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Wagner S, Lee C, Rojas L, Specht CG, Rhee J, Brose N, Papadopoulos T. The α3 subunit of GABA A receptors promotes formation of inhibitory synapses in the absence of collybistin. J Biol Chem 2021; 296:100709. [PMID: 33901490 PMCID: PMC8141935 DOI: 10.1016/j.jbc.2021.100709] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 04/14/2021] [Accepted: 04/22/2021] [Indexed: 01/03/2023] Open
Abstract
Signaling at nerve cell synapses is a key determinant of proper brain function, and synaptic defects—or synaptopathies—are at the basis of many neurological and psychiatric disorders. Collybistin (CB), a brain-specific guanine nucleotide exchange factor, is essential for the formation of γ-aminobutyric acidergic (GABAergic) postsynapses in defined regions of the mammalian forebrain, including the hippocampus and basolateral amygdala. This process depends on a direct interaction of CB with the scaffolding protein gephyrin, which leads to the redistribution of gephyrin into submembranous clusters at nascent inhibitory synapses. Strikingly, synaptic clustering of gephyrin and GABAA type A receptors (GABAARs) in several brain regions, including the cerebral cortex and certain thalamic areas, is unperturbed in CB-deficient mice, indicating that the formation of a substantial subset of inhibitory postsynapses must be controlled by gephyrin-interacting proteins other than CB. Previous studies indicated that the α3 subunit of GABAARs (GABAAR-α3) binds directly and with high affinity to gephyrin. Here, we provide evidence (i) that a homooligomeric GABAAR-α3A343W mutant induces the formation of submembranous gephyrin clusters independently of CB in COS-7 cells, (ii) that gephyrin clustering is unaltered in the neuronal subpopulations endogenously expressing the GABAAR-α3 in CB-deficient brains, and (iii) that exogenous expression of GABAAR-α3 partially rescues impaired gephyrin clustering in CB-deficient hippocampal neurons. Our results identify an important role of GABAAR-α3 in promoting gephyrin-mediated and CB-independent formation of inhibitory postsynapses.
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Affiliation(s)
- Sven Wagner
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - ChoongKu Lee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Lucia Rojas
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Christian G Specht
- Diseases and Hormones of the Nervous System (DHNS), Inserm U1195, Université Paris-Saclay, Le Kremlin-Bicêtre, France
| | - JeongSeop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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Zhou L, Kiss E, Demmig R, Kirsch J, Nawrotzki RA, Kuhse J. Binding of gephyrin to microtubules is regulated by its phosphorylation at Ser270. Histochem Cell Biol 2021; 156:5-18. [PMID: 33796945 PMCID: PMC8277605 DOI: 10.1007/s00418-021-01973-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2021] [Indexed: 12/23/2022]
Abstract
Gephyrin is a multifunctional scaffolding protein anchoring glycine- and subtypes of GABA type A- receptors at inhibitory postsynaptic membrane specializations by binding to the microtubule (MT) and/or the actin cytoskeleton. However, the conditions under which gephyrin can bind to MTs and its regulation are currently unknown. Here, we demonstrate that during the purification of MTs from rat brain by sedimentation of polymerized tubulin using high-speed centrifugation a fraction of gephyrin was bound to MTs, whereas gephyrin phosphorylated at the CDK5-dependent site Ser270 was detached from MTs and remained in the soluble protein fraction. Moreover, after collybistin fostered phosphorylation at Ser270 the binding of a recombinant gephyrin to MTs was strongly reduced in co-sedimentation assays. Correspondingly, upon substitution of wild-type gephyrin with recombinant gephyrin carrying alanine mutations at putative CDK5 phosphorylation sites the binding of gephyrin to MTs was increased. Furthermore, the analysis of cultured HEK293T and U2OS cells by immunofluorescence-microscopy disclosed a dispersed and punctuated endogenous gephyrin immunoreactivity co-localizing with MTs which was evidently not phosphorylated at Ser270. Thus, our study provides additional evidence for the binding of gephyrin to MTs in brain tissue and in in vitro cell systems. More importantly, our findings indicate that gephyrin-MT binding is restricted to a specific gephyrin fraction and depicts phosphorylation of gephyrin as a regulatory mechanism of this process by showing that soluble gephyrin detached from MTs can be detected specifically with the mAb7a antibody, which recognizes the Ser270 phosphorylated- version of gephyrin.
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Affiliation(s)
- Lin Zhou
- Department of Histology and Embryology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People's Republic of China
| | - Eva Kiss
- Department of Cellular and Molecular Biology, University of Medicine, Pharmacy, Science and Technology "G.E. Palade" of Târgu Mures, Târgu Mures, Romania
| | - Rebecca Demmig
- University of Konstanz, Molecular Genetics, Konstanz, Germany
| | - Joachim Kirsch
- Department of Anatomy and Cell Biology, Institut für Anatomie und Zellbiologie, University of Heidelberg, Lehrstuhl II, Im Neuenheimer Feld 307, 69120, Heidelberg, Germany
| | - Ralph Alexander Nawrotzki
- Department of Anatomy and Cell Biology, Institut für Anatomie und Zellbiologie, University of Heidelberg, Lehrstuhl II, Im Neuenheimer Feld 307, 69120, Heidelberg, Germany
| | - Jochen Kuhse
- Department of Anatomy and Cell Biology, Institut für Anatomie und Zellbiologie, University of Heidelberg, Lehrstuhl II, Im Neuenheimer Feld 307, 69120, Heidelberg, Germany.
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Bai G, Wang Y, Zhang M. Gephyrin-mediated formation of inhibitory postsynaptic density sheet via phase separation. Cell Res 2021; 31:312-325. [PMID: 33139925 PMCID: PMC8027005 DOI: 10.1038/s41422-020-00433-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 10/14/2020] [Indexed: 01/30/2023] Open
Abstract
Inhibitory synapses are also known as symmetric synapses due to their lack of prominent postsynaptic densities (PSDs) under a conventional electron microscope (EM). Recent cryo-EM tomography studies indicated that inhibitory synapses also contain PSDs, albeit with a rather thin sheet-like structure. It is not known how such inhibitory PSD (iPSD) sheet might form. Here, we demonstrate that the key inhibitory synapse scaffold protein gephyrin, when in complex with either glycine or GABAA receptors, spontaneously forms highly condensed molecular assemblies via phase separation both in solution and on supported membrane bilayers. Multivalent and specific interactions between the dimeric E-domain of gephyrin and the glycine/GABAA receptor multimer are essential for the iPSD condensate formation. Gephyrin alone does not form condensates. The linker between the G- and E-domains of gephyrin inhibits the iPSD condensate formation via autoinhibition. Phosphorylation of specific residues in the linker or binding of target proteins such as dynein light chain to the linker domain regulates gephyrin-mediated glycine/GABAA receptor clustering. Thus, analogous to excitatory PSDs, iPSDs are also formed by phase separation-mediated condensation of scaffold protein/neurotransmitter receptor complexes.
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Affiliation(s)
- Guanhua Bai
- grid.24515.370000 0004 1937 1450Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong China
| | - Yu Wang
- grid.24515.370000 0004 1937 1450Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong China
| | - Mingjie Zhang
- grid.24515.370000 0004 1937 1450Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong China ,grid.24515.370000 0004 1937 1450Center of Systems Biology and Human Health, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong China
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4
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Reciprocal stabilization of glycine receptors and gephyrin scaffold proteins at inhibitory synapses. Biophys J 2021; 120:805-817. [PMID: 33539789 DOI: 10.1016/j.bpj.2021.01.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 12/14/2020] [Accepted: 01/13/2021] [Indexed: 02/03/2023] Open
Abstract
Postsynaptic scaffold proteins immobilize neurotransmitter receptors in the synaptic membrane opposite to presynaptic vesicle release sites, thus ensuring efficient synaptic transmission. At inhibitory synapses in the spinal cord, the main scaffold protein gephyrin assembles in dense molecule clusters that provide binding sites for glycine receptors (GlyRs). Gephyrin and GlyRs can also interact outside of synapses, where they form receptor-scaffold complexes. Although several models for the formation of postsynaptic scaffold domains in the presence of receptor-scaffold interactions have been advanced, a clear picture of the coupled dynamics of receptors and scaffold proteins at synapses is lacking. To characterize the GlyR and gephyrin dynamics at inhibitory synapses, we performed fluorescence time-lapse imaging after photoconversion to directly visualize the exchange kinetics of recombinant Dendra2-gephyrin in cultured spinal cord neurons. Immuno-immobilization of endogenous GlyRs with specific antibodies abolished their lateral diffusion in the plasma membrane, as judged by the lack of fluorescence recovery after photobleaching. Moreover, the cross-linking of GlyRs significantly reduced the exchange of Dendra2-gephyrin compared with control conditions, suggesting that the kinetics of the synaptic gephyrin pool is strongly dependent on GlyR-gephyrin interactions. We did not observe any change in the total synaptic gephyrin levels after GlyR cross-linking, however, indicating that the number of gephyrin molecules at synapses is not primarily dependent on the exchange of GlyR-gephyrin complexes. We further show that our experimental data can be quantitatively accounted for by a model of receptor-scaffold dynamics that includes a tightly interacting receptor-scaffold domain, as well as more loosely bound receptor and scaffold populations that exchange with extrasynaptic pools. The model can make predictions for single-molecule data such as typical dwell times of synaptic proteins. Taken together, our data demonstrate the reciprocal stabilization of GlyRs and gephyrin at inhibitory synapses and provide a quantitative understanding of their dynamic organization.
