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Beneyto M, Meador-Woodruff JH. Lamina-specific abnormalities of NMDA receptor-associated postsynaptic protein transcripts in the prefrontal cortex in schizophrenia and bipolar disorder. Neuropsychopharmacology 2008; 33:2175-86. [PMID: 18033238 DOI: 10.1038/sj.npp.1301604] [Citation(s) in RCA: 198] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The hypothesis of N-methyl-D-aspartate (NMDA) receptor hypofunction in schizophrenia was initially based on observations that blockade of the NMDA subtype of glutamate receptor by noncompetitive antagonists, such as phencyclidine and ketamine, can lead to clinical symptoms similar to those present in schizophrenia. Recently, glutamate has also been implicated in the pathophysiology of the mood disorders. As impaired NMDA receptor activity may be the result of a primary defect in the NMDA receptors themselves, or secondary to dysfunction in the protein complexes that mediate their signaling, we measured expression of both NMDA subunits and associated postsynaptic density (PSD) proteins (PSD95, neurofilament-light (NF-L), and SAP102) transcripts in the dorsolateral prefrontal cortex in subjects with schizophrenia, bipolar disorder, major depression, and a comparison group using tissue from the Stanley Foundation Neuropathology Consortium. We found decreased NR1 expression in all three illnesses, decreased NR2A in schizophrenia and major depression, and decreased NR2C in schizophrenia. We found no changes of NR2B or NR2D. Receptor autoradiography revealed no alterations in receptor binding in any of the illnesses, indicating no change in total receptor number, but taken with the subunit data suggests abnormal receptor stoichiometry. In the same subjects, PSD95 was unchanged in all three illnesses, while reduced NF-L expression was found in schizophrenia, especially in large cells of layer V. SAP102 expression was reduced in bipolar disorder restricted to small cells of layer II and large cells of layer III in bipolar disorder. These alterations likely reflect altered signaling cascades associated with glutamate-mediated neurotransmission within specific cortical circuits in these psychiatric illnesses.
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Affiliation(s)
- Monica Beneyto
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, USA.
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2
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Sun D, Bui BV, Vingrys AJ, Kalloniatis M. Alterations in photoreceptor-bipolar cell signaling following ischemia/reperfusion in the rat retina. J Comp Neurol 2008; 505:131-46. [PMID: 17729268 DOI: 10.1002/cne.21470] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Studies of retinal ischemia/reperfusion indicate a disparity between the anatomical and functional results; while a large number of rod bipolar cells remain postischemia, there is a significant reduction in the amplitude of the scotopic b-wave of the electroretinogram (ERG). We investigated the alterations in photoreceptor-bipolar cell signaling following ischemia/reperfusion and suggest a mechanism for the decrease in b-wave amplitude. A cation channel probe (agmatine, 1-amino-4-guanidobutane, AGB) was used to assess cellular ion channel activity in neurochemically identified cells secondary to endogenous glutamate release or pharmacological manipulations. By applying the "neurochemical truth point" principle (Sun et al. [2007a] J Comp Neurol, this issue), we have been able to confirm the loss of specific subpopulations of neurons. ERG was used to assess gross retinal function, with parameters of the ERG model providing insight into changes in the phototransduction cascade and sensitivity of postreceptoral glutamate receptors. Following ischemia/reperfusion, rod bipolar cells maintained 2-amino-4-phosphonobutyric acid-responsive metabotropic glutamate receptors and displayed no change in sensitivity to flashes of light as assessed by ERG. Therefore, the loss in b-wave amplitude is likely due to alterations in photoreceptoral glutamate release detected as a change in postsynaptic AGB permeation into rod bipolar cells. Bipolar cell to amacrine cell signaling was also altered. The robust AGB entry into cholinergic amacrine cells was virtually absent in retinas that had undergone ischemia/reperfusion but remained in the AII amacrine cells. Such results suggest a loss of glutamate receptors and/or a change in receptor subunit expression in subpopulations of inner retinal neurons. Although many cells retain their characteristic neurochemical labeling following ischemia/reperfusion, caution should be used when assuming cells participate in functional retinal circuits based solely on the persistence of neurochemical labeling.
