Vanvitelli 32, 20129 Milan, Italy
| | - Gianvito Martino
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy; Vita-Salute San Raffaele University, Via Olgettina 58, 20132 Milan, Italy
| | - Roberto Furlan
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Stefano Taverna
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Luca Muzio
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy
| | - Flavia Valtorta
- Division of Neuroscience, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy; Vita-Salute San Raffaele University, Via Olgettina 58, 20132 Milan, Italy.
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6
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Marcotulli D, Fattorini G, Bragina L, Perugini J, Conti F. Levetiracetam Affects Differentially Presynaptic Proteins in Rat Cerebral Cortex. Front Cell Neurosci 2017; 11:389. [PMID: 29311825 PMCID: PMC5732259 DOI: 10.3389/fncel.2017.00389] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 11/24/2017] [Indexed: 01/23/2023] Open
Abstract
Presynaptic proteins are potential therapeutic targets for epilepsy and other neurological diseases. We tested the hypothesis that chronic treatment with the SV2A ligand levetiracetam affects the expression of other presynaptic proteins. Results showed that in rat neocortex no significant difference was detected in SV2A protein levels in levetiracetam treated animals compared to controls, whereas levetiracetam post-transcriptionally decreased several vesicular proteins and increased LRRK2, without any change in mRNA levels. Analysis of SV2A interactome indicates that the presynaptic proteins regulation induced by levetiracetam reported here is mediated by this interactome, and suggests that LRRK2 plays a role in forging the pattern of effects.
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Affiliation(s)
- Daniele Marcotulli
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy
| | - Giorgia Fattorini
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy.,Center for Neurobiology of Aging, INRCA IRCCS, Ancona, Italy
| | - Luca Bragina
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy.,Center for Neurobiology of Aging, INRCA IRCCS, Ancona, Italy
| | - Jessica Perugini
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy
| | - Fiorenzo Conti
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy.,Center for Neurobiology of Aging, INRCA IRCCS, Ancona, Italy
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7
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Heise C, Taha E, Murru L, Ponzoni L, Cattaneo A, Guarnieri FC, Montani C, Mossa A, Vezzoli E, Ippolito G, Zapata J, Barrera I, Ryazanov AG, Cook J, Poe M, Stephen MR, Kopanitsa M, Benfante R, Rusconi F, Braida D, Francolini M, Proud CG, Valtorta F, Passafaro M, Sala M, Bachi A, Verpelli C, Rosenblum K, Sala C. eEF2K/eEF2 Pathway Controls the Excitation/Inhibition Balance and Susceptibility to Epileptic Seizures. Cereb Cortex 2017; 27:2226-2248. [PMID: 27005990 DOI: 10.1093/cercor/bhw075] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Alterations in the balance of inhibitory and excitatory synaptic transmission have been implicated in the pathogenesis of neurological disorders such as epilepsy. Eukaryotic elongation factor 2 kinase (eEF2K) is a highly regulated, ubiquitous kinase involved in the control of protein translation. Here, we show that eEF2K activity negatively regulates GABAergic synaptic transmission. Indeed, loss of eEF2K increases GABAergic synaptic transmission by upregulating the presynaptic protein Synapsin 2b and α5-containing GABAA receptors and thus interferes with the excitation/inhibition balance. This cellular phenotype is accompanied by an increased resistance to epilepsy and an impairment of only a specific hippocampal-dependent fear conditioning. From a clinical perspective, our results identify eEF2K as a potential novel target for antiepileptic drugs, since pharmacological and genetic inhibition of eEF2K can revert the epileptic phenotype in a mouse model of human epilepsy.