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Aubrey KR, Sheipouri D, Balle T, Vandenberg RJ, Otsu Y. Glutamate, d-(-)-2-Amino-5-Phosphonopentanoic Acid, and N-Methyl-d-Aspartate Do Not Directly Modulate Glycine Receptors. Mol Pharmacol 2020; 98:719-729. [PMID: 33051383 DOI: 10.1124/molpharm.120.000127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 09/03/2020] [Indexed: 11/22/2022] Open
Abstract
Replication studies play an essential role in corroborating research findings and ensuring that subsequent experimental works are interpreted correctly. A previously published paper indicated that the neurotransmitter glutamate, along with the compounds N-methyl-d-aspartate (NMDA) and d-(-)-2-amino-5-phosphonopentanoic acid (AP5), acts as positive allosteric modulators of inhibitory glycine receptors. The paper further suggested that this form of modulation would play a role in setting the spinal inhibitory tone and influencing sensory signaling, as spillover of glutamate onto nearby glycinergic synapses would permit rapid crosstalk between excitatory and inhibitory synapses. Here, we attempted to replicate this finding in primary cultured spinal cord neurons, spinal cord slice, and Xenopus laevis oocytes expressing recombinant human glycine receptors. Despite extensive efforts, we were unable to reproduce the finding that glutamate, AP5, and NMDA positively modulate glycine receptor currents. We paid careful attention to critical aspects of the original study design and took into account receptor saturation and protocol deviations such as animal species. Finally, we explored possible explanations for the experimental discrepancy. We found that solution contamination with a high-affinity modulator such as zinc is most likely to account for the error, and we suggest methods for preventing this kind of misinterpretation in future studies aimed at characterizing high-affinity modulators of the glycine receptor. SIGNIFICANCE STATEMENT: A previous study indicates that glutamate spillover onto inhibitory synapses can directly interact with glycine receptors to enhance inhibitory signalling. This finding has important implications for baseline spinal transmission and may play a role when chronic pain develops. However, we failed to replicate the results and did not observe glutamate, d-(-)-2-amino-5-phosphonopentanoic acid, or N-methyl-d-aspartate modulation of native or recombinant glycine receptors. We ruled out various sources for the discrepancy and found that the most likely cause is solution contamination.
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Affiliation(s)
- Karin R Aubrey
- Pain Management Research Institute (K.R.A., Y.O.), Kolling Institute of Medical Research, Royal North Shore Hospital and Northern Clinical School, Faculty of Medicine and Health (K.R.A., Y.O.), Pharmacology, Faculty of Medicine and Health (D.S., R.J.V.), Sydney Pharmacy School, Faculty of Medicine and Health (T.B.), and Brain and Mind Centre (T.B.), The University of Sydney, Sydney, Australia
| | - Diba Sheipouri
- Pain Management Research Institute (K.R.A., Y.O.), Kolling Institute of Medical Research, Royal North Shore Hospital and Northern Clinical School, Faculty of Medicine and Health (K.R.A., Y.O.), Pharmacology, Faculty of Medicine and Health (D.S., R.J.V.), Sydney Pharmacy School, Faculty of Medicine and Health (T.B.), and Brain and Mind Centre (T.B.), The University of Sydney, Sydney, Australia
| | - Thomas Balle
- Pain Management Research Institute (K.R.A., Y.O.), Kolling Institute of Medical Research, Royal North Shore Hospital and Northern Clinical School, Faculty of Medicine and Health (K.R.A., Y.O.), Pharmacology, Faculty of Medicine and Health (D.S., R.J.V.), Sydney Pharmacy School, Faculty of Medicine and Health (T.B.), and Brain and Mind Centre (T.B.), The University of Sydney, Sydney, Australia
| | - Robert J Vandenberg
- Pain Management Research Institute (K.R.A., Y.O.), Kolling Institute of Medical Research, Royal North Shore Hospital and Northern Clinical School, Faculty of Medicine and Health (K.R.A., Y.O.), Pharmacology, Faculty of Medicine and Health (D.S., R.J.V.), Sydney Pharmacy School, Faculty of Medicine and Health (T.B.), and Brain and Mind Centre (T.B.), The University of Sydney, Sydney, Australia
| | - Yo Otsu
- Pain Management Research Institute (K.R.A., Y.O.), Kolling Institute of Medical Research, Royal North Shore Hospital and Northern Clinical School, Faculty of Medicine and Health (K.R.A., Y.O.), Pharmacology, Faculty of Medicine and Health (D.S., R.J.V.), Sydney Pharmacy School, Faculty of Medicine and Health (T.B.), and Brain and Mind Centre (T.B.), The University of Sydney, Sydney, Australia
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6
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Aubrey KR, Supplisson S. Heterogeneous Signaling at GABA and Glycine Co-releasing Terminals. Front Synaptic Neurosci 2018; 10:40. [PMID: 30524262 PMCID: PMC6232519 DOI: 10.3389/fnsyn.2018.00040] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 10/12/2018] [Indexed: 11/14/2022] Open
Abstract
The corelease of several neurotransmitters from a single synaptic vesicle has been observed at many central synapses. Nevertheless, the signaling synergy offered by cotransmission and the mechanisms that maintain the optimal release and detection of neurotransmitters at mixed synapses remain poorly understood, thus limiting our ability to interpret changes in synaptic signaling and identify molecules important for plasticity. In the brainstem and spinal cord, GABA and glycine cotransmission is facilitated by a shared vesicular transporter VIAAT (also named VGAT), and occurs at many immature inhibitory synapses. As sensory and motor networks mature, GABA/glycine cotransmission is generally replaced by either pure glycinergic or GABAergic transmission, and the functional role for the continued corelease of GABA and glycine is unclear. Whether or not, and how, the GABA/glycine content is balanced in VIAAT-expressing vesicles from the same terminal, and how loading variability effects the strength of inhibitory transmission is not known. Here, we use a combination of loose-patch (LP) and whole-cell (WC) electrophysiology in cultured spinal neurons of GlyT2:eGFP mice to sample miniature inhibitory post synaptic currents (mIPSCs) that originate from individual GABA/glycine co-releasing synapses and develop a modeling approach to illustrate the gradual change in mIPSC phenotypes as glycine replaces GABA in vesicles. As a consistent GABA/glycine balance is predicted if VIAAT has access to both amino-acids, we test whether vesicle exocytosis from a single terminal evokes a homogeneous population of mixed mIPSCs. We recorded mIPSCs from 18 individual synapses and detected glycine-only mIPSCs in 4/18 synapses sampled. The rest (14/18) were co-releasing synapses that had a significant proportion of mixed GABA/glycine mIPSCs with a characteristic biphasic decay. The majority (9/14) of co-releasing synapses did not have a homogenous phenotype, but instead signaled with a combination of mixed and pure mIPSCs, suggesting that there is variability in the loading and/or storage of GABA and glycine at the level of individual vesicles. Our modeling predicts that when glycine replaces GABA in synaptic vesicles, the redistribution between the peak amplitude and charge transfer of mIPSCs acts to maintain the strength of inhibition while increasing the temporal precision of signaling.
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Affiliation(s)
- Karin R Aubrey
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, PSL Université Paris Paris, France.,Neurobiology of Pain Laboratory, Kolling Institute, Royal North Shore Hospital St. Leonards, NSW, Australia.,Pain Management Research Institute, Faculty of Medicine and Health, University of Sydney-Northern Clinical School St. Leonards, NSW, Australia
| | - Stéphane Supplisson
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, PSL Université Paris Paris, France
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Schaefer N, Roemer V, Janzen D, Villmann C. Impaired Glycine Receptor Trafficking in Neurological Diseases. Front Mol Neurosci 2018; 11:291. [PMID: 30186111 PMCID: PMC6110938 DOI: 10.3389/fnmol.2018.00291] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 08/02/2018] [Indexed: 12/21/2022] Open
Abstract
Ionotropic glycine receptors (GlyRs) enable fast synaptic neurotransmission in the adult spinal cord and brainstem. The inhibitory GlyR is a transmembrane glycine-gated chloride channel. The immature GlyR protein undergoes various processing steps, e.g., folding, assembly, and maturation while traveling from the endoplasmic reticulum to and through the Golgi apparatus, where post-translational modifications, e.g., glycosylation occur. The mature receptors are forward transported via microtubules to the cellular surface and inserted into neuronal membranes followed by synaptic clustering. The normal life cycle of a receptor protein includes further processes like internalization, recycling, and degradation. Defects in GlyR life cycle, e.g., impaired protein maturation and degradation have been demonstrated to underlie pathological mechanisms of various neurological diseases. The neurological disorder startle disease is caused by glycinergic dysfunction mainly due to missense mutations in genes encoding GlyR subunits (GLRA1 and GLRB). In vitro studies have shown that most recessive forms of startle disease are associated with impaired receptor biogenesis. Another neurological disease with a phenotype similar to startle disease is a special form of stiff-person syndrome (SPS), which is most probably due to the development of GlyR autoantibodies. Binding of GlyR autoantibodies leads to enhanced receptor internalization. Here we focus on the normal life cycle of GlyRs concentrating on assembly and maturation, receptor trafficking, post-synaptic integration and clustering, and GlyR internalization/recycling/degradation. Furthermore, this review highlights findings on impairment of these processes under disease conditions such as disturbed neuronal ER-Golgi trafficking as the major pathomechanism for recessive forms of human startle disease. In SPS, enhanced receptor internalization upon autoantibody binding to the GlyR has been shown to underlie the human pathology. In addition, we discuss how the existing mouse models of startle disease increased our current knowledge of GlyR trafficking routes and function. This review further illuminates receptor trafficking of GlyR variants originally identified in startle disease patients and explains changes in the life cycle of GlyRs in patients with SPS with respect to structural and functional consequences at the receptor level.
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Affiliation(s)
- Natascha Schaefer
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Vera Roemer
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Dieter Janzen
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Carmen Villmann
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
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Gamlin CR, Yu WQ, Wong ROL, Hoon M. Assembly and maintenance of GABAergic and Glycinergic circuits in the mammalian nervous system. Neural Dev 2018; 13:12. [PMID: 29875009 PMCID: PMC5991458 DOI: 10.1186/s13064-018-0109-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 05/06/2018] [Indexed: 12/19/2022] Open
Abstract
Inhibition in the central nervous systems (CNS) is mediated by two neurotransmitters: gamma-aminobutyric acid (GABA) and glycine. Inhibitory synapses are generally GABAergic or glycinergic, although there are synapses that co-release both neurotransmitter types. Compared to excitatory circuits, much less is known about the cellular and molecular mechanisms that regulate synaptic partner selection and wiring patterns of inhibitory circuits. Recent work, however, has begun to fill this gap in knowledge, providing deeper insight into whether GABAergic and glycinergic circuit assembly and maintenance rely on common or distinct mechanisms. Here we summarize and contrast the developmental mechanisms that regulate the selection of synaptic partners, and that promote the formation, refinement, maturation and maintenance of GABAergic and glycinergic synapses and their respective wiring patterns. We highlight how some parts of the CNS demonstrate developmental changes in the type of inhibitory transmitter or receptor composition at their inhibitory synapses. We also consider how perturbation of the development or maintenance of one type of inhibitory connection affects other inhibitory synapse types in the same circuit. Mechanistic insight into the development and maintenance of GABAergic and glycinergic inputs, and inputs that co-release both these neurotransmitters could help formulate comprehensive therapeutic strategies for treating disorders of synaptic inhibition.
