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Sheng M, Kim E. The postsynaptic organization of synapses. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a005678. [PMID: 22046028 DOI: 10.1101/cshperspect.a005678] [Citation(s) in RCA: 375] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The postsynaptic side of the synapse is specialized to receive the neurotransmitter signal released from the presynaptic terminal and transduce it into electrical and biochemical changes in the postsynaptic cell. The cardinal functional components of the postsynaptic specialization of excitatory and inhibitory synapses are the ionotropic receptors (ligand-gated channels) for glutamate and γ-aminobutyric acid (GABA), respectively. These receptor channels are concentrated at the postsynaptic membrane and embedded in a dense and rich protein network comprised of anchoring and scaffolding molecules, signaling enzymes, cytoskeletal components, as well as other membrane proteins. Excitatory and inhibitory postsynaptic specializations are quite different in molecular organization. The postsynaptic density of excitatory synapses is especially complex and dynamic in composition and regulation; it contains hundreds of different proteins, many of which are required for cognitive function and implicated in psychiatric illness.
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Affiliation(s)
- Morgan Sheng
- The Department of Neuroscience, Genentech Incorporated, San Francisco, California 94080, USA
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Soto F, Bleckert A, Lewis R, Kang Y, Kerschensteiner D, Craig AM, Wong ROL. Coordinated increase in inhibitory and excitatory synapses onto retinal ganglion cells during development. Neural Dev 2011; 6:31. [PMID: 21864334 PMCID: PMC3179698 DOI: 10.1186/1749-8104-6-31] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Accepted: 08/24/2011] [Indexed: 01/29/2023] Open
Abstract
Background Neuronal output is shaped by a balance of excitation and inhibition. How this balance is attained in the central nervous system during development is not well understood, and is complicated by the fact that, in vivo, GABAergic and glycinergic synaptogenesis precedes that of glutamatergic synapses. Here, we determined the distributions of inhibitory postsynaptic sites on the dendritic arbors of individual neurons, and compared their developmental patterns with that of excitatory postsynaptic sites. We focused on retinal ganglion cells (RGCs), the output neurons of the retina, which receive excitatory input from bipolar cells and inhibitory input from amacrine cells. To visualize and map inhibitory postsynaptic sites, we generated transgenic mice in which RGCs express fluorescently tagged Neuroligin 2 (YFP-NL2) under the control of the Thy1 promoter. By labeling RGC dendrites biolistically in YFP-NL2-expressing retinas, we were able to map the spatial distribution and thus densities of inhibitory postsynaptic sites on the dendritic arbors of individual large-field RGCs across ages. Results We demonstrate that YFP-NL2 is present at inhibitory synapses in the inner plexiform layer by its co-localization with gephyrin, the γ2 subunit of the GABAA receptor and glycine receptors. YFP-NL2 puncta were apposed to the vesicular inhibitory transmitter transporter VGAT but not to CtBP2, a marker of presynaptic ribbons found at bipolar cell terminals. Similar patterns of co-localization with synaptic markers were observed for endogenous NL2. We also verified that expression of YFP-NL2 in the transgenic line did not significantly alter spontaneous inhibitory synaptic transmission onto RGCs. Using these mice, we found that, on average, the density of inhibitory synapses on individual arbors increased gradually until eye opening (postnatal day 15). A small centro-peripheral gradient in density found in mature arbors was apparent at the earliest age we examined (postnatal day 8). Unexpectedly, the adult ratio of inhibitory/excitatory postsynaptic sites was rapidly attained, shortly after glutamatergic synaptogenesis commenced (postnatal day 7). Conclusion Our observations suggest that bipolar and amacrine cell synaptogenesis onto RGCs appear coordinated to rapidly attain a balanced ratio of excitatory and inhibitory synapse densities prior to the onset of visual experience.