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Affiliation(s)
| | - Elham Taha
- Sagol Department of Neurobiology, University of Haifa, Haifa, Israel.,Center for Gene Manipulation in the Brain, Natural Science Faculty, University of Haifa, Haifa, Israel
| | - Luca Murru
- CNR Neuroscience Institute, Milan, Italy
| | - Luisa Ponzoni
- Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | | | - Fabrizia C Guarnieri
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| | | | | | - Elena Vezzoli
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | | | | | - Iliana Barrera
- Sagol Department of Neurobiology and.,Center for Gene Manipulation in the Brain, Natural Science Faculty, University of Haifa, Haifa, Israel
| | - Alexey G Ryazanov
- The Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - James Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Michael Poe
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Michael Rajesh Stephen
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Maksym Kopanitsa
- Synome, Babraham Research Campus, Cambridge CB22 3AT, UK.,Charles River Discovery Research Services, 70210 Kuopio, Finland
| | - Roberta Benfante
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Francesco Rusconi
- Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Daniela Braida
- Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Maura Francolini
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Christopher G Proud
- University of Southampton, Centre for Biological Sciences, Southampton SO17 1BJ, UK.,South Australian Health and Medical Research Institute and University of Adelaide, Adelaide, Australia
| | - Flavia Valtorta
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| | - Maria Passafaro
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Mariaelvina Sala
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Angela Bachi
- IFOM-FIRC Institute of Molecular Oncology, Milan, Italy
| | - Chiara Verpelli
- CNR Neuroscience Institute, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Kobi Rosenblum
- Sagol Department of Neurobiology and.,Center for Gene Manipulation in the Brain, Natural Science Faculty, University of Haifa, Haifa, Israel
| | - Carlo Sala
- CNR Neuroscience Institute, Milan, Italy, Università degli Studi di Milano, Milan, Italy.,Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
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8
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Corradi A, Fadda M, Piton A, Patry L, Marte A, Rossi P, Cadieux-Dion M, Gauthier J, Lapointe L, Mottron L, Valtorta F, Rouleau GA, Fassio A, Benfenati F, Cossette P. SYN2 is an autism predisposing gene: loss-of-function mutations alter synaptic vesicle cycling and axon outgrowth. Hum Mol Genet 2013; 23:90-103. [PMID: 23956174 PMCID: PMC3857945 DOI: 10.1093/hmg/ddt401] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
An increasing number of genes predisposing to autism spectrum disorders (ASDs) has been identified, many of which are implicated in synaptic function. This 'synaptic autism pathway' notably includes disruption of SYN1 that is associated with epilepsy, autism and abnormal behavior in both human and mice models. Synapsins constitute a multigene family of neuron-specific phosphoproteins (SYN1-3) present in the majority of synapses where they are implicated in the regulation of neurotransmitter release and synaptogenesis. Synapsins I and II, the major Syn isoforms in the adult brain, display partially overlapping functions and defects in both isoforms are associated with epilepsy and autistic-like behavior in mice. In this study, we show that nonsense (A94fs199X) and missense (Y236S and G464R) mutations in SYN2 are associated with ASD in humans. The phenotype is apparent in males. Female carriers of SYN2 mutations are unaffected, suggesting that SYN2 is another example of autosomal sex-limited expression in ASD. When expressed in SYN2 knockout neurons, wild-type human Syn II fully rescues the SYN2 knockout phenotype, whereas the nonsense mutant is not expressed and the missense mutants are virtually unable to modify the SYN2 knockout phenotype. These results identify for the first time SYN2 as a novel predisposing gene for ASD and strengthen the hypothesis that a disturbance of synaptic homeostasis underlies ASD.
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Affiliation(s)
- Anna Corradi
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
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9
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Medrihan L, Cesca F, Raimondi A, Lignani G, Baldelli P, Benfenati F. Synapsin II desynchronizes neurotransmitter release at inhibitory synapses by interacting with presynaptic calcium channels. Nat Commun 2013; 4:1512. [PMID: 23443540 PMCID: PMC3586721 DOI: 10.1038/ncomms2515] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 01/18/2013] [Indexed: 01/05/2023] Open
Abstract
In the central nervous system, most synapses show a fast mode of neurotransmitter release known as synchronous release followed by a phase of asynchronous release, which extends over tens of milliseconds to seconds. Synapsin II (SYN2) is a member of the multigene synapsin family (SYN1/2/3) of synaptic vesicle phosphoproteins that modulate synaptic transmission and plasticity, and are mutated in epileptic patients. Here we report that inhibitory synapses of the dentate gyrus of Syn II knockout mice display an upregulation of synchronous neurotransmitter release and a concomitant loss of delayed asynchronous release. Syn II promotes γ-aminobutyric acid asynchronous release in a Ca2+-dependent manner by a functional interaction with presynaptic Ca2+ channels, revealing a new role in synaptic transmission for synapsins. The arrival of action potentials at nerve terminals often leads to synchronous neurotransmitter release. Medrihan and colleagues use electrophysiology on mouse hippocampal neurons to show that the vesicle protein Synapsin II promotes GABAergic asynchronous release by interacting with calcium channels.
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Affiliation(s)
- Lucian Medrihan
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy.
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10
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Milanese M, Zappettini S, Onofri F, Musazzi L, Tardito D, Bonifacino T, Messa M, Racagni G, Usai C, Benfenati F, Popoli M, Bonanno G. Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis. J Neurochem 2011; 116:1028-42. [PMID: 21175617 DOI: 10.1111/j.1471-4159.2010.07155.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.