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Affiliation(s)
- Clare R Gamlin
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Wan-Qing Yu
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Rachel O L Wong
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Mrinalini Hoon
- Department of Biological Structure, University of Washington, Seattle, WA, USA. .,Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, WI, USA.
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Bourke AM, Bowen AB, Kennedy MJ. New approaches for solving old problems in neuronal protein trafficking. Mol Cell Neurosci 2018; 91:48-66. [PMID: 29649542 DOI: 10.1016/j.mcn.2018.04.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 04/05/2018] [Accepted: 04/06/2018] [Indexed: 11/16/2022] Open
Abstract
Fundamental cellular properties are determined by the repertoire and abundance of proteins displayed on the cell surface. As such, the trafficking mechanisms for establishing and maintaining the surface proteome must be tightly regulated for cells to respond appropriately to extracellular cues, yet plastic enough to adapt to ever-changing environments. Not only are the identity and abundance of surface proteins critical, but in many cases, their regulated spatial positioning within surface nanodomains can greatly impact their function. In the context of neuronal cell biology, surface levels and positioning of ion channels and neurotransmitter receptors play essential roles in establishing important properties, including cellular excitability and synaptic strength. Here we review our current understanding of the trafficking pathways that control the abundance and localization of proteins important for synaptic function and plasticity, as well as recent technological advances that are allowing the field to investigate protein trafficking with increasing spatiotemporal precision.
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Affiliation(s)
- Ashley M Bourke
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Aaron B Bowen
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Matthew J Kennedy
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States.
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Morais TP, Coelho D, Vaz SH, Sebastião AM, Valente CA. Glycine Receptor Activation Impairs ATP-Induced Calcium Transients in Cultured Cortical Astrocytes. Front Mol Neurosci 2018; 10:444. [PMID: 29386993 PMCID: PMC5776331 DOI: 10.3389/fnmol.2017.00444] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Accepted: 12/20/2017] [Indexed: 12/20/2022] Open
Abstract
In central nervous system, glycine receptor (GlyR) is mostly expressed in the spinal cord and brainstem, but glycinergic transmission related elements have also been identified in the brain. Astrocytes are active elements at the tripartite synapse, being responsible for the maintenance of brain homeostasis and for the fine-tuning of synaptic activity. These cells communicate, spontaneously or in response to a stimulus, by elevations in their cytosolic calcium (calcium transients, Ca2+T) that can be propagated to other cells. How these Ca2+T are negatively modulated is yet poorly understood. In this work, we evaluated GlyR expression and its role on calcium signaling modulation in rat brain astrocytes. We first proved that GlyR, predominantly subunits α2 and β, was expressed in brain astrocytes and its localization was confirmed in the cytoplasm and astrocytic processes by immunohistochemistry assays. Calcium imaging experiments in cultured astrocytes showed that glycine (500 μM), a GlyR agonist, caused a concentration-dependent reduction in ATP-induced Ca2+T, an effect abolished by the GlyR antagonist, strychnine (0.8 μM), as well as by nocodazole (1 μM), known to impair GlyR anchorage to the plasma membrane. This effect was mimicked by activation of GABAAR, another Cl--permeable channel. In summary, we demonstrated that GlyR activation in astrocytes mediates an inhibitory effect upon ATP induced Ca2+T, which most probably involves changes in membrane permeability to Cl- and requires GlyR anchorage at the plasma membrane. GlyR in astrocytes may thus be part of a mechanism to modulate astrocyte-to-neuron communication.
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Affiliation(s)
- Tatiana P. Morais
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - David Coelho
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - Sandra H. Vaz
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - Ana M. Sebastião
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - Cláudia A. Valente
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
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11
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Santos JMLD, Vasconcelos JF, Frota GA, Ribeiro WLC, André WPP, Vieira LDS, Teixeira M, Bevilaqua CML, Monteiro JP. Haemonchus contortus β-tubulin isotype 1 gene F200Y and F167Y SNPs are both selected by ivermectin and oxfendazole treatments with differing impacts on anthelmintic resistance. Vet Parasitol 2017; 248:90-95. [DOI: 10.1016/j.vetpar.2017.11.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 10/13/2017] [Accepted: 11/06/2017] [Indexed: 11/15/2022]
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12
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Alvarez FJ. Gephyrin and the regulation of synaptic strength and dynamics at glycinergic inhibitory synapses. Brain Res Bull 2016; 129:50-65. [PMID: 27612963 DOI: 10.1016/j.brainresbull.2016.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/23/2016] [Accepted: 09/05/2016] [Indexed: 01/23/2023]
Abstract
Glycinergic synapses predominate in brainstem and spinal cord where they modulate motor and sensory processing. Their postsynaptic mechanisms have been considered rather simple because they lack a large variety of glycine receptor isoforms and have relatively simple postsynaptic densities at the ultrastructural level. However, this simplicity is misleading being their postsynaptic regions regulated by a variety of complex mechanisms controlling the efficacy of synaptic inhibition. Early studies suggested that glycinergic inhibitory strength and dynamics depend largely on structural features rather than on molecular complexity. These include regulation of the number of postsynaptic glycine receptors, their localization and the amount of co-localized GABAA receptors and GABA-glycine co-transmission. These properties we now know are under the control of gephyrin. Gephyrin is the first postsynaptic scaffolding protein ever discovered and it was recently found to display a large degree of variation and regulation by splice variants, posttranslational modifications, intracellular trafficking and interactions with the underlying cytoskeleton. Many of these mechanisms are governed by converging excitatory activity and regulate gephyrin oligomerization and receptor binding, the architecture of the postsynaptic density (and by extension the whole synaptic complex), receptor retention and stability. These newly uncovered molecular mechanisms define the size and number of gephyrin postsynaptic regions and the numbers and proportions of glycine and GABAA receptors contained within. All together, they control the emergence of glycinergic synapses of different strength and temporal properties to best match the excitatory drive received by each individual neuron or local dendritic compartment.
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Affiliation(s)
- Francisco J Alvarez
- Department of Physiology, Emory University, Atlanta, GA 30322-3110, United States.
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13
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Ogino K, Hirata H. Defects of the Glycinergic Synapse in Zebrafish. Front Mol Neurosci 2016; 9:50. [PMID: 27445686 PMCID: PMC4925712 DOI: 10.3389/fnmol.2016.00050] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 06/13/2016] [Indexed: 12/26/2022] Open
Abstract
Glycine mediates fast inhibitory synaptic transmission. Physiological importance of the glycinergic synapse is well established in the brainstem and the spinal cord. In humans, the loss of glycinergic function in the spinal cord and brainstem leads to hyperekplexia, which is characterized by an excess startle reflex to sudden acoustic or tactile stimulation. In addition, glycinergic synapses in this region are also involved in the regulation of respiration and locomotion, and in the nociceptive processing. The importance of the glycinergic synapse is conserved across vertebrate species. A teleost fish, the zebrafish, offers several advantages as a vertebrate model for research of glycinergic synapse. Mutagenesis screens in zebrafish have isolated two motor defective mutants that have pathogenic mutations in glycinergic synaptic transmission: bandoneon (beo) and shocked (sho). Beo mutants have a loss-of-function mutation of glycine receptor (GlyR) β-subunit b, alternatively, sho mutant is a glycinergic transporter 1 (GlyT1) defective mutant. These mutants are useful animal models for understanding of glycinergic synaptic transmission and for identification of novel therapeutic agents for human diseases arising from defect in glycinergic transmission, such as hyperekplexia or glycine encephalopathy. Recent advances in techniques for genome editing and for imaging and manipulating of a molecule or a physiological process make zebrafish more attractive model. In this review, we describe the glycinergic defective zebrafish mutants and the technical advances in both forward and reverse genetic approaches as well as in vivo visualization and manipulation approaches for the study of the glycinergic synapse in zebrafish.
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Affiliation(s)
- Kazutoyo Ogino
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University Sagamihara, Japan
| | - Hiromi Hirata
- Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University Sagamihara, Japan
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14
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Ashraf S, Beech RN, Hancock MA, Prichard RK. Ivermectin binds to Haemonchus contortus tubulins and promotes stability of microtubules. Int J Parasitol 2015; 45:647-54. [DOI: 10.1016/j.ijpara.2015.03.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Revised: 03/27/2015] [Accepted: 03/30/2015] [Indexed: 11/16/2022]
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15
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Differential GABAergic and glycinergic inputs of inhibitory interneurons and Purkinje cells to principal cells of the cerebellar nuclei. J Neurosci 2014; 34:9418-31. [PMID: 25009273 DOI: 10.1523/jneurosci.0401-14.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The principal neurons of the cerebellar nuclei (CN), the sole output of the olivo-cerebellar system, receive a massive inhibitory input from Purkinje cells (PCs) of the cerebellar cortex. Morphological evidence suggests that CN principal cells are also contacted by inhibitory interneurons, but the properties of this connection are unknown. Using transgenic, tracing, and immunohistochemical approaches in mice, we show that CN interneurons form a large heterogeneous population with GABA/glycinergic phenotypes, distinct from GABAergic olive-projecting neurons. CN interneurons are found to contact principal output neurons, via glycine receptor (GlyR)-enriched synapses, virtually devoid of the main GABA receptor (GABAR) subunits α1 and γ2. Those clusters account for 5% of the total number of inhibitory receptor clusters on principal neurons. Brief optogenetic stimulations of CN interneurons, through selective expression of channelrhodopsin 2 after viral-mediated transfection of the flexed gene in GlyT2-Cre transgenic mice, evoked fast IPSCs in principal cells. GlyR activation accounted for 15% of interneuron IPSC amplitude, while the remaining current was mediated by activation of GABAR. Surprisingly, small GlyR clusters were also found at PC synapses onto principal CN neurons in addition to α1 and γ2 GABAR subunits. However, GlyR activation was found to account for <3% of the PC inhibitory synaptic currents evoked by electrical stimulation. This work establishes CN glycinergic neurons as a significant source of inhibition to CN principal cells, forming contacts molecularly distinct from, but functionally similar to, Purkinje cell synapses. Their impact on CN output, motor learning, and motor execution deserves further investigation.