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Affiliation(s)
- Daniel Sun
- Department of Optometry and Vision Science, University of Auckland, New Zealand
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3
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Coultrap SJ, Nixon KM, Alvestad RM, Valenzuela CF, Browning MD. Differential expression of NMDA receptor subunits and splice variants among the CA1, CA3 and dentate gyrus of the adult rat. ACTA ACUST UNITED AC 2005; 135:104-11. [PMID: 15857673 DOI: 10.1016/j.molbrainres.2004.12.005] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Revised: 11/20/2004] [Accepted: 12/05/2004] [Indexed: 11/26/2022]
Abstract
N-Methyl-d-aspartate (NMDA)-type glutamate receptors in the hippocampus are important mediators of both memory formation and excitotoxicity. It is thought that glutamatergic neurons of the CA1, CA3 and dentate gyrus regions of the hippocampus contribute differentially to memory formation and are differentially sensitive to excitotoxicity. The subunit and/or splice variant composition of the NMDA receptor controls many aspects of receptor function such as ligand affinity, calcium permeability and channel kinetics, as well as interactions with intracellular anchoring and regulatory proteins. Thus, one possible explanation of the differences in NMDA receptor-dependent processes, such as synaptic plasticity and excitotoxicity, among the hippocampal sub-regions is that they differ in subunit and/or splice variant expression. Here we report that the NMDA receptor subunits NR1 and NR2B, along with the four splice variant cassettes of the NR1 subunit are differentially expressed in the CA1, CA3 and dentate gyrus of the hippocampus. Expression of the AMPA receptor subunits GluR1 and GluR2 also differ. These differences may contribute to functional differences, such as with excitotoxicity and synaptic plasticity, that exist between the sub-regions of the hippocampus.
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Affiliation(s)
- Steven J Coultrap
- Department of Pharmacology, University of Colorado at Denver and Health Sciences Center, Mail Stop 8303, PO Box 6511, Aurora, CO 80045-0511, USA.
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4
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Besshoh S, Bawa D, Teves L, Wallace MC, Gurd JW. Increased phosphorylation and redistribution of NMDA receptors between synaptic lipid rafts and post-synaptic densities following transient global ischemia in the rat brain. J Neurochem 2005; 93:186-94. [PMID: 15773918 DOI: 10.1111/j.1471-4159.2004.03009.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Ischemia results in increased phosphorylation of NMDA receptors. To investigate the possible role of lipid rafts in this increase, lipid rafts and post-synaptic densities (PSDs) were isolated by the extraction of rat brain synaptosomes with Triton X-100 followed by sucrose density gradient centrifugation. Lipid rafts accounted for the majority of PSD-95, whereas SAP102 was predominantly located in PSDs. Between 50 and 60% of NMDA receptors were associated with lipid rafts. Greater than 85-90% of Src and Fyn were present in lipid rafts, whereas Pyk2 was mainly associated with PSDs. Lipid rafts and PSDs were isolated from animals subjected to 15 min of global ischemia followed by 6 h of recovery. Ischemia did not affect the yield, density, flotillin-1 or cholesterol content of lipid rafts. Following ischemia, the phosphorylation of NR1 by protein kinase C and tyrosine phosphorylation of NR2A and NR2B was increased in both lipid rafts and PSDs, with a greater increase in tyrosine phosphorylation occurring in the raft fraction. Following ischemia, NR1, NR2A and NR2B levels were elevated in PSDs and reduced in lipid rafts. The findings are consistent with a model involving close interaction between lipid rafts and PSDs and a role for lipid rafts in ischemia-induced signaling pathways.