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Affiliation(s)
- Marco Milanese
- Department of Experimental Medicine, University of Genova, Genova, Italy
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11
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Chiappalone M, Casagrande S, Tedesco M, Valtorta F, Baldelli P, Martinoia S, Benfenati F. Opposite Changes in Glutamatergic and GABAergic Transmission Underlie the Diffuse Hyperexcitability of Synapsin I–Deficient Cortical Networks. Cereb Cortex 2008; 19:1422-39. [DOI: 10.1093/cercor/bhn182] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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12
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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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13
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Lack of synapsin I reduces the readily releasable pool of synaptic vesicles at central inhibitory synapses. J Neurosci 2007; 27:13520-31. [PMID: 18057210 DOI: 10.1523/jneurosci.3151-07.2007] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synapsins (Syns) are synaptic vesicle (SV) phosphoproteins that play a role in neurotransmitter release and synaptic plasticity by acting at multiple steps of exocytosis. Mutation of SYN genes results in an epileptic phenotype in mouse and man suggesting a role of Syns in the control of network excitability. We have studied the effects of the genetic ablation of the SYN1 gene on inhibitory synaptic transmission in primary hippocampal neurons. Inhibitory neurons lacking SynI showed reduced amplitude of IPSCs evoked by isolated action potentials. The impairment in inhibitory transmission was caused by a decrease in the size of the SV readily releasable pool, rather than by changes in release probability or quantal size. The reduction of the readily releasable pool was caused by a decrease in the number of SVs released by single synaptic boutons in response to the action potential, in the absence of variations in the number of synaptic contacts between couples of monosynaptically connected neurons. The deletion of SYN1 did not affect paired-pulse depression or post-tetanic potentiation, but was associated with a moderate increase of synaptic depression evoked by trains of action potentials, which became apparent at high stimulation frequencies and was accompanied by a slow down of recovery from depression. The decreased size of the SV readily releasable pool, coupled with a decreased SV recycling rate and refilling by the SV reserve pool, may contribute to the epileptic phenotype of SynI knock-out mice.
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14
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Bragina L, Candiracci C, Barbaresi P, Giovedì S, Benfenati F, Conti F. Heterogeneity of glutamatergic and GABAergic release machinery in cerebral cortex. Neuroscience 2007; 146:1829-40. [PMID: 17445987 DOI: 10.1016/j.neuroscience.2007.02.060] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Revised: 02/21/2007] [Accepted: 02/22/2007] [Indexed: 12/01/2022]
Abstract
We investigated whether cortical glutamatergic and GABAergic release machineries can be differentiated on the basis of the proteins they express, by studying the degree of co-localization of synapsin (SYN) I and II, synaptophysin (SYP) I and II, synaptosomal-associated protein (SNAP)-25 and SNAP-23 in vesicular glutamate transporter (VGLUT) 1-, VGLUT2- and vesicular GABA transporter (VGAT)-positive (+) puncta in the rat cerebral cortex. Co-localization studies showed that SYNI and II were expressed in approximately 90% of VGLUT1+, approximately 30% of VGLUT2+ and 30-50% of VGAT+ puncta; SYPI was expressed in approximately 95% of VGLUT1+, 30% of VGLUT2+, and 45% of VGAT+ puncta; SYPII in approximately 7% of VGLUT1+, 3% of VGLUT2+, and 20% of VGAT+ puncta; SNAP-25 in approximately 94% of VGLUT1+, 5% of VGLUT2+, and 1% of VGAT+ puncta, and SNAP-23 in approximately 3% of VGLUT1+, 86% of VGLUT2+, and 22% of VGAT+ puncta. Since SYPI, which is considered ubiquitous, was expressed in about half of GABAergic axon terminals, we studied its localization electron microscopically and in immunoisolated synaptic vesicles: these studies showed that approximately 30% of axon terminals forming symmetric synapses were SYPI-negative, and that immunoisolated VGAT-positive synaptic vesicles were relatively depleted of SYPI as compared with VGLUT1+ vesicles. Overall, the present investigation shows that in the cerebral cortex of rats distinct presynaptic proteins involved in neurotransmitter release are differentially expressed in GABAergic and in the two major types of glutamatergic axon terminals in the cerebral cortex of rats.