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Lévi S, Le Roux N, Eugène E, Poncer JC. Benzodiazepine ligands rapidly influence GABAA receptor diffusion and clustering at hippocampal inhibitory synapses. Neuropharmacology 2014; 88:199-208. [PMID: 24930360 DOI: 10.1016/j.neuropharm.2014.06.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 05/23/2014] [Accepted: 06/02/2014] [Indexed: 11/28/2022]
Abstract
Benzodiazepines (BZDs) are widely used in the treatment of a variety of neurological and psychiatric conditions including anxiety, insomnia and epilepsy. BZDs are thought to act predominantly by affecting the gating of GABAA receptor channels, resulting in enhanced GABA-mediated currents in neurons. However, mutations mimicking the effect of BZDs on GABAAR channel gating have been shown to also impact the membrane dynamics and synaptic anchoring of the receptors. Here, using single molecule tracking combined with electrophysiological recordings, we show that BZD ligands rapidly influence the dynamic behavior of GABAARs in hippocampal neurons. Application of the inverse BZD agonist DMCM rapidly increased the diffusion and reduced the clustering of GABAARs at synapses, resulting in reduced postsynaptic currents. Conversely, the BZD full agonist diazepam had little effect at rest but reduced lateral diffusion and increased synaptic stabilization and clustering of GABAARs upon sustained neuronal activity, resulting in enhanced potency of inhibitory synapses. These effects occurred in the absence of detectable changes in gephyrin clusters, suggesting they did not reflect a rapid dispersion of the synaptic scaffold. Thus, alterations of the diffusion and synaptic anchoring of GABAARs represent a novel, unsuspected mechanism through which BZDs rapidly modulate GABA signaling in central neurons.
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Affiliation(s)
- Sabine Lévi
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France.
| | - Nicolas Le Roux
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France
| | - Emmanuel Eugène
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France
| | - Jean Christophe Poncer
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France.
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17
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Hanus C, Kochen L, Tom Dieck S, Racine V, Sibarita JB, Schuman EM, Ehlers MD. Synaptic control of secretory trafficking in dendrites. Cell Rep 2014; 7:1771-8. [PMID: 24931613 PMCID: PMC5321479 DOI: 10.1016/j.celrep.2014.05.028] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 03/16/2014] [Accepted: 05/14/2014] [Indexed: 11/24/2022] Open
Abstract
Localized signaling in neuronal dendrites requires tight spatial control of membrane composition. Upon initial synthesis, nascent secretory cargo in dendrites exits the endoplasmic reticulum (ER) from local zones of ER complexity that are spatially coupled to post-ER compartments. Although newly synthesized membrane proteins can be processed locally, the mechanisms that control the spatial range of secretory cargo transport in dendritic segments are unknown. Here, we monitored the dynamics of nascent membrane proteins in dendritic post-ER compartments under regimes of low or increased neuronal activity. In response to activity blockade, post-ER carriers are highly mobile and are transported over long distances. Conversely, increasing synaptic activity dramatically restricts the spatial scale of post-ER trafficking along dendrites. This activity-induced confinement of secretory cargo requires site-specific phosphorylation of the kinesin motor KIF17 by Ca2+/calmodulin-dependent protein kinases (CaMK). Thus, the length scales of early secretory trafficking in dendrites are tuned by activity-dependent regulation of microtubule-dependent transport.
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Affiliation(s)
- Cyril Hanus
- Max Planck Institute for Brain Research, Frankfurt 60438, Germany.
| | - Lisa Kochen
- Max Planck Institute for Brain Research, Frankfurt 60438, Germany
| | | | - Victor Racine
- Institute of Molecular & Cell Biology, Agency for Science, Technology and Research, Singapore 138673, Singapore
| | | | - Erin M Schuman
- Max Planck Institute for Brain Research, Frankfurt 60438, Germany
| | - Michael D Ehlers
- Neuroscience Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA 02139, USA.
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Enyedi P, Veres I, Braun G, Czirják G. Tubulin binds to the cytoplasmic loop of TRESK background K⁺ channel in vitro. PLoS One 2014; 9:e97854. [PMID: 24830385 PMCID: PMC4022642 DOI: 10.1371/journal.pone.0097854] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 04/25/2014] [Indexed: 12/02/2022] Open
Abstract
The cytoplasmic loop between the second and third transmembrane segments is pivotal in the regulation of TRESK (TWIK-related spinal cord K+ channel, K2P18.1, KCNK18). Calcineurin binds to this region and activates the channel by dephosphorylation in response to the calcium signal. Phosphorylation-dependent anchorage of 14-3-3 adaptor protein also modulates TRESK at this location. In the present study, we identified molecular interacting partners of the intracellular loop. By an affinity chromatography approach using the cytoplasmic loop as bait, we have verified the specific association of calcineurin and 14-3-3 to the channel. In addition to these known interacting proteins, we observed substantial binding of tubulin to the intracellular loop. Successive truncation of the polypeptide and pull-down experiments from mouse brain cytosol narrowed down the region sufficient for the binding of tubulin to a 16 amino acid sequence: LVLGRLSYSIISNLDE. The first six residues of this sequence are similar to the previously reported tubulin-binding region of P2X2 purinergic receptor. The tubulin-binding site of TRESK is located close to the protein kinase A (PKA)-dependent 14-3-3-docking motif of the channel. We provide experimental evidence suggesting that 14-3-3 competes with tubulin for the binding to the cytoplasmic loop of TRESK. It is intriguing that the 16 amino acid tubulin-binding sequence includes the serines, which were previously shown to be phosphorylated by microtubule-affinity regulating kinases (MARK kinases) and contribute to channel inhibition. Although tubulin binds to TRESK in vitro, it remains to be established whether the two proteins also interact in the living cell.
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Affiliation(s)
- Péter Enyedi
- Department of Physiology, Semmelweis University, Budapest, Hungary
| | - Irén Veres
- Department of Physiology, Semmelweis University, Budapest, Hungary
| | - Gabriella Braun
- Department of Physiology, Semmelweis University, Budapest, Hungary
| | - Gábor Czirják
- Department of Physiology, Semmelweis University, Budapest, Hungary
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19
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Abstract
The neurotransmitters GABA and glycine mediate fast synaptic inhibition by activating ligand-gated chloride channels--namely, type A GABA (GABA(A)) and glycine receptors. Both types of receptors are anchored postsynaptically by gephyrin, which self-assembles into a scaffold and interacts with the cytoskeleton. Current research indicates that postsynaptic gephyrin clusters are dynamic assemblies that are held together and regulated by multiple protein-protein interactions. Moreover, post-translational modifications of gephyrin regulate the formation and plasticity of GABAergic synapses by altering the clustering properties of postsynaptic scaffolds and thereby the availability and function of receptors and other signalling molecules. Here, we discuss the formation and regulation of the gephyrin scaffold, its role in GABAergic and glycinergic synaptic function and the implications for the pathophysiology of brain disorders caused by abnormal inhibitory neurotransmission.
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Weltzien F, Puller C, O'Sullivan GA, Paarmann I, Betz H. Distribution of the glycine receptor β-subunit in the mouse CNS as revealed by a novel monoclonal antibody. J Comp Neurol 2013; 520:3962-81. [PMID: 22592841 DOI: 10.1002/cne.23139] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Inhibitory glycine receptors (GlyRs) are composed of homologous α- (α1-4) and β-subunits. The β-subunits (GlyRβ) interact via their large cytosolic loops with the postsynaptic scaffolding protein gephyrin and are therefore considered essential for synaptic localization. In situ hybridization studies indicate a widespread distribution of GlyRβ transcripts throughout the mammalian central nervous system (CNS), whereas GlyRα mRNAs and proteins display more restricted expression patterns. Here we report the generation of a monoclonal antibody that specifically recognizes rodent GlyRβ (mAb-GlyRβ) and does not exhibit crossreactivity with any of the GlyRα1-4 subunits. Immunostaining with this antibody revealed high densities of punctate GlyRβ immunoreactivity at inhibitory synapses in mouse spinal cord, brainstem, midbrain, and olfactory bulb but not in the neocortex, cerebellum, or hippocampus. This contrasts the abundance of GlyRβ transcripts in all major regions of the rodent brain and suggests that GlyRβ protein levels are regulated posttranscriptionally. When mAb-GlyRβ was used in double-labeling experiments with GlyRα1-, α2-, α3-, or α4-specific antibodies to examine the colocalization of GlyRβ with these GlyR subunits in the mouse retina, >90% of the GlyRα1-3 clusters detected were found to be GlyRβ-immunoreactive. A subset (about 50%) of the GlyRα4 puncta in the inner plexiform layer, however, was found to lack GlyRβ and gephyrin immunostaining. These GlyRα4-only clusters were apposed to bassoon immunoreactivity and hence synaptically localized. Their existence points to a gephyrin-independent synaptic localization mechanism for a minor subset of GlyRs.
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Affiliation(s)
- Felix Weltzien
- Department of Neurochemistry, Max-Planck Institute for Brain Research, 60528 Frankfurt, Germany
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Tattikota SG, Sury MD, Rathjen T, Wessels HH, Pandey AK, You X, Becker C, Chen W, Selbach M, Poy MN. Argonaute2 regulates the pancreatic β-cell secretome. Mol Cell Proteomics 2013; 12:1214-25. [PMID: 23358505 DOI: 10.1074/mcp.m112.024786] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Argonaute2 (Ago2) is an established component of the microRNA-induced silencing complex. Similar to miR-375 loss-of-function studies, inhibition of Ago2 in the pancreatic β-cell resulted in enhanced insulin release underlining the relationship between these two genes. Moreover, as the most abundant microRNA in pancreatic endocrine cells, miR-375 was also observed to be enriched in Ago2-associated complexes. Both Ago2 and miR-375 regulate the pancreatic β-cell secretome, and by using quantitative mass spectrometry, we identified the enhanced release of a set of proteins or secretion "signatures " in response to a glucose stimulus using the murine β-cell line MIN6. In addition, the loss of Ago2 resulted in the increased expression of miR-375 target genes, including gephyrin and ywhaz. These targets positively contribute to exocytosis indicating they may mediate the functional role of both miR-375 and Ago proteins in the pancreatic β-cell by influencing the secretory pathway. This study specifically addresses the role of Ago2 in the systemic release of proteins from β-cells and highlights the contribution of the microRNA pathway to the function of this cell type.