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Affiliation(s)
- Shintaro Besshoh
- Centre for the Neurobiology of Stress, University of Toronto at Scarborough, Toronto, Canada
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5
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Holmes KD, Mattar P, Marsh DR, Jordan V, Weaver LC, Dekaban GA. The C-terminal C1 cassette of the N -methyl-D-aspartate receptor 1 subunit contains a bi-partite nuclear localization sequence. J Neurochem 2002; 81:1152-65. [PMID: 12068064 DOI: 10.1046/j.1471-4159.2002.00865.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The N -methyl-D-aspartate receptor (NMDAR) is a multimeric transmembrane protein composed of at least two subunits. One subunit, NR1, is derived from a single gene and can be subdivided into three regions: the N-terminal extracellular domain, the transmembrane regions, and the C-terminal intracellular domain. The N-terminal domain is responsible for Mg2+ metal ion binding and channel activity, while the transmembrane domains are important for ion channel formation. The intracellular C-terminal domain is involved in regulating receptor activity and subcellular localization. Our recent experiments indicated that the intracellular C-terminal domain, when expressed independently, localizes almost exclusively in the nucleus. An examination of the amino acid sequence reveals the presence of a putative nuclear localization sequence (NLS) in the C1 cassette of the NR1 intracellular C-terminus. Using an expression vector designed to test whether a putative NLS sequence is a valid, functional NLS, we have demonstrated that a bi-partite NLS does in fact exist within the NR1-1 C-terminus. Computer algorithms identified a putative helix-loop-helix motif that spanned the C0C1 cassettes of the C-terminus. These data suggest that the NR1 subunit may represent another member of a family of transmembrane proteins that undergo intramembrane proteolysis, releasing a cytosolic peptide that is actively translocated to the nucleus leading to alterations in gene regulation.
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Affiliation(s)
- K D Holmes
- The Gene Therapy and Molecular Virology Group and the Neurodegeneration Group, The John P. Robarts Research Institute, London, Ontario, Canada
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6
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Valenti O, Conn PJ, Marino MJ. Distinct physiological roles of the Gq-coupled metabotropic glutamate receptors Co-expressed in the same neuronal populations. J Cell Physiol 2002; 191:125-37. [PMID: 12064455 DOI: 10.1002/jcp.10081] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The group I metabotropic glutamate receptors, mGluR1 and mGluR5, exhibit a high degree of sequence homology, and are often found co-expressed in the same neuronal populations. These receptors couple to a broad array of effector systems, and are implicated in diverse physiological and pathophysiological functions. Due to the high degree of sequence homology, and the findings that these receptors couple identically in recombinant systems, it has been generally assumed that these two group I mGluR subtypes would exhibit redundant function when coexpressed in the same neurons. With the advent of subtype-selective pharmacological tools, it has become possible to tease apart the functions of mGluR1 and mGluR5 in the same neuron. The emerging picture is one of diverse function, which implies differential regulation. Interestingly, the group I mGluRs are modulated by a rich variety of regulatory systems, which may explain how these receptors can mediate divergent actions when present in the same cell.
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Affiliation(s)
- Ornella Valenti
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
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7
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Ly CD, Roche KW, Lee HK, Wenthold RJ. Identification of rat EMAP, a delta-glutamate receptor binding protein. Biochem Biophys Res Commun 2002; 291:85-90. [PMID: 11829466 DOI: 10.1006/bbrc.2002.6413] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
While most subtypes of glutamate receptors have been studied extensively, less is known about the delta-glutamate receptors, delta1 and delta2. Although neither forms functional channels when expressed in heterologous cells, genetic analyses have demonstrated the physiological significance of delta2. We used the cytosolic C-terminus of the delta2 glutamate receptor subunit in a yeast two-hybrid screen of a rat brain cDNA library to identify delta-glutamate receptor binding proteins. We isolated rat EMAP, the rat homolog of a microtubule-associated protein initially isolated and characterized in echinoderms. Rat EMAP contains 10 WD-repeats, which are domains important for mediating protein-protein interactions in a wide variety of proteins. Rat EMAP binds to delta-glutamate receptor subunits within a 50-amino-acid segment of the delta C-terminus. It is widely expressed in both brain and peripheral tissues, including high expression in brainstem and enrichment in the postsynaptic density.