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Affiliation(s)
- L Bragina
- Department of Neuroscience, Università Politecnica delle Marche, Via Tronto 10/A, Torrette di Ancona, I-60020, Ancona, Italy
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15
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Onofri F, Messa M, Matafora V, Bonanno G, Corradi A, Bachi A, Valtorta F, Benfenati F. Synapsin phosphorylation by SRC tyrosine kinase enhances SRC activity in synaptic vesicles. J Biol Chem 2007; 282:15754-67. [PMID: 17400547 DOI: 10.1074/jbc.m701051200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Synapsins are synaptic vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release. Synapsin I is the major binding protein for the SH3 domain of the kinase c-Src in synaptic vesicles. Its binding leads to stimulation of synaptic vesicle-associated c-Src activity. We investigated the mechanism and role of Src activation by synapsins on synaptic vesicles. We found that synapsin is tyrosine phosphorylated by c-Src in vitro and on intact synaptic vesicles independently of its phosphorylation state on serine. Mass spectrometry revealed a single major phosphorylation site at Tyr(301), which is highly conserved in all synapsin isoforms and orthologues. Synapsin tyrosine phosphorylation triggered its binding to the SH2 domains of Src or Fyn. However, synapsin selectively activated and was phosphorylated by Src, consistent with the specific enrichment of c-Src in synaptic vesicles over Fyn or n-Src. The activity of Src on synaptic vesicles was controlled by the amount of vesicle-associated synapsin, which is in turn dependent on synapsin serine phosphorylation. Synaptic vesicles depleted of synapsin in vitro or derived from synapsin null mice exhibited greatly reduced Src activity and tyrosine phosphorylation of other synaptic vesicle proteins. Disruption of the Src-synapsin interaction by internalization of either the Src SH3 or SH2 domains into synaptosomes decreased synapsin tyrosine phosphorylation and concomitantly increased neurotransmitter release in response to Ca(2+)-ionophores. We conclude that synapsin is an endogenous substrate and activator of synaptic vesicle-associated c-Src and that regulation of Src activity on synaptic vesicles participates in the regulation of neurotransmitter release by synapsin.
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Affiliation(s)
- Franco Onofri
- Department of Experimental Medicine, University of Genova, 16132 Genova, Italy
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16
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Fassio A, Merlo D, Mapelli J, Menegon A, Corradi A, Mete M, Zappettini S, Bonanno G, Valtorta F, D'Angelo E, Benfenati F. The synapsin domain E accelerates the exoendocytotic cycle of synaptic vesicles in cerebellar Purkinje cells. J Cell Sci 2007; 119:4257-68. [PMID: 17038543 DOI: 10.1242/jcs.03194] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Synapsins are synaptic-vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release and excitability of neuronal networks. Mutation of synapsin genes in mouse and human causes epilepsy. To understand the role of the highly conserved synapsin domain E in the dynamics of release from mammalian inhibitory neurons, we generated mice that selectively overexpress the most conserved part of this domain in cerebellar Purkinje cells. At Purkinje-cell-nuclear-neuron synapses, transgenic mice were more resistant to depression induced by short or prolonged high-frequency stimulations. The increased synaptic performance was accompanied by accelerated release kinetics and shorter synaptic delay. Despite a marked decrease in the total number of synaptic vesicles, vesicles at the active zone were preserved or slightly increased. The data indicate that synapsin domain E increases synaptic efficiency by accelerating both the kinetics of exocytosis and the rate of synaptic vesicle cycling and decreasing depression at the inhibitory Purkinje-cell-nuclear-neuron synapse. These effects may increase the sensitivity of postsynaptic neurons to inhibition and thereby contribute to the inhibitory control of network activity.
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Affiliation(s)
- Anna Fassio
- Center of Neuroscience and Neuroengineering, Department of Experimental Medicine, University of Genoa, Italy
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17
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Shin JH, Guedj F, Delabar JM, Lubec G. Dysregulation of growth factor receptor-bound protein 2 and fascin in hippocampus of mice polytransgenic for chromosome 21 structures. Hippocampus 2007; 17:1180-92. [PMID: 17696169 DOI: 10.1002/hipo.20351] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Nonchimeric polytransgenic 152F7 mice encompassing four human chromosome 21 genes (DSCR3, DSCR5, TTC3, and DYRK1A) within the Down syndrome critical region present with learning and memory impairment. However, no abnormalities were shown by in vitro electrophysiological or neuroanatomical findings in hippocampus of 152F7 mice. To search for molecular changes that may be linked to cognitive impairment, we compared hippocampal protein levels between nontransgenic (WT) and 152F7 mice by a proteomic approach. Protein extracts were run on two-dimensional gel electrophoresis, protein spots were analyzed by mass spectrometry (MALDI-TOF-TOF) followed by quantification by specific software. Three hundred and nineteen different gene products were identified, and 48 proteins were assigned as signaling-related proteins. Stringent statistical analysis considering P < 0.005 as statistically significant based upon multiple testing revealed that growth factor receptor-bound protein 2 (Grb2) levels were decreased and an expression form of fascin 1 was increased in 152F7 mice when compared with WT. A series of proteins showed trends for increased and decreased hippocampal levels (P > 0.005 and P < 0.05). Only 2 out of 319 different gene products were dysregulated, pointing to the specificity of the analysis. Decreased Grb2 levels in the hippocampus of 152F7 mice may contribute to impaired cytoskeleton functions because dynamin 1 binds to Grb2 and involved in the formation of the endocytic process. Fascin dysregulation is of relevance for actin bundling in vesicle trafficking and may represent or lead to impaired neurotransmission that, in turn, may lead to the cognitive defect observed in this mouse model of Down syndrome.