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Affiliation(s)
- Sudhir G Tattikota
- Max Delbrueck Center for Molecular Medicine, Robert Rössle Strasse 10, 13125 Berlin, Germany
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22
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Fritschy JM, Panzanelli P, Tyagarajan SK. Molecular and functional heterogeneity of GABAergic synapses. Cell Mol Life Sci 2012; 69:2485-99. [PMID: 22314501 PMCID: PMC11115047 DOI: 10.1007/s00018-012-0926-4] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2011] [Revised: 01/16/2012] [Accepted: 01/19/2012] [Indexed: 01/07/2023]
Abstract
Knowledge of the functional organization of the GABAergic system, the main inhibitory neurotransmitter system, in the CNS has increased remarkably in recent years. In particular, substantial progress has been made in elucidating the molecular mechanisms underlying the formation and plasticity of GABAergic synapses. Evidence available ascribes a key role to the cytoplasmic protein gephyrin to form a postsynaptic scaffold anchoring GABA(A) receptors along with other transmembrane proteins and signaling molecules in the postsynaptic density. However, the mechanisms of gephyrin scaffolding remain elusive, notably because gephyrin can auto-aggregate spontaneously and lacks PDZ protein interaction domains found in a majority of scaffolding proteins. In addition, the structural diversity of GABA(A) receptors, which are pentameric channels encoded by a large family of subunits, has been largely overlooked in these studies. Finally, the role of the dystrophin-glycoprotein complex, present in a subset of GABAergic synapses in cortical structures, remains ill-defined. In this review, we discuss recent results derived mainly from the analysis of mutant mice lacking a specific GABA(A) receptor subtype or a core protein of the GABAergic postsynaptic density (neuroligin-2, collybistin), highlighting the molecular diversity of GABAergic synapses and its relevance for brain plasticity and function. In addition, we discuss the contribution of the dystrophin-glycoprotein complex to the molecular and functional heterogeneity of GABAergic synapses.
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Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, Switzerland.
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Tretter V, Mukherjee J, Maric HM, Schindelin H, Sieghart W, Moss SJ. Gephyrin, the enigmatic organizer at GABAergic synapses. Front Cell Neurosci 2012; 6:23. [PMID: 22615685 PMCID: PMC3351755 DOI: 10.3389/fncel.2012.00023] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2011] [Accepted: 04/23/2012] [Indexed: 11/17/2022] Open
Abstract
GABAA receptors are clustered at synaptic sites to achieve a high density of postsynaptic receptors opposite the input axonal terminals. This allows for an efficient propagation of GABA mediated signals, which mostly result in neuronal inhibition. A key organizer for inhibitory synaptic receptors is the 93 kDa protein gephyrin that forms oligomeric superstructures beneath the synaptic area. Gephyrin has long been known to be directly associated with glycine receptor β subunits that mediate synaptic inhibition in the spinal cord. Recently, synaptic GABAA receptors have also been shown to directly interact with gephyrin and interaction sites have been identified and mapped within the intracellular loops of the GABAA receptor α1, α2, and α3 subunits. Gephyrin-binding to GABAA receptors seems to be at least one order of magnitude weaker than to glycine receptors (GlyRs) and most probably is regulated by phosphorylation. Gephyrin not only has a structural function at synaptic sites, but also plays a crucial role in synaptic dynamics and is a platform for multiple protein-protein interactions, bringing receptors, cytoskeletal proteins and downstream signaling proteins into close spatial proximity.
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Affiliation(s)
- Verena Tretter
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna Vienna, Austria
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24
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Alterations of GABAergic signaling in autism spectrum disorders. Neural Plast 2011; 2011:297153. [PMID: 21766041 PMCID: PMC3134996 DOI: 10.1155/2011/297153] [Citation(s) in RCA: 204] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2011] [Accepted: 04/01/2011] [Indexed: 11/18/2022] Open
Abstract
Autism spectrum disorders (ASDs) comprise a heterogeneous group of pathological conditions, mainly of genetic origin, characterized by stereotyped behavior, marked impairment in verbal and nonverbal communication, social skills, and cognition. Interestingly, in a small number of cases, ASDs are associated with single mutations in genes encoding for neuroligin-neurexin families. These are adhesion molecules which, by regulating transsynaptic signaling, contribute to maintain a proper excitatory/inhibitory (E/I) balance at the network level. Furthermore, GABA, the main inhibitory neurotransmitter in adult life, at late embryonic/early postnatal stages has been shown to depolarize and excite targeted cell through an outwardly directed flux of chloride. The depolarizing action of GABA and associated calcium influx regulate a variety of developmental processes from cell migration and differentiation to synapse formation. Here, we summarize recent data concerning the functional role of GABA in building up and refining neuronal circuits early in development and the molecular mechanisms regulating the E/I balance. A dysfunction of the GABAergic signaling early in development leads to a severe E/I unbalance in neuronal circuits, a condition that may account for some of the behavioral deficits observed in ASD patients.
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Machado P, Rostaing P, Guigonis JM, Renner M, Dumoulin A, Samson M, Vannier C, Triller A. Heat shock cognate protein 70 regulates gephyrin clustering. J Neurosci 2011; 31:3-14. [PMID: 21209184 PMCID: PMC6622739 DOI: 10.1523/jneurosci.2533-10.2011] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/27/2010] [Accepted: 08/02/2010] [Indexed: 11/21/2022] Open
Abstract
Formation and stabilization of postsynaptic glycine receptor (GlyR) clusters result from their association with the polymerized scaffold protein gephyrin. At the cell surface, lateral diffusion and local trapping of GlyR by synaptic gephyrin clusters is one of the main factors controlling their number. However, the mechanisms regulating gephyrin/GlyR cluster sizes are not fully understood. To identify molecular binding partners able to control gephyrin cluster stability, we performed pull-down assays with full-length or truncated gephyrin forms incubated in a rat spinal cord extract, combined with mass spectrometric analysis. We found that heat shock cognate protein 70 (Hsc70), a constitutive member of the heat shock protein 70 (Hsp70) family, selectively binds to the gephyrin G-domain. Immunoelectron microscopy of mouse spinal cord sections showed that Hsc70 could be colocalized with gephyrin at inhibitory synapses. Furthermore, ternary Hsc70-gephyrin-GlyR coclusters were formed following transfection of COS-7 cells. Upon overexpression of Hsc70 in mouse spinal cord neurons, synaptic accumulation of gephyrin was significantly decreased, but GlyR amounts were unaffected. In the same way, Hsc70 inhibition increased gephyrin accumulation at inhibitory synapses without modifying GlyR clustering. Single particle tracking experiments revealed that the increase of gephyrin molecules reduced GlyR diffusion rates without altering GlyR residency at synapses. Our findings demonstrate that Hsc70 regulates gephyrin polymerization independently of its interaction with GlyR. Therefore, gephyrin polymerization and synaptic clustering of GlyR are uncoupled events.
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Affiliation(s)
- Patricia Machado
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Philippe Rostaing
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Jean-Marie Guigonis
- Institut Fédératif de Recherche 50 - Université de Nice-Sophia Antipolis, Faculté de Médecine Pasteur, 06107 Nice, France
| | - Marianne Renner
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Andréa Dumoulin
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Michel Samson
- Institut Fédératif de Recherche 50 - Université de Nice-Sophia Antipolis, Faculté de Médecine Pasteur, 06107 Nice, France
| | - Christian Vannier
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Antoine Triller
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
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Charrier C, Machado P, Tweedie-Cullen RY, Rutishauser D, Mansuy IM, Triller A. A crosstalk between β1 and β3 integrins controls glycine receptor and gephyrin trafficking at synapses. Nat Neurosci 2010; 13:1388-95. [DOI: 10.1038/nn.2645] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Accepted: 08/26/2010] [Indexed: 01/24/2023]
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27
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Waldvogel HJ, Baer K, Eady E, Allen KL, Gilbert RT, Mohler H, Rees MI, Nicholson LFB, Faull RLM. Differential localization of gamma-aminobutyric acid type A and glycine receptor subunits and gephyrin in the human pons, medulla oblongata and uppermost cervical segment of the spinal cord: an immunohistochemical study. J Comp Neurol 2010; 518:305-28. [PMID: 19950251 DOI: 10.1002/cne.22212] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Gephyrin is a multifunctional protein responsible for the clustering of glycine receptors (GlyR) and gamma-aminobutyric acid type A receptors (GABA(A)R). GlyR and GABA(A)R are heteropentameric chloride ion channels that facilitate fast-response, inhibitory neurotransmission in the mammalian brain and spinal cord. We investigated the immunohistochemical distribution of gephyrin and the major GABA(A)R and GlyR subunits in the human light microscopically in the rostral and caudal one-thirds of the pons, in the middle and caudal one-thirds of the medulla oblongata, and in the first cervical segment of the spinal cord. The results demonstrate a widespread pattern of immunoreactivity for GlyR and GABA(A)R subunits throughout these regions, including the spinal trigeminal nucleus, abducens nucleus, facial nucleus, pontine reticular formation, dorsal motor nucleus of the vagus nerve, hypoglossal nucleus, lateral cuneate nucleus, and nucleus of the solitary tract. The GABA(A)R alpha(1) and GlyR alpha(1) and beta subunits show high levels of immunoreactivity in these nuclei. The GABA(A)R subunits alpha(2), alpha(3), beta(2,3), and gamma(2) present weaker levels of immunoreactivity. Exceptions are intense levels of GABA(A)R alpha(2) subunit immunoreactivity in the inferior olivary complex and high levels of GABA(A)R alpha(3) subunit immunoreactivity in the locus coeruleus and raphe nuclei. Gephyrin immunoreactivity is highest in the first segment of the cervical spinal cord and hypoglossal nucleus. Our results suggest that a variety of different inhibitory receptor subtypes is responsible for inhibitory functions in the human brainstem and cervical spinal cord and that gephyrin functions as a clustering molecule for major subtypes of these inhibitory neurotransmitter receptors.
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Affiliation(s)
- H J Waldvogel
- Department of Anatomy with Radiology, Faculty of Medical and Health Science, University of Auckland, Auckland, New Zealand.