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Affiliation(s)
- Florentina Soto
- Department of Biological Structure, University of Washington, 1950 Pacific Ave, Seattle, WA 98195, USA
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Luscher B, Fuchs T, Kilpatrick CL. GABAA receptor trafficking-mediated plasticity of inhibitory synapses. Neuron 2011; 70:385-409. [PMID: 21555068 DOI: 10.1016/j.neuron.2011.03.024] [Citation(s) in RCA: 316] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/30/2011] [Indexed: 12/22/2022]
Abstract
Proper developmental, neural cell-type-specific, and activity-dependent regulation of GABAergic transmission is essential for virtually all aspects of CNS function. The number of GABA(A) receptors in the postsynaptic membrane directly controls the efficacy of GABAergic synaptic transmission. Thus, regulated trafficking of GABA(A) receptors is essential for understanding brain function in both health and disease. Here we summarize recent progress in the understanding of mechanisms that allow dynamic adaptation of cell surface expression and postsynaptic accumulation and function of GABA(A) receptors. This includes activity-dependent and cell-type-specific changes in subunit gene expression, assembly of subunits into receptors, as well as exocytosis, endocytic recycling, diffusion dynamics, and degradation of GABA(A) receptors. In particular, we focus on the roles of receptor-interacting proteins, scaffold proteins, synaptic adhesion proteins, and enzymes that regulate the trafficking and function of receptors and associated proteins. In addition, we review neuropeptide signaling pathways that affect neural excitability through changes in GABA(A)R trafficking.
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Affiliation(s)
- Bernhard Luscher
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
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Sassoè-Pognetto M, Frola E, Pregno G, Briatore F, Patrizi A. Understanding the molecular diversity of GABAergic synapses. Front Cell Neurosci 2011; 5:4. [PMID: 21713106 PMCID: PMC3112311 DOI: 10.3389/fncel.2011.00004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 05/23/2011] [Indexed: 01/17/2023] Open
Abstract
GABAergic synapses exhibit a high degree of subcellular and molecular specialization, which contrasts with their apparent simplicity in ultrastructural appearance. Indeed, when observed in the electron microscope, GABAergic synapses fit in the symmetric, or Gray’s type II category, being characterized by a relatively simple postsynaptic specialization. The inhibitory postsynaptic density cannot be readily isolated, and progress in understanding its molecular composition has lagged behind that of excitatory synapses. However, recent studies have brought significant progress in the identification of new synaptic proteins, revealing an unexpected complexity in the molecular machinery that regulates GABAergic synaptogenesis. In this article, we provide an overview of the molecular diversity of GABAergic synapses, and we consider how synapse specificity may be encoded by selective trans-synaptic interactions between pre- and postsynaptic adhesion molecules and secreted factors that reside in the synaptic cleft. We also discuss the importance of developing cataloguing tools that could be used to decipher the molecular diversity of synapses and to predict alterations of inhibitory transmission in the course of neurological diseases.
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Affiliation(s)
- Marco Sassoè-Pognetto
- Department of Anatomy, Pharmacology and Forensic Medicine, University of Turin Torino, Italy
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55
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Waites CL, Garner CC. Presynaptic function in health and disease. Trends Neurosci 2011; 34:326-37. [PMID: 21596448 DOI: 10.1016/j.tins.2011.03.004] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/14/2011] [Accepted: 03/28/2011] [Indexed: 10/18/2022]
Abstract
Neurons communicate with one another at specialized contact sites called synapses, composed of pre- and postsynaptic compartments. Presynaptic compartments, or 'boutons', signal to the postsynaptic compartment by releasing chemical neurotransmitter in response to incoming electrical impulses. Recent studies link defects in the function of presynaptic boutons to the etiology of several neurodevelopmental and neurodegenerative diseases, including autism, schizophrenia and Alzheimer's disease. In this review, we describe five core functions of presynaptic boutons and the molecules that mediate these functions, focusing on a subset that are linked to human disease. We also discuss potential mechanisms through which the loss or alteration of these specific molecules could lead to defects in synaptic communication, neural circuit function and, ultimately, cognition and behavior.