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Affiliation(s)
- Joo-Ho Shin
- Department of Pediatrics, Medical University of Vienna, Vienna, Austria
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18
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Lane-Guermonprez L, Morot-Gaudry-Talarmain Y, Meunier FM, O'Regan S, Onofri F, Le Caer JP, Benfenati F. Synapsin associates with cyclophilin B in an ATP- and cyclosporin A-dependent manner. J Neurochem 2005; 93:1401-11. [PMID: 15935056 DOI: 10.1111/j.1471-4159.2005.03125.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Immunophilins are ubiquitous enzymes responsible for proline isomerisation during protein synthesis and for the chaperoning of several membrane proteins. These activities can be blocked by the immunosuppressants cyclosporin A, FK506 and rapamycin. It has been shown that all three immunosuppressants have neurotrophic activity and can modulate neurotransmitter release, but the molecular basis of these effects is currently unknown. Here, we show that synapsin I, a synaptic vesicle-associated protein, can be purified from Torpedo cholinergic synaptosomes through its affinity to cyclophilin B, an immunophilin that is particularly abundant in brain. The interaction is direct and conserved in mammals, and shows a dissociation constant of about 0.5 microM in vitro. The binding between the two proteins can be disrupted by cyclosporin A and inhibited by physiological concentrations of ATP. Furthermore, cyclophilin B co-localizes with synapsin I in rat synaptic vesicle fractions and its levels in synaptic vesicle-containing fractions are decreased in synapsin knockout mice. These results suggest that immunophilins are involved in the complex protein networks operating at the presynaptic level and implicate the interaction between cyclophilin B and synapsins in presynaptic function.
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Affiliation(s)
- Lydie Lane-Guermonprez
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS UPR 9040, Gif sur Yvette Cedex, France
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19
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Giovedì S, Vaccaro P, Valtorta F, Darchen F, Greengard P, Cesareni G, Benfenati F. Synapsin Is a Novel Rab3 Effector Protein on Small Synaptic Vesicles. J Biol Chem 2004; 279:43760-8. [PMID: 15265865 DOI: 10.1074/jbc.m403293200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Synapsins, a family of neuron-specific phosphoproteins, have been demonstrated to regulate the availability of synaptic vesicles for exocytosis by binding to both synaptic vesicles and the actin cytoskeleton in a phosphorylation-dependent manner. Although the above-mentioned observations strongly support a pre-docking role of the synapsins in the assembly and maintenance of a reserve pool of synaptic vesicles, recent results suggest that the synapsins may also be involved in some later step of exocytosis. In order to investigate additional interactions of the synapsins with nerve terminal proteins, we have employed phage display library technology to select peptide sequences binding with high affinity to synapsin I. Antibodies raised against the peptide YQYIETSMQ (syn21) specifically recognized Rab3A, a synaptic vesicle-specific small G protein implicated in multiple steps of exocytosis. The interaction between synapsin I and Rab3A was confirmed by photoaffinity labeling experiments on purified synaptic vesicles and by the formation of a chemically cross-linked complex between synapsin I and Rab3A in intact nerve terminals. Synapsin I could be effectively co-precipitated from synaptosomal extracts by immobilized recombinant Rab3A in a GTP-dependent fashion. In vitro binding assays using purified proteins confirmed the binding preference of synapsin I for Rab3A-GTP and revealed that the COOH-terminal regions of synapsin I and the Rab3A effector domain are required for the interaction with Rab3A to occur. The data indicate that synapsin I is a novel Rab3 interactor on synaptic vesicles and suggest that the synapsin-Rab3 interaction may participate in the regulation of synaptic vesicle trafficking within the nerve terminals.