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Dumoulin A, Triller A, Kneussel M. Cellular transport and membrane dynamics of the glycine receptor. Front Mol Neurosci 2010; 2:28. [PMID: 20161805 PMCID: PMC2820378 DOI: 10.3389/neuro.02.028.2009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2009] [Accepted: 11/19/2009] [Indexed: 01/04/2023] Open
Abstract
Regulation of synaptic transmission is essential to tune individual-to-network neuronal activity. One way to modulate synaptic strength is to regulate neurotransmitter receptor numbers at postsynaptic sites. This can be achieved either through plasma membrane insertion of receptors derived from intracellular vesicle pools, a process depending on active cytoskeleton transport, or through surface membrane removal via endocytosis. In parallel, lateral diffusion events along the plasma membrane allow the exchange of receptor molecules between synaptic and extrasynaptic compartments, contributing to synaptic strength regulation. In recent years, results obtained from several groups studying glycine receptor (GlyR) trafficking and dynamics shed light on the regulation of synaptic GlyR density. Here, we review (i) proteins and mechanisms involved in GlyR cytoskeletal transport, (ii) the diffusion dynamics of GlyR and of its scaffolding protein gephyrin that control receptor numbers, and its relationship with synaptic plasticity, and (iii) adaptative changes in GlyR diffusion in response to global activity modifications, as a homeostatic mechanism.
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Affiliation(s)
- Andrea Dumoulin
- Biologie Cellulaire de la Synapse, Ecole Normale Superieure Paris, France
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Postsynaptic scaffolding molecules modulate the localization of neuroligins. Neuroscience 2009; 165:782-93. [PMID: 19914352 DOI: 10.1016/j.neuroscience.2009.11.016] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 11/04/2009] [Accepted: 11/05/2009] [Indexed: 11/23/2022]
Abstract
Previous work has shown an important role for neuroligins in promoting the formation of synaptic connections in cultured cells. Although neuroligins enhance both excitatory and inhibitory synapse formation, individual neuroligin isoforms have been shown to preferentially localize to either glutamatergic or GABAergic synapses. Current evidence points to an important role for both the extracellular and intracellular domains of neuroligins in their synaptic localization. Although postsynaptic density protein 95 (PSD-95) has been shown to be involved in the recruitment of neuroligin 1 to excitatory synapses, the localization of neuroligin 2 (NL2) and neuroligin 3 (NL3) to excitatory and inhibitory synapses is less well defined. We assessed the roles of gephyrin and PSD-95, postsynaptic scaffolding molecules exclusively localized to inhibitory and excitatory synapses, respectively, in localizing NL2 and NL3 in primary neuronal cultures. We demonstrate that knockdown of gephyrin results in a significant shift of NL2 from inhibitory to excitatory synaptic contacts, while knockdown of PSD-95 leads to a partial shift of NL2 and NL3 from excitatory to inhibitory contacts. Furthermore, analysis of specific domain deletions within the C-terminal, intracellular domain of NL2 reveals that the region between amino acids 716 and 782 is required for the normal synaptic clustering of this protein. Together, these data suggest that intracellular mechanisms are involved in the targeting of different neuroligin family members to synapses (216).
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Synaptic activation modifies microtubules underlying transport of postsynaptic cargo. Proc Natl Acad Sci U S A 2009; 106:8731-6. [PMID: 19439658 DOI: 10.1073/pnas.0812391106] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptic plasticity, the ability of synapses to change in strength, requires alterations in synaptic molecule compositions over time, and synapses undergo selective modifications on stimulation. Molecular motors operate in sorting/transport of neuronal proteins; however, the targeting mechanisms that guide and direct cargo delivery remain elusive. We addressed the impact of synaptic transmission on the regulation of intracellular microtubule (MT)-based transport. We show that increased neuronal activity, as induced through GlyR activity blockade, facilitates tubulin polyglutamylation, a posttranslational modification thought to represent a molecular traffic sign for transport. Also, GlyR activity blockade alters the binding of the MT-associated protein MAP2 to MTs. By using the kinesin (KIF5) and the postsynaptic protein gephyrin as models, we show that such changes of MT tracks are accompanied by reduced motor protein mobility and cargo delivery into neurites. Notably, the observed neurite targeting deficits are prevented on functional depletion or gene expression knockdown of neuronal polyglutamylase. Our data suggest a previously undescribed concept of synaptic transmission regulating MT-dependent cargo delivery.
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Sekimoto K, Triller A. Compatibility between itinerant synaptic receptors and stable postsynaptic structure. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:031905. [PMID: 19391969 DOI: 10.1103/physreve.79.031905] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Revised: 01/13/2009] [Indexed: 05/27/2023]
Abstract
The density of synaptic receptors in front of presynaptic release sites is stabilized in the presence of scaffold proteins, but the receptors and scaffold molecules have local exchanges with characteristic times shorter than that of the receptor-scaffold assembly. We propose a mesoscopic model to account for the regulation of the local density of receptors as quasiequilibrium. It is based on two zones (synaptic and extrasynaptic) and multilayer (membrane, submembrane, and cytoplasmic) topological organization. The model includes the balance of chemical potentials associated with the receptor and scaffold protein concentrations in the various compartments. The model shows highly cooperative behavior including a "phase change" resulting in the formation of well-defined postsynaptic domains. This study provides theoretical tools to approach the complex issue of synaptic stability at the synapse, where receptors are transiently trapped yet rapidly diffuse laterally on the plasma membrane.
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Affiliation(s)
- Ken Sekimoto
- Laboratoire Matières et Systèmes Complexes, Université Paris Diderot and CNRS-UMR 7057, 10 rue Alice Domont et Léonie Duquet, 75013 Paris, France
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The glycine transporter GlyT2 controls the dynamics of synaptic vesicle refilling in inhibitory spinal cord neurons. J Neurosci 2008; 28:9755-68. [PMID: 18815261 DOI: 10.1523/jneurosci.0509-08.2008] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
At inhibitory synapses, glycine and GABA are accumulated into synaptic vesicles by the same vesicular transporter VGAT/VIAAT (vesicular GABA transporter/vesicular inhibitory amino acid transporter), enabling a continuum of glycine, GABA, and mixed phenotypes. Many fundamental aspects of the presynaptic contribution to the inhibitory phenotypes remain unclear. The neuronal transporter GlyT2 is one of the critical presynaptic factors, because glycinergic transmission is impaired in knock-out GlyT2(-/-) mice and mutations in the human GlyT2 gene slc6a5 are sufficient to cause hyperekplexia. Here, we establish that GlyT2-mediated uptake is directly coupled to the accumulation of glycine into recycling synaptic vesicles using cultured spinal cord neurons derived from GlyT2-enhanced green fluorescent protein transgenic mice. Membrane expression of GlyT2 was confirmed by recording glycine-evoked transporter current. We show that GlyT2 inhibition induces a switch from a predominantly glycine to a predominantly GABA phenotype. This effect was mediated by a reduction of glycinergic quantal size after cytosolic depletion of glycine and was entirely reversed by glycine resupply, illustrating that the filling of empty synaptic vesicles is tightly coupled to GlyT2-mediated uptake. Interestingly, high-frequency trains of stimuli elicit two phases of vesicle release with distinct kinetic requirements for glycine refilling. Thus, our results demonstrate the central role played by GlyT2 in determining inhibitory phenotype and therefore in the physiology and pathology of inhibitory circuits.
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Renner M, Specht CG, Triller A. Molecular dynamics of postsynaptic receptors and scaffold proteins. Curr Opin Neurobiol 2008; 18:532-40. [PMID: 18832033 DOI: 10.1016/j.conb.2008.09.009] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 09/12/2008] [Accepted: 09/15/2008] [Indexed: 11/17/2022]
Abstract
The activity of neurotransmitter receptors determines the strength of synaptic transmission. Therefore, the clustering of receptors at synapses is an important mechanism underlying synaptic plasticity. The dynamic exchange of receptors between synaptic and extrasynaptic membranes is dependent on their interaction with synaptic scaffold proteins. Here, we review the recent advances and emerging concepts related to the dynamics of synaptic proteins at inhibitory and excitatory synapses. These include the imaging techniques that enable the study of protein dynamics in cells, the differences and similarities of receptor dynamics at excitatory and inhibitory synapses, the relationship between the exchange of receptor and scaffold proteins, as well as the role of receptor fluxes in the modulation of synaptic strength.
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Affiliation(s)
- Marianne Renner
- Inserm U789, Biologie Cellulaire de la Synapse, ENS, Paris, France
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Papadopoulos T, Eulenburg V, Reddy-Alla S, Mansuy IM, Li Y, Betz H. Collybistin is required for both the formation and maintenance of GABAergic postsynapses in the hippocampus. Mol Cell Neurosci 2008; 39:161-9. [DOI: 10.1016/j.mcn.2008.06.006] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 05/28/2008] [Accepted: 06/10/2008] [Indexed: 11/16/2022] Open
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Viltono L, Patrizi A, Fritschy JM, Sassoè-Pognetto M. Synaptogenesis in the cerebellar cortex: differential regulation of gephyrin and GABAA receptors at somatic and dendritic synapses of Purkinje cells. J Comp Neurol 2008; 508:579-91. [PMID: 18366064 DOI: 10.1002/cne.21713] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
In rodent cerebellar cortex, synaptogenesis occurs entirely postnatally, allowing study of the mechanisms of synapse formation in vivo. Here we monitored the clustering of GABA(A) receptors and the scaffolding protein gephyrin at GABAergic postsynaptic sites during rat cerebellar development. We found that GABA(A) receptors and gephyrin co-aggregate at nascent synapses in the molecular and Purkinje cell layers with a similar time course. With few exceptions, gephyrin and GABA(A) receptor subunits clustered selectively in front of presynaptic boutons expressing the vesicular inhibitory amino acid transporter VIAAT and no ectopic localization of these molecules was observed. Surprisingly, gephyrin clusters outlining the cell body of Purkinje cells were transient, and disappeared rapidly at the end of the second postnatal week. The loss of gephyrin from perisomatic synapses was coincident with a significant reduction in the size of GABA(A) receptor clusters. Furthermore, these changes were accompanied by a developmental decrease in the size of synaptic appositions, as documented by electron microscopy. These findings suggest that gephyrin takes part in the initial assembly of postsynaptic specializations and reveal an unsuspected heterogeneity in the molecular organization of the postsynaptic apparatus at somatic and dendritic synapses of mature Purkinje cells.