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Affiliation(s)
- C Dune Ly
- Laboratory of Neurochemistry, National Institutes of Health, Bethesda, Maryland 20892, USA
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8
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Holmes KD, Mattar PA, Marsh DR, Weaver LC, Dekaban GA. The N-methyl-D-aspartate receptor splice variant NR1-4 C-terminal domain. Deletion analysis and role in subcellular distribution. J Biol Chem 2002; 277:1457-68. [PMID: 11700309 DOI: 10.1074/jbc.m107809200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The intracellular C-terminal domain of the N-methyl-d-aspartate receptor (NMDAR) subunits 1 (NR1) and 2 (NR2) are important, if not essential, to the process of NMDAR clustering and anchoring at the plasma membrane and the synapse. Eight NR1 splice variants exist, four of which arise from alternative splicing of the C-terminal exon cassettes. Alternative splice variants may display a differential ability to interact with synaptic anchoring proteins, and splicing of C-terminal exon cassettes may alter the mechanism(s) of subcellular localization and targeting. The NR1-4 isoform has a significantly different C-terminal composition than the prototypic NR1-1 isoform. Whereas the NR1-1 C terminus is composed of C0, C1, and C2 exon cassettes, the NR1-4 C terminus is composed of the C0 and C2' cassettes. In the present study, we address the importance of the NR1-4 C-terminal exon cassettes (C0C2') in subcellular localization in differentiated pheochromocytoma (PC12) cells, in organotypic cultures of dorsal root ganglia, and also in heterologous cells. NR1-4-green fluorescent protein chimeras were created with deletion of either C0, C2', or both cassettes to address their importance in subcellular distribution and cell surface expression of the NR1-4 subunit. These experiments demonstrate that the NR1-4 splice variant found predominantly in the spinal cord uses the C0 cassette, to a large degree, to organize the subcellular distribution of this receptor subunit. Although the role of the C2' subunit is less clear, it may be involved in subunit clustering. However, this clustering is not always as efficient as that attributed to C0 alone or to the natural combination of C0C2'. Finally, although an intact C-terminal domain is neither necessary for interaction with the NR2A subunit nor surface expression of the NR1-4 subunit, the C-terminal domain fragment alone blocks surface expression of native NR1-4, in a dominant negative fashion, when the two are coexpressed.
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Affiliation(s)
- Kevin D Holmes
- Gene Therapy and Molecular Virology Group, Department of Microbiology and Immunology, the University of Western Ontario, London, Ontario N6A 5K8, Canada
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9
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El-Husseini AED, Craven SE, Brock SC, Bredt DS. Polarized targeting of peripheral membrane proteins in neurons. J Biol Chem 2001; 276:44984-92. [PMID: 11546762 DOI: 10.1074/jbc.m103049200] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Differential targeting of neuronal proteins to axons and dendrites is essential for directional information flow within the brain, however, little is known about this protein-sorting process. Here, we investigate polarized targeting of lipid-anchored peripheral membrane proteins, postsynaptic density-95 (PSD-95) and growth-associated protein-43 (GAP-43). Whereas the N-terminal palmitoylated motif of PSD-95 is necessary but not sufficient for sorting to dendrites, the palmitoylation motif of GAP-43 is sufficient for axonal targeting and can redirect a PSD-95 chimera to axons. Systematic mutagenesis of the GAP-43 and PSD-95 palmitoylation motifs indicates that the spacing of the palmitoylated cysteines and the presence of nearby basic amino acids determine polarized targeting by these two motifs. Similarly, the axonal protein paralemmin contains a C-terminal palmitoylated domain, which resembles that of GAP-43 and also mediates axonal targeting. These axonally targeted palmitoylation motifs also mediate targeting to detergent-insoluble glycolipid-enriched complexes in heterologous cells, suggesting a possible role for specialized lipid domains in axonal sorting of peripheral membrane proteins.