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Affiliation(s)
- Silvia Giovedì
- Department of Experimental Medicine, Section of Human Physiology, University of Genova, Via Benedetto XV, 16132, Italy
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20
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Bloom O, Evergren E, Tomilin N, Kjaerulff O, Löw P, Brodin L, Pieribone VA, Greengard P, Shupliakov O. Colocalization of synapsin and actin during synaptic vesicle recycling. J Cell Biol 2003; 161:737-47. [PMID: 12756235 PMCID: PMC2199372 DOI: 10.1083/jcb.200212140] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2002] [Revised: 04/16/2003] [Accepted: 04/16/2003] [Indexed: 01/21/2023] Open
Abstract
It has been hypothesized that in the mature nerve terminal, interactions between synapsin and actin regulate the clustering of synaptic vesicles and the availability of vesicles for release during synaptic activity. Here, we have used immunogold electron microscopy to examine the subcellular localization of actin and synapsin in the giant synapse in lamprey at different states of synaptic activity. In agreement with earlier observations, in synapses at rest, synapsin immunoreactivity was preferentially localized to a portion of the vesicle cluster distal to the active zone. During synaptic activity, however, synapsin was detected in the pool of vesicles proximal to the active zone. In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones. Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster. Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses. Our data suggest that in addition to its known function in clustering of vesicles in the reserve pool, synapsin migrates from the synaptic vesicle cluster and participates in the organization of the actin-rich cytomatrix in the endocytic zone during synaptic activity.
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Affiliation(s)
- Ona Bloom
- The Rockefeller University, New York, NY 10021, USA.
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21
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Spatial and temporal regulation of Ca2+/calmodulin-dependent protein kinase II activity in developing neurons. J Neurosci 2002. [PMID: 12177199 DOI: 10.1523/jneurosci.22-16-07016.2002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We have studied Ca2+/calmodulin-dependent protein kinase II (CaMKII) isoform distribution and activity in embryonic hippocampal neurons developing in culture. We have found a strong correlation between the expression of the alpha subunit of the enzyme and the ability to undergo depolarization-dependent phosphorylation, which in young neurons is limited to the somatodendritic pool of the kinase. The lack of responsiveness of the axons of young alphaCaMKII-positive neurons is not caused by a lower Ca2+ influx but rather by a differential balance between kinase and phosphatase activities in this compartment. After the establishment of synaptic contacts, the presynaptic pool of the kinase displays an increasing level of activity and acquires the parallel ability to phosphorylate synapsin I, which represents one of the major CaMKII presynaptic targets in mature nerve terminals. In contrast, the activity of the postsynaptic pool of the kinase remains constant throughout synaptogenesis. In the presence of a nearly homogeneous subcellular distribution, this highly regionalized regulation of activity may reflect the multifunctional roles of CaMKII in both developing and mature neurons.
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22
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Khuebachova M, Verzillo V, Skrabana R, Ovecka M, Vaccaro P, Panni S, Bradbury A, Novak M. Mapping the C terminal epitope of the Alzheimer's disease specific antibody MN423. J Immunol Methods 2002; 262:205-15. [PMID: 11983234 DOI: 10.1016/s0022-1759(02)00006-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The mapping of monoclonal antibody epitopes is now predominantly carried out using molecular diversity techniques, phage display in particular. However, until very recently, phage display methods have been inappropriate for the analysis of epitopes that require a free carboxy terminus. Here we describe the use of two different techniques to analyze the known C terminal epitope specificity of MN423, a monoclonal antibody specifically staining truncated tau in Alzheimer's brain. Using a lambda phage based C-terminal random peptide library, and an intracellular expression library based on truncated tau, we show that this antibody has an absolute requirement for a glycine at position -3 with respect to the C terminus. Both methods give similar results, and identify other important residues in the binding site. However, affinity analysis of synthetic peptides revealed that the affinity of the antibody for identified tripeptides was far lower than the pentapeptide sequence in the native target, and that this in turn was considerably below the affinity for the native target itself. This suggests that molecular diversity methods may define minimum, but not necessarily complete epitopes. The methods described here have a general application to the analysis of antibody epitopes suspected to be found at the C terminus.
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Affiliation(s)
- M Khuebachova
- Institute of Neuroimmunology, Slovak Academy of Sciences, 842 45, Bratislava, Slovakia
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23
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Boulanger LM, Huh GS, Shatz CJ. Neuronal plasticity and cellular immunity: shared molecular mechanisms. Curr Opin Neurobiol 2001; 11:568-78. [PMID: 11595490 DOI: 10.1016/s0959-4388(00)00251-8] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
It is becoming evident that neurons express an unusual number of molecules that were originally thought to be specific to immune functions. One such molecule, class I major histocompatibility complex, is required in the activity-dependent refinement and plasticity of connections in the developing and adult central nervous system, demonstrating that molecules can perform critical roles in both systems. Recent studies reveal striking parallels between cellular signaling mechanisms in the immune and nervous systems that may provide unexpected insights into the development, function, and diseases of both systems.
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Affiliation(s)
- L M Boulanger
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA 02115, USA.