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Affiliation(s)
- Laura Viltono
- Department of Anatomy, Pharmacology and Forensic Medicine, University of Turin, I-10126 Torino, Italy
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37
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Triller A, Choquet D. New Concepts in Synaptic Biology Derived from Single-Molecule Imaging. Neuron 2008; 59:359-74. [DOI: 10.1016/j.neuron.2008.06.022] [Citation(s) in RCA: 213] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 06/20/2008] [Accepted: 06/24/2008] [Indexed: 01/02/2023]
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Gephyrin: where do we stand, where do we go? Trends Neurosci 2008; 31:257-64. [DOI: 10.1016/j.tins.2008.02.006] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 02/17/2008] [Accepted: 02/19/2008] [Indexed: 11/24/2022]
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Muller E, Le Corronc H, Scain AL, Triller A, Legendre P. Despite GABAergic neurotransmission, GABAergic innervation does not compensate for the defect in glycine receptor postsynaptic aggregation in spastic mice. Eur J Neurosci 2008; 27:2529-41. [PMID: 18445051 DOI: 10.1111/j.1460-9568.2008.06217.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the hypoglossal nucleus of wild-type mice, early mixed glycinergic-GABAergic inhibitory transmission becomes mainly glycinergic during postnatal maturation. In spastic mice (SPA), a model of human hyperekplexic syndrome, an insertion into the gene of the glycine receptor (GlyR) beta subunit results in a decreased accumulation of GlyRs at postsynaptic sites and an impaired glycinergic neurotransmission. In SPA mice displaying a mild phenotype (B6C3Fe strain), a compensatory process involving an increased aggregation of GABA(A) receptors (GABA(A)Rs) at postsynaptic sites was proposed to explain survival of mutant animals until adulthood. However, C57BL/6J strain SPA mice which express a lower amount of GlyR beta subunit die 2-3 weeks after birth, suggesting that GABAergic compensation does not necessarily take place. We performed a morphofunctional study of inhibitory synapses in the developing hypoglossal nucleus of C57BL/6J SPA mice. In this mutant, the inhibitory synaptic activity was mainly GABAergic. Accordingly, we observed a developmental loss of glycinergic presynaptic terminals and an increase in the density of GABAergic presynaptic terminals during the first two postnatal weeks. In addition, while C57BL/6J SPA mice displayed a strong impairment in GlyR aggregation at postsynaptic loci, the proportion of inhibitory presynaptic terminals facing diffuse GABA(A)Rs significantly increased during development. Our results suggest crosstalk between postsynaptic and presynaptic elements, leading to the developmental regulation of the presynaptic terminal neurotransmitter content according to the level of postsynaptic GlyR aggregation. They also indicate that GABAergic neurotransmission does not compensate for defects in GlyR postsynaptic aggregation leading to spastic syndrome in C57BL/6J SPA mice.
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Affiliation(s)
- Emilie Muller
- UMR 7102 - Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie, Bat. B, Case 1, 9 Quai Saint Bernard, 75252 Paris CEDEX 05, France
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Muller E, Le-Corronc H, Legendre P. Extrasynaptic and postsynaptic receptors in glycinergic and GABAergic neurotransmission: a division of labor? Front Mol Neurosci 2008; 1:3. [PMID: 18946536 PMCID: PMC2526000 DOI: 10.3389/neuro.02.003.2008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Accepted: 01/30/2008] [Indexed: 01/07/2023] Open
Abstract
Glycine and GABA mediate inhibitory neurotransmission in the spinal cord and central nervous system. The general concept of neurotransmission is now challenged by the contribution of both phasic activation of postsynaptic glycine and GABA(A) receptors (GlyRs and GABA(A)Rs, respectively) and tonic activity of these receptors located at extrasynaptic sites. GlyR and GABA(A)R kinetics depend on several parameters, including subunit composition, subsynaptic localization and activation mode. Postsynaptic and extrasynaptic receptors display different subunit compositions and are activated by fast presynaptic and slow paracrine release of neurotransmitters, respectively. GlyR and GABA(A)R functional properties also rely on their aggregation level, which is higher at postsynaptic densities than at extrasynaptic loci. Finally, these receptors can co-aggregate at mixed inhibitory postsynaptic densities where they cross-modulate their activity, providing another parameter of functional complexity. GlyR and GABA(A)R density at postsynaptic sites results from the balance between their internalization and insertion in the plasma membrane, but also on their lateral diffusion from and to the postsynaptic loci. The dynamic exchange of receptors between synaptic and extrasynaptic sites and their functional adaptation in terms of kinetics point out a new adaptive process of inhibitory neurotransmission.
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Affiliation(s)
- Emilie Muller
- UMR 7102 - Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie Paris, France
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41
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Distinct subcellular distribution of delta-opioid receptor fused with various tags in PC12 cells. Neurochem Res 2008; 33:2028-34. [PMID: 18365312 DOI: 10.1007/s11064-008-9678-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2007] [Accepted: 03/13/2008] [Indexed: 10/22/2022]
Abstract
In small dorsal root ganglion neurons, delta-opioid receptors (DORs) have been found to be mainly distributed in the cytoplasm and often associated with the membrane of large dense-core vesicles (LDCVs) that contain neuropeptides. To study the distribution of DORs under various physiological or pharmacological conditions, the receptors fused with different tags are constructed, transfected into cells or animals, and examined with microscopy. In this study, we show that DOR with different tags have distinct patterns of subcellular distribution in neuroendocrine cells, PC12 cells. Both immunostaining and vesicle fraction analysis showed that the native DORs expressed in PC12 cells were mainly associated with LDCVs. In transfected PC12 cells, DOR tagged with Myc or hemagglutinin exhibited LDCV localization. However, DOR fused with GFP at N- or C-terminus was found to be mainly localized on the cell surface, and mediated the function of DOR agonist. Therefore, the distribution of DOR fused with GFP differs from the native DORs. These results suggest that the subcellular distribution of the receptor could be better presented by the fused tag with smaller molecular size.
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Huang R, He S, Chen Z, Dillon GH, Leidenheimer NJ. Mechanisms of homomeric alpha1 glycine receptor endocytosis. Biochemistry 2007; 46:11484-93. [PMID: 17887775 PMCID: PMC2597333 DOI: 10.1021/bi701093j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Little is known regarding the mechanism(s) by which glycine receptors are endocytosed. Here we examined the endocytosis of homomeric alpha1 glycine receptors expressed in HEK 293 cells using immunofluorescence/confocal microscopy and whole-cell patch-clamp recordings. Our studies demonstrate that constitutive endocytosis of glycine receptors is blocked by the dominant negative dynamin construct K44A and that intracellular dialysis with peptide P4, a dynamin/amphiphysin-disrupting peptide, increased whole-cell glycine-gated chloride currents. To examine whether receptor endocytosis could be regulated by PKC, experiments with the PKC activator PMA (phorbol 12-myristate 13-acetate) were performed. PMA, but not its inactive analogue PMM (phorbol 12-monomyristate), stimulated receptor endocytosis and inhibited glycine-gated chloride currents. Similar to constitutive endocytosis, PKC-stimulated endocytosis was blocked by dynamin K44A. Mutation of a putative AP2 adaptin dileucine motif (L314A, L315A) present in the receptor cytoplasmic loop blocked PMA-stimulated receptor endocytosis and also prevented PMA inhibition of glycine receptor currents. In patch-clamp experiments, intracellular dialysis of a 12-amino acid peptide corresponding to the region of the receptor containing the dileucine motif prevented PKC modulation of wild-type glycine receptors. Unlike PKC modulation of the receptor, constitutive endocytosis was not affected by mutation of this dileucine motif. These results demonstrate that PKC activation stimulates glycine receptor endocytosis, that both constitutive endocytosis and PKC-stimulated endocytosis are dynamin-dependent, and that PKC-stimulated endocytosis, but not constitutive endocytosis, occurs via the dileucine motif (L314A, L315A) within the cytoplasmic loop of the receptor.
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Affiliation(s)
- Renqi Huang
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | - Shaoqing He
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | - Zhenglan Chen
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | - Glenn H. Dillon
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | - Nancy J. Leidenheimer
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130, USA
- To whom correspondence should be addressed: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130. Phone (318) 675-7855. Fax: (318) 675-5180. E-mail:
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Ryzhikov S, Bahr BA. Gephyrin alterations due to protein accumulation stress are reduced by the lysosomal modulator Z-Phe-Ala-diazomethylketone. J Mol Neurosci 2007; 34:131-9. [PMID: 18204977 DOI: 10.1007/s12031-007-9009-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2007] [Accepted: 08/22/2007] [Indexed: 11/25/2022]
Abstract
Inhibitory neurotransmission is important for brain function and requires specific transmitter receptors that are organized in synaptic domains. Gephyrin is a cytoskeletal organization protein that binds tubulin and plays an important role in clustering and organizing select inhibitory neurotransmitter receptors. Here, we tested if gephyrin is altered by protein accumulation stress that is common in age-related neurodegenerative disorders. For this, we used the hippocampal slice model that has been shown to exhibit chloroquine (CQN)-induced protein accumulation, microtubule destabilization, transport failure, and declines in excitatory neurotransmitter receptors and their responses. In addition to the decreases in excitatory receptor subunits and other glutamatergic markers, we found that gephyrin isoforms were reduced across the CQN treatment period. Associated with this decline in gephyrin levels was the production of three gephyrin breakdown products (GBDPs) of 30, 38, and 48 kDa. The induced effects on gephyrin were tested for evidence of recovery through enhancement of lysosomal function that is known to promote protein clearance and microtubule integrity. Using the lysosomal modulator Z-Phe-Ala-diazomethylketone (PADK), gephyrin levels were completely restored in correspondence with the recovery of excitatory glutamatergic components. In addition, GBDPs were significantly reduced after the 2-day PADK treatment, to levels that were at or below those measured in control cultures. These findings suggest that receptor-clustering mechanisms for inhibitory synapses are compromised during protein accumulation events. They also indicate that a lysosomal enhancement strategy can protect gephyrin integrity, which may be vital for the balance between inhibitory and excitatory signaling during age-related diseases.