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Affiliation(s)
- A el-D El-Husseini
- Department of Physiology and Program in Neuroscience, University of California at San Francisco School of Medicine, San Francisco, California 94143, USA
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10
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Roche KW, Standley S, McCallum J, Dune Ly C, Ehlers MD, Wenthold RJ. Molecular determinants of NMDA receptor internalization. Nat Neurosci 2001; 4:794-802. [PMID: 11477425 DOI: 10.1038/90498] [Citation(s) in RCA: 408] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although synaptic AMPA receptors have been shown to rapidly internalize, synaptic NMDA receptors are reported to be static. It is not certain whether NMDA receptor stability at synaptic sites is an inherent property of the receptor, or is due to stabilization by scaffolding proteins. In this study, we demonstrate that NMDA receptors are internalized in both heterologous cells and neurons, and we define an internalization motif, YEKL, on the distal C-terminus of NR2B. In addition, we show that the synaptic protein PSD-95 inhibits NR2B-mediated internalization, and that deletion of the PDZ-binding domain of NR2B increases internalization in neurons. This suggests an involvement for PSD-95 in NMDA receptor regulation and an explanation for NMDA receptor stability at synaptic sites.
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Affiliation(s)
- K W Roche
- Laboratory of Neurochemistry, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Building 36, Room 5B25, Bethesda, Maryland 20892, USA.
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11
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Tomita S, Nicoll RA, Bredt DS. PDZ protein interactions regulating glutamate receptor function and plasticity. J Cell Biol 2001; 153:F19-24. [PMID: 11381098 PMCID: PMC2174328 DOI: 10.1083/jcb.153.5.f19] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Affiliation(s)
- Susumu Tomita
- Department of Physiology, University of California at San Francisco School of Medicine, University of California San Francisco, San Francisco, California 94143-0444
| | - Roger A. Nicoll
- Department of Cellular and Molecular Pharmacology, University of California at San Francisco School of Medicine, University of California San Francisco, San Francisco, California 94143-0444
| | - David S. Bredt
- Department of Physiology, University of California at San Francisco School of Medicine, University of California San Francisco, San Francisco, California 94143-0444
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12
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Misawa H, Kawasaki Y, Mellor J, Sweeney N, Jo K, Nicoll RA, Bredt DS. Contrasting localizations of MALS/LIN-7 PDZ proteins in brain and molecular compensation in knockout mice. J Biol Chem 2001; 276:9264-72. [PMID: 11104771 DOI: 10.1074/jbc.m009334200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteins containing PDZ (postsynaptic density-95, discs large, zonula occludens) domains play a general role in recruiting receptors and enzymes to specific synaptic sites. In Caenorhabditis elegans, a complex of three PDZ proteins, LIN-2/7/10, mediates basolateral targeting of a receptor tyrosine kinase. Homologs of these LIN proteins have also been identified in higher organisms, and here we analyze the MALS/Veli (mammalian LIN-7/vertebrate homolog of LIN-7) proteins in brain. Immunohistochemical staining and in situ hybridization show that MALS occur differentially in discrete populations of neurons throughout the brain. Most neurons express only one MALS protein, although some cells contain two or even all three MALS isoforms. At the subcellular level, MALS proteins are found in both dendritic and axonal locations, suggesting that they may regulate processes at both pre- and postsynaptic sites. Targeted disruption of MALS-1 and MALS-2 does not yield a detectable phenotype, and hippocampal synaptic function and plasticity are intact in the MALS-1/2 double knockouts. Interestingly, MALS-3 protein is dramatically induced in the MALS-1/2 double knockouts, implying that dynamic changes in protein expression may play an important regulatory role for this family of synaptic PDZ proteins.