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24
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Fiumara F, Onofri F, Benfenati F, Montarolo PG, Ghirardi M. Intracellular injection of synapsin I induces neurotransmitter release in C1 neurons of Helix pomatia contacting a wrong target. Neuroscience 2001; 104:271-80. [PMID: 11311549 DOI: 10.1016/s0306-4522(01)00063-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The contact with the postsynaptic target induces structural and functional modifications in the serotonergic cell C1 of Helix pomatia. In previous studies we have found that the presence of a non-physiological target down-regulates the number of presynaptic varicosities formed by cultured C1 neurons and has a strong inhibitory effect on the action potential-evoked Ca(2+) influx and neurotransmitter release at C1 terminals. Since a large body of experimental evidence implicates the synapsins in the development and functional maturation of synaptic connections, we have investigated whether the injection of exogenous synapsin I into the presynaptic neuron C1 could affect the inhibitory effect of the wrong target on neurotransmitter release. C1 neurons were cultured with the wrong target neuron C3 for three to five days and then injected with either dephosphorylated or Ca(2+)/calmodulin-dependent protein kinase II-phosphorylated Cy3-labeled synapsin I. The subcellular distribution of exogenous synapsin I, followed by fluorescence videomicroscopy, revealed that only synapsin I phosphorylated by Ca(2+)/calmodulin-dependent protein kinase II diffused in the cytoplasm and reached the terminal arborizations of the axon, while the dephosphorylated form did not diffuse beyond the cell body. Evoked neurotransmitter release was measured during C1 stimulation using a freshly dissociated neuron B2 (sniffer) micromanipulated in close contact with the terminals of C1. A three-fold increase in the amplitude of the sniffer depolarization with respect to the pre-injection amplitude (190+/-29% increase, n=10, P<0.006) was found 5 min after injection of Ca(2+)/calmodulin-dependent protein kinase II-phosphorylated synapsin I that lasted for about 30 min. No significant change was observed after injection of buffer or dephosphorylated synapsin I. These data indicate that the presence of synapsin I induces a fast increase in neurotransmitter release that overcomes the inhibitory effect of the non-physiological target and suggest that the expression of synapsins may play a role in the modulation of synaptic strength and neural connectivity.
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MESH Headings
- Actins/drug effects
- Actins/metabolism
- Animals
- Calcium-Calmodulin-Dependent Protein Kinases/metabolism
- Carbocyanines/pharmacokinetics
- Cell Communication/drug effects
- Cell Communication/physiology
- Cells, Cultured/cytology
- Cells, Cultured/drug effects
- Cells, Cultured/metabolism
- Fluorescent Antibody Technique
- Ganglia, Invertebrate/cytology
- Ganglia, Invertebrate/growth & development
- Ganglia, Invertebrate/metabolism
- Helix, Snails/cytology
- Helix, Snails/growth & development
- Helix, Snails/metabolism
- Intracellular Fluid/drug effects
- Intracellular Fluid/metabolism
- Models, Animal
- Neural Pathways/drug effects
- Neural Pathways/growth & development
- Neural Pathways/metabolism
- Neurotransmitter Agents/metabolism
- Phosphorylation/drug effects
- Presynaptic Terminals/drug effects
- Presynaptic Terminals/metabolism
- Serotonin/metabolism
- Synapsins/metabolism
- Synapsins/pharmacology
- Synaptic Vesicles/drug effects
- Synaptic Vesicles/metabolism
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Affiliation(s)
- F Fiumara
- Department of Neuroscience, Section of Physiology, University of Torino, Corso Raffaello 30, 10125, Torino, Italy
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Menegon A, Dunlap DD, Castano F, Benfenati F, Czernik AJ, Greengard P, Valtorta F. Use of phosphosynapsin I-specific antibodies for image analysis of signal transduction in single nerve terminals. J Cell Sci 2000; 113 ( Pt 20):3573-82. [PMID: 11017873 DOI: 10.1242/jcs.113.20.3573] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have developed a semi-quantitative method for indirectly revealing variations in the concentration of second messengers (Ca(2+), cyclic AMP) in single presynaptic boutons by detecting the phosphorylation of the synapsins, excellent nerve terminal substrates for cyclic AMP- and Ca(2+)/calmodulin-dependent protein kinases. For this purpose, we employed polyclonal, antipeptide antibodies recognising exclusively synapsin I phosphorylated by Ca(2+)/calmodulin-dependent protein kinase II (at site 3) or synapsins I/II phosphorylated by either cAMP-dependent protein kinase or Ca(2+)/calmodulin-dependent protein kinase I (at site 1). Cerebellar granular neurones in culture were double-labelled with a monoclonal antibody to synapsins I/II and either of the polyclonal antibodies. Digitised images were analysed to determine the relative phosphorylation stoichiometry at each individual nerve terminal. We have found that: (i) under basal conditions, phosphorylation of site 3 was undetectable, whereas site 1 exhibited some degree of constitutive phosphorylation; (ii) depolarisation in the presence of extracellular Ca(2+) was followed by a selective and widespread increase in site 3 phosphorylation, although the relative phosphorylation stoichiometry varied among individual terminals; and (iii) phosphorylation of site 1 was increased by stimulation of cyclic AMP-dependent protein kinase but not by depolarisation and often occurred in specific nerve terminal sub-populations aligned along axon branches. In addition to shedding light on the regulation of synapsin phosphorylation in living nerve terminals, this approach permits the spatially-resolved analysis of the activation of signal transduction pathways in the presynaptic compartment, which is usually too small to be studied with other currently available techniques.
