251
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The RhoA-associated protein Citron-N controls dendritic spine maintenance by interacting with spine-associated Golgi compartments. EMBO Rep 2008; 9:384-92. [PMID: 18309323 DOI: 10.1038/embor.2008.21] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 01/18/2008] [Accepted: 01/21/2008] [Indexed: 11/08/2022] Open
Abstract
Dendritic spines are highly dynamic protuberances that are thought to be crucial for learning and memory. Although it is well known that actin filaments and membrane dynamics regulate spine plasticity, how these two events are linked locally is less clear. Here, we provide evidence that Citron-N (CIT-N), a binding partner of the small GTPase RhoA, is associated with the actin filaments and Golgi compartments of dendritic spines. We also show that CIT-N is required for recruiting F-actin and Golgi membranes at spines of in vitro-grown neurons. Studies in knockout mice show that this protein is essential for the maturation of dendritic spines. We suggest that CIT-N might function as a scaffold protein in spine organization through its ability to bind to Golgi membranes and by affecting actin remodelling.
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252
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Inhibition of Arp2/3-mediated actin polymerization by PICK1 regulates neuronal morphology and AMPA receptor endocytosis. Nat Cell Biol 2008; 10:259-71. [PMID: 18297063 DOI: 10.1038/ncb1688] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 01/25/2008] [Indexed: 02/07/2023]
Abstract
The dynamic regulation of actin polymerization plays crucial roles in cell morphology and endocytosis. The mechanistic details of these processes and the proteins involved are not fully understood, especially in neurons. PICK1 is a PDZ-BAR-domain protein involved in regulated AMPA receptor (AMPAR) endocytosis in neurons. Here, we demonstrate that PICK1 binds filamentous (F)-actin and the actin-nucleating Arp2/3 complex, and potently inhibits Arp2/3-mediated actin polymerization. RNA interference (RNAi) knockdown of PICK1 in neurons induces a reorganization of the actin cytoskeleton resulting in aberrant cell morphology. Wild-type PICK1 rescues this phenotype, but a mutant PICK1, PICK1(W413A), that does not bind or inhibit Arp2/3 has no effect. Furthermore, this mutant also blocks NMDA-induced AMPAR internalization. This study identifies PICK1 as a negative regulator of Arp2/3-mediated actin polymerization that is critical for a specific form of vesicle trafficking, and also for the development of neuronal architecture.
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253
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Neco P, Fernández-Peruchena C, Navas S, Gutiérrez LM, de Toledo GA, Alés E. Myosin II contributes to fusion pore expansion during exocytosis. J Biol Chem 2008; 283:10949-57. [PMID: 18283106 DOI: 10.1074/jbc.m709058200] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis, the fusion pore expands to allow release of neurotransmitters and hormones to the extracellular space. To understand the process of synaptic transmission, it is of outstanding importance to know the properties of the fusion pore and how these properties affect the release process. Many proteins have been implicated in vesicle fusion; however, there is little evidence for proteins involved in fusion pore expansion. Myosin II has been shown to participate in the transport of vesicles and, surprisingly, in the final phases of exocytosis, affecting the kinetics of catecholamine release in adrenal chromaffin cells as measured by amperometry. Here, we have studied single vesicle exocytosis in chromaffin cells overexpressing an unphosphorylatable form (T18AS19A RLC-GFP) of myosin II that produces an inactive protein by patch amperometry. This method allows direct determination of fusion pore expansion by measuring its conductance, whereas the release of catecholamines is recorded simultaneously by amperometry. Here we demonstrated that the fusion pore is of critical importance to control the release of catecholamines during single vesicle secretion in chromaffin cells. We proved that myosin II acts as a molecular motor on the fusion pore expansion by hindering its dilation when it lacks the phosphorylation sites.