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Affiliation(s)
- H Misawa
- Department of Physiology and Cellular and Molecular Pharmacology, University of California at San Francisco School of Medicine, San Francisco, California 94143-0444, USA
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13
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Strettoi E, Pignatelli V. Modifications of retinal neurons in a mouse model of retinitis pigmentosa. Proc Natl Acad Sci U S A 2000; 97:11020-5. [PMID: 10995468 PMCID: PMC27141 DOI: 10.1073/pnas.190291097] [Citation(s) in RCA: 233] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Animal models of retinitis pigmentosa include the rd mouse, in which a mutation of a rod-specific phosphodiesterase leads to the rapid loss of photoreceptors during the early postnatal life. Very little is known about changes occurring in inner retinal neurons after photoreceptor loss. These changes are important in view of the possibility of restoring vision in retinas with photoreceptor degeneration by means of cell transplantation or direct stimulation of inner layers. In this paper, we show that bipolar and horizontal cells of the rd mouse retina undergo dramatic morphological modifications accompanying photoreceptor loss, demonstrating a dependence of second order neurons on these cells. While describing modifications of the rd retina, we also provide quantitative information about neurons of the wild-type mouse retina, useful for future studies on genetically altered animals.
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Affiliation(s)
- E Strettoi
- Istituto di Neurofisiologia del Consiglio Nazionale delle Ricerche, Area della Ricerca Consiglio Nazionale delle Ricerche, Via San Cataldo 1, 56100 Pisa, Italy.
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14
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Osten P, Khatri L, Perez JL, Köhr G, Giese G, Daly C, Schulz TW, Wensky A, Lee LM, Ziff EB. Mutagenesis reveals a role for ABP/GRIP binding to GluR2 in synaptic surface accumulation of the AMPA receptor. Neuron 2000; 27:313-25. [PMID: 10985351 DOI: 10.1016/s0896-6273(00)00039-8] [Citation(s) in RCA: 235] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
We studied the role of PDZ proteins GRIP, ABP, and PICK1 in GluR2 AMPA receptor trafficking. An epitope-tagged MycGluR2 subunit, when expressed in hippocampal cultured neurons, was specifically targeted to the synaptic surface. With the mutant MycGluR2delta1-10, which lacks the PDZ binding site, the overall dendritic intracellular transport and the synaptic surface targeting were not affected. However, over time, Myc-GluR2delta1-10 accumulated at synapses significantly less than MycGluR2. Notably, a single residue substitution, S880A, which blocks binding to ABP/GRIP but not to PICK1, reduced synaptic accumulation to the same extent as the PDZ site truncation. We conclude that the association of GluR2 with ABP and/or GRIP but not PICK1 is essential for maintaining the synaptic surface accumulation of the receptor, possibly by limiting its endocytotic rate.
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Affiliation(s)
- P Osten
- Max-Planck Institute for Medical Research, Department of Molecular Neurobiology, Heidelberg, Germany.
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15
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Husi H, Ward MA, Choudhary JS, Blackstock WP, Grant SG. Proteomic analysis of NMDA receptor-adhesion protein signaling complexes. Nat Neurosci 2000; 3:661-9. [PMID: 10862698 DOI: 10.1038/76615] [Citation(s) in RCA: 910] [Impact Index Per Article: 37.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
N-methyl-d-aspartate receptors (NMDAR) mediate long-lasting changes in synapse strength via downstream signaling pathways. We report proteomic characterization with mass spectrometry and immunoblotting of NMDAR multiprotein complexes (NRC) isolated from mouse brain. The NRC comprised 77 proteins organized into receptor, adaptor, signaling, cytoskeletal and novel proteins, of which 30 are implicated from binding studies and another 19 participate in NMDAR signaling. NMDAR and metabotropic glutamate receptor subtypes were linked to cadherins and L1 cell-adhesion molecules in complexes lacking AMPA receptors. These neurotransmitter-adhesion receptor complexes were bound to kinases, phosphatases, GTPase-activating proteins and Ras with effectors including MAPK pathway components. Several proteins were encoded by activity-dependent genes. Genetic or pharmacological interference with 15 NRC proteins impairs learning and with 22 proteins alters synaptic plasticity in rodents. Mutations in three human genes (NF1, Rsk-2, L1) are associated with learning impairments, indicating the NRC also participates in human cognition.