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Affiliation(s)
- Clarissa L Waites
- Department of Psychiatry and Behavioral Sciences, Nancy Pritzker Laboratory, Stanford University School of Medicine, 1201 Welch Rd. Palo Alto, CA 94304-5485, USA
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Neuroligin-4 is localized to glycinergic postsynapses and regulates inhibition in the retina. Proc Natl Acad Sci U S A 2011; 108:3053-8. [PMID: 21282647 DOI: 10.1073/pnas.1006946108] [Citation(s) in RCA: 157] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neuroligins (NL1-NL4) are postsynaptic adhesion proteins that control the maturation and function of synapses in the central nervous system (CNS). Loss-of-function mutations in NL4 are linked to rare forms of monogenic heritable autism, but its localization and function are unknown. Using the retina as a model system, we show that NL4 is preferentially localized to glycinergic postsynapses and that the loss of NL4 is accompanied by a reduced number of glycine receptors mediating fast glycinergic transmission. Accordingly, NL4-deficient ganglion cells exhibit slower glycinergic miniature postsynaptic currents and subtle alterations in their stimulus-coding efficacy, and inhibition within the NL4-deficient retinal network is altered as assessed by electroretinogram recordings. These data indicate that NL4 shapes network activity and information processing in the retina by modulating glycinergic inhibition. Importantly, NL4 is also targeted to inhibitory synapses in other areas of the CNS, such as the thalamus, colliculi, brainstem, and spinal cord, and forms complexes with the inhibitory postsynapse proteins gephyrin and collybistin in vivo, indicating that NL4 is an important component of glycinergic postsynapses.
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Smith KR, Kittler JT. The cell biology of synaptic inhibition in health and disease. Curr Opin Neurobiol 2010; 20:550-6. [PMID: 20650630 DOI: 10.1016/j.conb.2010.06.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Revised: 06/08/2010] [Accepted: 06/10/2010] [Indexed: 11/24/2022]
Abstract
Fast synaptic inhibition is largely mediated by GABA(A) receptors (GABA(A)Rs), ligand-gated chloride channels that play an essential role in the control of cell and network activity in the brain. Recent work has demonstrated that the delivery, number and stability of GABA(A)Rs at inhibitory synapses play a key role in the dynamic regulation of inhibitory synaptic efficacy and plasticity. The regulatory pathways essential for the fine-tuning of synaptic inhibition have also emerged as key sites of vulnerability during pathological changes in cell excitability in disease states.
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Affiliation(s)
- Katharine R Smith
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
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Banovic D, Khorramshahi O, Owald D, Wichmann C, Riedt T, Fouquet W, Tian R, Sigrist SJ, Aberle H. Drosophila neuroligin 1 promotes growth and postsynaptic differentiation at glutamatergic neuromuscular junctions. Neuron 2010; 66:724-38. [PMID: 20547130 DOI: 10.1016/j.neuron.2010.05.020] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/18/2010] [Indexed: 11/28/2022]
Abstract
Precise apposition of presynaptic and postsynaptic domains is a fundamental property of all neuronal circuits. Experiments in vitro suggest that Neuroligins and Neurexins function as key regulatory proteins in this process. In a genetic screen, we recovered several mutant alleles of Drosophila neuroligin 1 (dnlg1) that cause a severe reduction in bouton numbers at neuromuscular junctions (NMJs). In accord with reduced synapse numbers, these NMJs show reduced synaptic transmission. Moreover, lack of postsynaptic DNlg1 leads to deficits in the accumulation of postsynaptic glutamate receptors, scaffold proteins, and subsynaptic membranes, while increased DNlg1 triggers ectopic postsynaptic differentiation via its cytoplasmic domain. DNlg1 forms discrete clusters adjacent to postsynaptic densities. Formation of these clusters depends on presynaptic Drosophila Neurexin (DNrx). However, DNrx binding is not an absolute requirement for DNlg1 function. Instead, other signaling components are likely involved in DNlg1 transsynaptic functions, with essential interactions organized by the DNlg1 extracellular domain but also by the cytoplasmic domain.