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Affiliation(s)
- Patricia Neco
- Departamento Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla 41009, Spain
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254
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Srinivasan G, Kim JH, von Gersdorff H. The pool of fast releasing vesicles is augmented by myosin light chain kinase inhibition at the calyx of Held synapse. J Neurophysiol 2008; 99:1810-24. [PMID: 18256166 DOI: 10.1152/jn.00949.2007] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Synaptic strength is determined by release probability and the size of the readily releasable pool of docked vesicles. Here we describe the effects of blocking myosin light chain kinase (MLCK), a cytoskeletal regulatory protein thought to be involved in myosin-mediated vesicle transport, on synaptic transmission at the mouse calyx of Held synapse. Application of three different MLCK inhibitors increased the amplitude of the early excitatory postsynaptic currents (EPSCs) in a stimulus train, without affecting the late steady-state EPSCs. A presynaptic locus of action for MLCK inhibitors was confirmed by an increase in the frequency of miniature EPSCs that left their average amplitude unchanged. MLCK inhibition did not affect presynaptic Ca(2+) currents or action potential waveform. Moreover, Ca(2+) imaging experiments showed that [Ca(2+)](i) transients elicited by 100-Hz stimulus trains were not altered by MLCK inhibition. Studies using high-frequency stimulus trains indicated that MLCK inhibitors increase vesicle pool size, but do not significantly alter release probability. Accordingly, when AMPA-receptor desensitization was minimized, EPSC paired-pulse ratios were unaltered by MLCK inhibition, suggesting that release probability remains unaltered. MLCK inhibition potentiated EPSCs even when presynaptic Ca(2+) buffering was greatly enhanced by treating slices with EGTA-AM. In addition, MLCK inhibition did not affect the rate of recovery from short-term depression. Finally, developmental studies revealed that EPSC potentiation by MLCK inhibition starts at postnatal day 5 (P5) and remains strong during synaptic maturation up to P18. Overall, our data suggest that MLCK plays a crucial role in determining the size of the pool of synaptic vesicles that undergo fast release at a CNS synapse.
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Affiliation(s)
- Geetha Srinivasan
- The Vollum Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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255
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Brodbeck J, Balestra ME, Saunders AM, Roses AD, Mahley RW, Huang Y. Rosiglitazone increases dendritic spine density and rescues spine loss caused by apolipoprotein E4 in primary cortical neurons. Proc Natl Acad Sci U S A 2008; 105:1343-6. [PMID: 18212130 PMCID: PMC2234140 DOI: 10.1073/pnas.0709906104] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Indexed: 11/18/2022] Open
Abstract
Convergent evidence has revealed an association between insulin resistance and Alzheimer's disease (AD), and the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, rosiglitazone, an insulin sensitizer and mitochondrial activator, improves cognition in patients with early or mild-to-moderate AD. Apolipoprotein (apo) E4, a major genetic risk factor for AD, exerts neuropathological effects through multiple pathways, including impairment of dendritic spine structure and mitochondrial function. Here we show that rosiglitazone significantly increased dendritic spine density in a dose-dependent manner in cultured primary cortical rat neurons. This effect was abolished by the PPAR-gamma-specific antagonist, GW9662, suggesting that rosiglitazone exerts this effect by activating the PPAR-gamma pathway. Furthermore, the C-terminal-truncated fragment of apoE4 significantly decreased dendritic spine density. Rosiglitazone rescued this detrimental effect. Thus, rosiglitazone might improve cognition in AD patients by increasing dendritic spine density.
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Affiliation(s)
| | | | - Ann M. Saunders
- GlaxoSmithKline Research and Development, Research Triangle Park, NC 27709
| | - Allen D. Roses
- GlaxoSmithKline Research and Development, Research Triangle Park, NC 27709
| | - Robert W. Mahley
- *Gladstone Institute of Neurological Disease and
- Gladstone Institute of Cardiovascular Disease, The J. David Gladstone Institutes, 1650 Owens Street, San Francisco, CA 94158
- Departments of Medicine
- Pathology, and
- Cardiovascular Research Institute, University of California, San Francisco, CA 94143; and
| | - Yadong Huang
- *Gladstone Institute of Neurological Disease and
- Gladstone Institute of Cardiovascular Disease, The J. David Gladstone Institutes, 1650 Owens Street, San Francisco, CA 94158
- Pathology, and
- Neurology and
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256
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Affiliation(s)
- Rachel McMullan
- Medical Research Council Cell Biology Unit, MRC Laboratory for Molecular Cell Biology and Department of Pharmacology, University College, London WC1E 6BT, United Kingdom
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257
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Cohen S, Greenberg ME. Communication between the synapse and the nucleus in neuronal development, plasticity, and disease. Annu Rev Cell Dev Biol 2008; 24:183-209. [PMID: 18616423 PMCID: PMC2709812 DOI: 10.1146/annurev.cellbio.24.110707.175235] [Citation(s) in RCA: 317] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Sensory experience is critical for the proper development and plasticity of the brain throughout life. Successful adaptation to the environment is necessary for the survival of an organism, and this process requires the translation of specific sensory stimuli into changes in the structure and function of relevant neural circuits. Sensory-evoked activity drives synaptic input onto neurons within these behavioral circuits, initiating membrane depolarization and calcium influx into the cytoplasm. Calcium signaling triggers the molecular mechanisms underlying neuronal adaptation, including the activity-dependent transcriptional programs that drive the synthesis of the effector molecules required for long-term changes in neuronal function. Insight into the signaling pathways between the synapse and the nucleus that translate specific stimuli into altered patterns of connectivity within a circuit provides clues as to how activity-dependent programs of gene expression are coordinated and how disruptions in this process may contribute to disorders of cognitive function.