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Affiliation(s)
- H Husi
- Centre for Genome Research, Centre for Neuroscience, University of Edinburgh, West Mains Road, Edinburgh EH9 3JQ, UK
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16
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Lei S, Jackson MF, Jia Z, Roder J, Bai D, Orser BA, MacDonald JF. Cyclic GMP-dependent feedback inhibition of AMPA receptors is independent of PKG. Nat Neurosci 2000; 3:559-65. [PMID: 10816311 DOI: 10.1038/75729] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In central neurons, the second messenger cGMP is believed to induce long-term changes in efficacy at glutamatergic synapses through activation of protein kinase G (PKG). Stimulating nitric oxide synthase, activating soluble guanylyl cyclase or elevating concentrations of intracellular cGMP depressed excitatory synaptic transmission in CA1 hippocampal neurons. Unexpectedly, intracellular cGMP depressed responses of AMPA receptors and inhibited excitatory postsynaptic currents in hippocampal neurons independently of phosphorylation. Our findings demonstrate that cGMP's modulation of excitatory transmission may involve a coupling of AMPA channel activity to levels of cGMP.
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Affiliation(s)
- S Lei
- Departments of Physiology and Pharmacology, University of Toronto, Medical Sciences Bldg., 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada
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17
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Abstract
Target-specific expression of pre- and postsynaptic mechanisms of synaptic transmission has been shown in a variety of central neurons by a number of laboratories. These data have demonstrated that synaptic transmission between single axons diverging onto distinct target neurons can behave independently, differentially influencing activity in the target neuron. Similarly, single neurons are capable of manufacturing molecularly distinct ligand-gated receptors and targeting them to synapses innervated by distinct converging afferent projections. A picture is emerging consistent with a role for both pre- and postsynaptic mechanisms in influencing the target-specific nature of transmission at numerous diverse synapses throughout the mammalian CNS. This target specificity adds another level of complexity in unravelling the roles played by individual neurons within a computational network. To begin to understand the coordinated activity of large ensembles of neurons it is becoming clear that the nature of transmission between individual pre- and postsynaptic elements within a circuit must first be understood for each and every neural element involved.
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Affiliation(s)
- K Tóth
- Laboratory of Cellular and Molecular Neurophysiology, NICHD/NIH, 49 Convent Drive, Bethesda, MD 20892-4995, USA.
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18
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Distinct roles for ionotropic and metabotropic glutamate receptors in the maturation of excitatory synapses. J Neurosci 2000. [PMID: 10704498 DOI: 10.1523/jneurosci.20-06-02229.2000] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We used the single-cell culture preparation to study the role of activity in the development of glutamatergic synapses in vitro. Rat hippocampal cells grown in isolation on glial islands formed functional autaptic connections and continued to elaborate new synapses throughout the 2 week investigation, resulting in increases in both the evoked AMPA receptor (AMPAR) and NMDA receptor (NMDAR) components of the EPSC. Synaptogenesis was not prevented by chronic blockade of sodium channels or all of the known glutamate receptors. Analysis of miniature EPSCs revealed that AMPAR quantal size doubled over time in vitro whereas NMDAR quantal size remained constant. However, the proportion of synaptic responses mediated only by NMDARs increased over time in vitro. The increase in AMPAR quantal size was prevented by TTX and ionotropic glutamate receptor antagonists, whereas the increase in the proportion of NMDAR-only synapses was prevented by metabotropic glutamate receptor antagonists. Notably, chronic NMDAR blockade incubation did not block the formation of the AMPAR EPSC, indicating that NMDAR-dependent plasticity is not necessary for the onset of AMPAR synaptic transmission in this system. We conclude that action potentials and ionotropic glutamate receptor activation are necessary for the developmental increase in AMPAR quantal size and that metabotropic glutamate receptor activation is required for the production of NMDAR-only synapses, but none of these is essential for synapse formation.