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Affiliation(s)
- Sophia Ryzhikov
- Department of Pharmaceutical Sciences, University of Connecticut, Storrs, CT 06269, USA
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Bruneau EG, Akaaboune M. Running to stand still: ionotropic receptor dynamics at central and peripheral synapses. Mol Neurobiol 2007; 34:137-51. [PMID: 17220535 DOI: 10.1385/mn:34:2:137] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Revised: 11/30/1999] [Accepted: 06/21/2006] [Indexed: 02/07/2023]
Abstract
For synapses to form and function, neurotransmitter receptors must be recruited to a location on the postsynaptic cell in direct apposition to presynaptic neurotransmitter release. However, once receptors are inserted into the postsynaptic membrane, they are not fixed in place but are continually exchanged between synaptic and extrasynaptic regions, and they cycle between the surface and intracellular compartments. This article highlights and compares the current knowledge about the dynamics of acetylcholine receptors at the vertebrate peripheral neuromuscular junction and AMPA, N-methyl-D-aspartate, and gamma-aminobutyric acid receptors in central synapses.
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Affiliation(s)
- Emile G Bruneau
- Department of Molecular, Cellular and Developmental Biology and Program in Neuroscience, University of Michigan, Ann Arbor, MI, USA
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Moretto Zita M, Marchionni I, Bottos E, Righi M, Del Sal G, Cherubini E, Zacchi P. Post-phosphorylation prolyl isomerisation of gephyrin represents a mechanism to modulate glycine receptors function. EMBO J 2007; 26:1761-71. [PMID: 17347650 PMCID: PMC1847658 DOI: 10.1038/sj.emboj.7601625] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2006] [Accepted: 01/31/2007] [Indexed: 12/24/2022] Open
Abstract
The microtubule binding protein gephyrin plays a prominent role in establishing and maintaining a high concentration of inhibitory glycine receptors juxtaposed to presynaptic releasing sites. Here, we show that endogenous gephyrin undergoes proline-directed phosphorylation, which is followed by the recruitment of the peptidyl-prolyl isomerase Pin1. The interaction between gephyrin and Pin1 is strictly dependent on gephyrin phosphorylation and requires serine-proline consensus sites encompassing the gephyrin proline-rich domain. Upon binding, Pin1 triggers conformational changes in the gephyrin molecule, thus enhancing its ability to bind the beta subunit of GlyRs. Consistently, a downregulation of GlyR clusters was detected in hippocampal neurons derived from Pin1 knockout mice, which was paralleled by a reduction in the amplitude of glycine-evoked currents. Our results suggest that phosphorylation-dependent prolyl isomerisation of gephyrin represents a mechanism for regulating GlyRs function.
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Affiliation(s)
- M Moretto Zita
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
| | - Ivan Marchionni
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
| | - Elisa Bottos
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
| | - Massimo Righi
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
| | - Giannino Del Sal
- Laboratorio Nazionale CIB, AREA Science Park, Trieste, Italy
- Dipartimento di Biochimica Biofisica Chimica delle Macromolecole, Trieste, Italy
| | - Enrico Cherubini
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
| | - Paola Zacchi
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Trieste, Italy
- International School for Advanced Studies, Neuroscience Programme, Area Science Park, Basovizza SS14 Km 163.5, 34012 Trieste, Italy. Tel.: +39 403756510; Fax:+39 403756502; E-mail:
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Ehrensperger MV, Hanus C, Vannier C, Triller A, Dahan M. Multiple association states between glycine receptors and gephyrin identified by SPT analysis. Biophys J 2007; 92:3706-18. [PMID: 17293395 PMCID: PMC1853151 DOI: 10.1529/biophysj.106.095596] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The scaffolding protein gephyrin is known to anchor glycine receptors (GlyR) at synapses and to participate in the dynamic equilibrium between synaptic and extrasynaptic GlyR in the neuronal membrane. Here we investigated the properties of this interaction in cells cotransfected with YFP-tagged gephyrin and GlyR subunits possessing an extracellular myc-tag. In HeLa cells and young neurons, single particle tracking was used to follow in real time individual GlyR, labeled with quantum dots, traveling into and out of gephyrin clusters. Analysis of the diffusion properties of two GlyR subunit types--able or unable to bind gephyrin--gave access to the association states of GlyR with its scaffolding protein. Our results indicated that an important portion of GlyR could be linked to a few molecules of gephyrin outside gephyrin clusters. This emphasizes the role of scaffolding proteins in the extrasynaptic membrane and supports the implication of gephyrin-gephyrin interactions in the stabilization of GlyR at synapses. The kinetic parameters controlling the equilibrium between GlyR inside and outside clusters were also characterized. Within clusters, we identified two subpopulations of GlyR with distinct degrees of stabilization between receptors and scaffolding proteins.
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Affiliation(s)
- Marie-Virginie Ehrensperger
- Laboratoire Kastler Brossel, Centre National de la Recherche Scientifique UMR8552, Ecole normale supérieure, Université Pierre et Marie Curie-Paris 6, 75005 Paris, France
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Saiyed T, Paarmann I, Schmitt B, Haeger S, Sola M, Schmalzing G, Weissenhorn W, Betz H. Molecular Basis of Gephyrin Clustering at Inhibitory Synapses. J Biol Chem 2007; 282:5625-32. [PMID: 17182610 DOI: 10.1074/jbc.m610290200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin is a bifunctional modular protein that, in neurons, clusters glycine receptors and gamma-aminobutyric acid, type A receptors in the postsynaptic membrane of inhibitory synapses. By x-ray crystallography and cross-linking, the N-terminal G-domain of gephyrin has been shown to form trimers and the C-terminal E-domain dimers, respectively. Gephyrin therefore has been proposed to form a hexagonal submembranous lattice onto which inhibitory receptors are anchored. Here, crystal structure-based substitutions at oligomerization interfaces revealed that both G-domain trimerization and E-domain dimerization are essential for the formation of higher order gephyrin oligomers and postsynaptic gephyrin clusters. Insertion of the alternatively spliced C5' cassette into the G-domain inhibited clustering by interfering with trimerization, and mutation of the glycine receptor beta-subunit binding region prevented the localization of the clusters at synaptic sites. Together our findings show that domain interactions mediate gephyrin scaffold formation.
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Affiliation(s)
- Taslimarif Saiyed
- Department of Neurochemistry, Max Planck Institute for Brain Research, Frankfurt, Main, Germany
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Bedet C, Bruusgaard JC, Vergo S, Groth-Pedersen L, Eimer S, Triller A, Vannier C. Regulation of Gephyrin Assembly and Glycine Receptor Synaptic Stability. J Biol Chem 2006; 281:30046-56. [PMID: 16882665 DOI: 10.1074/jbc.m602155200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin is required for the formation of clusters of the glycine receptor (GlyR) in the neuronal postsynaptic membrane. It can make trimers and dimers through its N- and C-terminal G and E domains, respectively. Gephyrin oligomerization could thus create a submembrane lattice providing GlyR-binding sites. We investigated the relationships between the stability of cell surface GlyR and the ability of gephyrin splice variants to form oligomers. Using truncated and full-length gephyrins we found that the 13-amino acid sequence (cassette 5) prevents G domain trimerization. Moreover, E domain dimerization is inhibited by the gephyrin central L domain. All of the gephyrin variants bind GlyR beta subunit cytoplasmic loop with high affinity regardless of their cassette composition. Coexpression experiments in COS-7 cells demonstrated that GlyR bound to gephyrin harboring cassette 5 cannot be stabilized at the cell surface. This gephyrin variant was found to deplete synapses from both GlyR and gephyrin in transfected neurons. These data suggest that the relative expression level of cellular variants influence the overall oligomerization pattern of gephyrin and thus the turnover of synaptic GlyR.
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Affiliation(s)
- Cécile Bedet
- INSERM U789, the Laboratoire de Biologie Cellulaire de la Synapse, Ecole Normale Supérieure, F-75005, Paris, France
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Hanus C, Ehrensperger MV, Triller A. Activity-dependent movements of postsynaptic scaffolds at inhibitory synapses. J Neurosci 2006; 26:4586-95. [PMID: 16641238 PMCID: PMC6674069 DOI: 10.1523/jneurosci.5123-05.2006] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Dendritic spines show an activity-dependent cytoskeleton-based remodeling coupled with variations in receptor number and the functional properties of excitatory synapses. In this study, we analyzed the dynamics of gephyrin containing inhibitory postsynaptic scaffolds imaging a Venus::gephyrin (VeGe) chimera in dissociated spinal cord neurons. We provide evidence that the postsynaptic scaffolds at mature synapses display a submicrometric rapid lateral motion and are continuously moving on the dendritic shaft. This dynamic behavior is calcium dependent and is controlled by the cytoskeleton. Minute rearrangement within the gephyrin scaffold as well as the scaffold lateral displacements are F-actin dependent. The lateral movements are counteracted by microtubules. Moreover, the action of the potassium channel blocker 4-aminopyridine and receptor antagonists indicate that the dynamics of postsynaptic gephyrin scaffolds are controlled by synaptic activity.
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Bausen M, Fuhrmann JC, Betz H, O'sullivan GA. The state of the actin cytoskeleton determines its association with gephyrin: Role of ena/VASP family members. Mol Cell Neurosci 2006; 31:376-86. [PMID: 16376568 DOI: 10.1016/j.mcn.2005.11.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Revised: 10/26/2005] [Accepted: 11/07/2005] [Indexed: 11/16/2022] Open
Abstract
The role the cytoskeleton plays in generating and/or maintaining gephyrin-dependent receptor clusters at inhibitory synapses is poorly understood. Here, the effects of actin cytoskeleton disruption were investigated in eGFP-gephyrin-transfected cells and hippocampal neurons. While gephyrin was not associated with microfilaments in transfected cells, it colocalized with G-actin and cytochalasin-D-induced F-actin patches. The linker region between the MoeA and MogA homology domains of gephyrin was required for colocalization with F-actin patches and for the binding of gephyrin to ena/VASP, an actin anti-capping factor that, in vitro, caused gephyrin binding to polymerized actin. In hippocampal neurons, treatment with cytochalasin D resulted in the redistribution of the neuronal ena/VASP homologue Mena into actin patches and, at early stages of development, a reduction in the number of gephyrin clusters. Our data suggest that Mena binding to F-actin allows for gephyrin recruitment to the leading edge of uncapped actin filaments.
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Affiliation(s)
- Melanie Bausen
- Department of Neurochemistry, Max-Planck Institute for Brain Research, 60528 Frankfurt, Germany
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