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Affiliation(s)
- Daniel Banovic
- University of Münster, Institute for Neurobiology, Münster, Germany
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Saiepour L, Fuchs C, Patrizi A, Sassoè-Pognetto M, Harvey RJ, Harvey K. Complex role of collybistin and gephyrin in GABAA receptor clustering. J Biol Chem 2010; 285:29623-31. [PMID: 20622020 DOI: 10.1074/jbc.m110.121368] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin and collybistin are key components of GABA(A) receptor (GABA(A)R) clustering. Nonetheless, resolving the molecular interactions between the plethora of GABA(A)R subunits and these clustering proteins is a significant challenge. We report a direct interaction of GABA(A)R α2 and α3 subunit intracellular M3-M4 domain (but not α1, α4, α5, α6, β1-3, or γ1-3) with gephyrin. Curiously, GABA(A)R α2, but not α3, binds to both gephyrin and collybistin using overlapping sites. The reciprocal binding sites on gephyrin for collybistin and GABA(A)R α2 also overlap at the start of the gephyrin E domain. This suggests that although GABA(A)R α3 interacts with gephyrin, GABA(A)R α2, collybistin, and gephyrin form a trimeric complex. In support of this proposal, tri-hybrid interactions between GABA(A)R α2 and collybistin or GABA(A)R α2 and gephyrin are strengthened in the presence of gephyrin or collybistin, respectively. Collybistin and gephyrin also compete for binding to GABA(A)R α2 in co-immunoprecipitation experiments and co-localize in transfected cells in both intracellular and submembrane aggregates. Interestingly, GABA(A)R α2 is capable of "activating " collybistin isoforms harboring the regulatory SH3 domain, enabling targeting of gephyrin to the submembrane aggregates. The GABA(A)R α2-collybistin interaction was disrupted by a pathogenic mutation in the collybistin SH3 domain (p.G55A) that causes X-linked intellectual disability and seizures by disrupting GABA(A)R and gephyrin clustering. Because immunohistochemistry in retina revealed a preferential co-localization of collybistin with α2 subunit containing GABA(A)Rs, but not GlyRs or other GABA(A)R subtypes, we propose that the collybistin-gephyrin complex has an intimate role in the clustering of GABA(A)Rs containing the α2 subunit.
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Affiliation(s)
- Leila Saiepour
- Department of Pharmacology, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom
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Jedlicka P, Hoon M, Papadopoulos T, Vlachos A, Winkels R, Poulopoulos A, Betz H, Deller T, Brose N, Varoqueaux F, Schwarzacher SW. Increased Dentate Gyrus Excitability in Neuroligin-2-Deficient Mice in Vivo. Cereb Cortex 2010; 21:357-67. [DOI: 10.1093/cercor/bhq100] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
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Lui L, Levinson JN, Noël G, Handrigan GR, Richman JM, El-Husseini A, Moukhles H. Synaptic localization of neuroligin 2 in the rodent retina: comparative study with the dystroglycan-containing complex. J Neurosci Res 2010; 88:837-49. [PMID: 19859968 DOI: 10.1002/jnr.22258] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Several recent studies have shown that neuroligin 2 (NL2), a component of the cell adhesion neurexins-neuroligins complex, is localized postsynaptically at hippocampal and other inhibitory synapses throughout the brain. Other studies have shown that components of the dystroglycan complex are also localized at a subset of inhibitory synapses and are coexpressed with NL2 in brain. These data prompted us to undertake a comparative study between the localization of NL2 and the dystroglycan complex in the rodent retina. First, we determined that NL2 mRNA is expressed both in the inner and in the outer nuclear layers. Second, we found that NL2 is localized both in the inner and in the outer synaptic plexiform layers. In the latter, the horseshoe-shaped pattern of NL2 and its extensive colocalization with RIM2, a component of the presynaptic active zone at ribbon synapses, argue that NL2 is localized presynaptically at photoreceptor terminals. Third, comparison of NL2 and the dystroglycan complex distribution patterns reveals that, despite their coexpression in the outer plexiform layer, they are spatially segregated within distinct domains of the photoreceptor terminals, where NL2 is selectively associated with the active zone and the dystroglycan complex is distally distributed in the lateral regions. Finally, we report that the dystroglycan deficiency in the mdx(3cv) mouse does not alter NL2 localization in the outer plexiform layer. These data show that the NL2- and dystroglycan-containing complexes are differentially localized in the presynaptic photoreceptor terminals and suggest that they may serve distinct functions in retina.
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Affiliation(s)
- Leona Lui
- Department of Cellular and Physiological Sciences, Life Sciences Institute, The University of British Columbia, Vancouver, British Columbia, Canada
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Poulopoulos A, Aramuni G, Meyer G, Soykan T, Hoon M, Papadopoulos T, Zhang M, Paarmann I, Fuchs C, Harvey K, Jedlicka P, Schwarzacher SW, Betz H, Harvey RJ, Brose N, Zhang W, Varoqueaux F. Neuroligin 2 Drives Postsynaptic Assembly at Perisomatic Inhibitory Synapses through Gephyrin and Collybistin. Neuron 2009; 63:628-42. [DOI: 10.1016/j.neuron.2009.08.023] [Citation(s) in RCA: 364] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 08/23/2009] [Accepted: 08/24/2009] [Indexed: 11/27/2022]
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