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Affiliation(s)
- A Menegon
- Dept Neuroscience, San Raffaele Scientific Institute, Milan, Italy.
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Onofri F, Giovedi S, Kao HT, Valtorta F, Bongiorno Borbone L, De Camilli P, Greengard P, Benfenati F. Specificity of the binding of synapsin I to Src homology 3 domains. J Biol Chem 2000; 275:29857-67. [PMID: 10899172 DOI: 10.1074/jbc.m006018200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Synapsins are synaptic vesicle-associated phosphoproteins involved in synapse formation and regulation of neurotransmitter release. Recently, synapsin I has been found to bind the Src homology 3 (SH3) domains of Grb2 and c-Src. In this work we have analyzed the interactions between synapsins and an array of SH3 domains belonging to proteins involved in signal transduction, cytoskeleton assembly, or endocytosis. The binding of synapsin I was specific for a subset of SH3 domains. The highest binding was observed with SH3 domains of c-Src, phospholipase C-gamma, p85 subunit of phosphatidylinositol 3-kinase, full-length and NH(2)-terminal Grb2, whereas binding was moderate with the SH3 domains of amphiphysins I/II, Crk, alpha-spectrin, and NADPH oxidase factor p47(phox) and negligible with the SH3 domains of p21(ras) GTPase-activating protein and COOH-terminal Grb2. Distinct sites in the proline-rich COOH-terminal region of synapsin I were found to be involved in binding to the various SH3 domains. Synapsin II also interacted with SH3 domains with a partly distinct binding pattern. Phosphorylation of synapsin I in the COOH-terminal region by Ca(2+)/calmodulin-dependent protein kinase II or mitogen-activated protein kinase modulated the binding to the SH3 domains of amphiphysins I/II, Crk, and alpha-spectrin without affecting the high affinity interactions. The SH3-mediated interaction of synapsin I with amphiphysins affected the ability of synapsin I to interact with actin and synaptic vesicles, and pools of synapsin I and amphiphysin I were shown to associate in isolated nerve terminals. The ability to bind multiple SH3 domains further implicates the synapsins in signal transduction and protein-protein interactions at the nerve terminal level.
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Affiliation(s)
- F Onofri
- Department of Experimental Medicine, Section of Physiology, University of Genova, Via Benedetto XV 3, I-16132 Genova, Italy
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Dearborn RE, Szaro BG, Lnenicka GA. Cloning and characterization of AASPs: novel axon-associated SH3 binding-like proteins. JOURNAL OF NEUROBIOLOGY 1999; 38:581-94. [PMID: 10084691 DOI: 10.1002/(sici)1097-4695(199903)38:4<581::aid-neu12>3.0.co;2-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Two cDNAs encoding closely related proteins were isolated from a crayfish nervous system lambdagtl0 cDNA library with a rat synapsin Ia cDNA probe. These proteins were expressed exclusively in neurons, were highly enriched in axons of the crayfish, and contained multiple, overlapping, putative Src homology 3 (SH3) binding sites. In concert with other proteins containing Src homology domains, SH3 binding proteins are thought to mediate protein-protein interactions in receptor signaling processes and with the cytoskeleton. We have named these proteins axon-associated SH3 binding-like proteins (AASPs). Except for these SH3 binding regions, which are also found in synapsins, AASPs were unlike any proteins in the database. AASPs were differentially expressed among motoneuron populations in crayfish and were found in growing axons and growth cones in culture. Affinity purified polyclonal antibodies to AASP-168 recognized immunoreactive proteins in rat and Xenopus, suggesting that AASPs may be conserved across species. Although the cellular function of AASPs is unclear at this time, they appear to be novel members of a neuron-specific SH3 binding protein family, which includes the synapsins.
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Affiliation(s)
- R E Dearborn
- Neurobiology Research Center, Department of Biological Sciences, University at Albany, State University of New York, 12222, USA
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