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Honjo Y, Nakagawa S, Takeichi M. Blockade of cadherin-6B activity perturbs the distribution of PSD-95 family proteins in retinal neurones. Genes Cells 2000; 5:309-18. [PMID: 10792468 DOI: 10.1046/j.1365-2443.2000.00327.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Synaptic junctions have cadherin-catenin complexes, but their functions are poorly understood. Using retinal neurones, we investigated the role of this adhesion machinery in synaptic organization. RESULTS In cultures of chicken retinal cells, cadherin-6B (cad6B) and cadherin-7 (cad7) are expressed by distinct neurones, each being distributed in a punctate pattern along their neurites as well as in the soma. Double-immunostaining for cad6B and PSD-95/SAP90 or other PSD-95 family members, known to localize in the postsynaptic density, showed that their distributions overlapped each other. To assess the role for cad6B, we incubated retinal cells with antibodies that could specifically block cad6B-mediated adhesion. In the antibody-treated neurones, the localization pattern of PSD-95 family proteins was altered, that is, their staining signals tended to be reduced or disarranged. We then examined whether cadherins interacted molecularly with PSD-95: Cadherin immunoprecipitates from brain lysates did not contain PSD-95; nevertheless, this protein was co-precipitated with alphaN- and beta-catenins. When PSD-95 proteins were ectopically expressed in epithelial cells, some of these molecules were concentrated in cell-cell junctions, co-localizing with E-cadherin, and this junctional localization of PSD-95 was abolished by blocking of E-cadherin activity. CONCLUSION These results suggest that cadherins play a role in the subcellular organization of postsynaptic density components through some, perhaps indirect, molecular interactions.
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Affiliation(s)
- Y Honjo
- Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
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Abstract
A family of proteins has been identified whose members, the Shanks, physically link two major receptor complexes at excitatory synapses - NMDA receptors and metabotropic glutamate receptors.
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Affiliation(s)
- M D Ehlers
- Department of Neurobiology, Duke University Medical Center, Durham, 27710, USA.
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Tu JC, Xiao B, Naisbitt S, Yuan JP, Petralia RS, Brakeman P, Doan A, Aakalu VK, Lanahan AA, Sheng M, Worley PF. Coupling of mGluR/Homer and PSD-95 complexes by the Shank family of postsynaptic density proteins. Neuron 1999; 23:583-92. [PMID: 10433269 DOI: 10.1016/s0896-6273(00)80810-7] [Citation(s) in RCA: 833] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Shank is a recently described family of postsynaptic proteins that function as part of the NMDA receptor-associated PSD-95 complex (Naisbitt et al., 1999 [this issue of Neuron]). Here, we report that Shank proteins also bind to Homer. Homer proteins form multivalent complexes that bind proline-rich motifs in group 1 metabotropic glutamate receptors and inositol trisphosphate receptors, thereby coupling these receptors in a signaling complex. A single Homer-binding site is identified in Shank, and Shank and Homer coimmunoprecipitate from brain and colocalize at postsynaptic densities. Moreover, Shank clusters mGluR5 in heterologous cells in the presence of Homer and mediates the coclustering of Homer with PSD-95/GKAP. Thus, Shank may cross-link Homer and PSD-95 complexes in the PSD and play a role in the signaling mechanisms of both mGluRs and NMDA receptors.
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Affiliation(s)
- J C Tu
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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