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Affiliation(s)
- Sonia Cohen
- F.M. Kirby Neurobiology Center, Children's Hospital Boston and Departments of Neurology and Neurobiology, Boston, Massachusetts 02115
- Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115
| | - Michael E. Greenberg
- F.M. Kirby Neurobiology Center, Children's Hospital Boston and Departments of Neurology and Neurobiology, Boston, Massachusetts 02115
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258
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Lopatina NG, Zachepilo TG, Savvateeva-Popova EV. LIM kinase-1 in the cerebral ganglion of Drosophila with genetic disturbances of kynurenine balance. DOKLADY BIOLOGICAL SCIENCES : PROCEEDINGS OF THE ACADEMY OF SCIENCES OF THE USSR, BIOLOGICAL SCIENCES SECTIONS 2008; 418:1-3. [PMID: 21249536 DOI: 10.1134/s0012496608010018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Indexed: 05/30/2023]
Affiliation(s)
- N G Lopatina
- Pavlov Institute of Physiology, Russian Academy of Sciences, nab. Makarova 6, St. Petersburg, 199034, Russia
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259
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Mashaly A, Winkler M, Frambach I, Gras H, Schürmann FW. Sprouting interneurons in mushroom bodies of adult cricket brains. J Comp Neurol 2008; 508:153-74. [DOI: 10.1002/cne.21660] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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260
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The role of actin remodeling in the trafficking of intracellular vesicles, transporters, and channels: focusing on aquaporin-2. Pflugers Arch 2007; 456:737-45. [DOI: 10.1007/s00424-007-0404-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Revised: 11/12/2007] [Accepted: 11/15/2007] [Indexed: 01/06/2023]
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261
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Desnos C, Huet S, Fanget I, Chapuis C, Böttiger C, Racine V, Sibarita JB, Henry JP, Darchen F. Myosin va mediates docking of secretory granules at the plasma membrane. J Neurosci 2007; 27:10636-45. [PMID: 17898234 PMCID: PMC6673143 DOI: 10.1523/jneurosci.1228-07.2007] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Myosin Va (MyoVa) is a prime candidate for controlling actin-based organelle motion in neurons and neuroendocrine cells. Its function in secretory granule (SG) trafficking was investigated in enterochromaffin cells by wide-field and total internal reflection fluorescence microscopy. The distribution of endogenous MyoVa partially overlapped with SGs and microtubules. Impairing MyoVa function by means of a truncated construct (MyoVa tail) or RNA interference prevented the formation of SG-rich regions at the cell periphery and reduced SG density in the subplasmalemmal region. Individual SG trajectories were tracked to analyze SG mobility. A wide distribution of their diffusion coefficient, D(xy), was observed. Almost immobile SGs (D(xy) < 5 x 10(-4) microm2 x s(-1)) were considered as docked at the plasma membrane based on two properties: (1) SGs that undergo exocytosis have a D(xy) below this threshold value for at least 2 s before fusion; (2) a negative autocorrelation of the vertical motion was found in subtrajectories with a D(xy) below the threshold. Using this criterion of docking, we found that the main effect of MyoVa inhibition was to reduce the number of docked granules, leading to reduced secretory responses. Surprisingly, this reduction was not attributable to a decreased transport of SGs toward release sites. In contrast, MyoVa silencing reduced the occurrence of long-lasting, but not short-lasting, docking periods. We thus propose that, despite its known motor activity, MyoVa directly mediates stable attachment of SGs at the plasma membrane.
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Affiliation(s)
- Claire Desnos
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - Sébastien Huet
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - Isabelle Fanget
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - Catherine Chapuis
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - Caroline Böttiger
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - Victor Racine
- Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 144, 75248 Paris Cedex 05, France
| | - Jean-Baptiste Sibarita
- Institut Curie, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 144, 75248 Paris Cedex 05, France
| | - Jean-Pierre Henry
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
| | - François Darchen
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Propre de Recherche 1929, Université Paris 7 Denis Diderot, 75005 Paris, France, and
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262
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Abstract
F-actin remodelling has been implicated in regulated secretion from many cell types, in particular secretion from neuron axon terminals and neuroendocrine cell types. Cortical F-actin has long been postulated to act as a barrier to vesicle movement and hence to inhibit secretion; however, more recent studies point to F-actin remodelling providing both supporting and restraining roles in secretion. Magnocellular neurons of the supraoptic nucleus secrete either oxytocin or vasopressin from their dendrites as well as their axon terminals; and peptide release from these two compartments can be differentially controlled to allow secretion from one compartment in isolation from the other. While oxytocin and vasopressin secretion can be provoked by F-actin depolymerization in both compartments, acutely stimulated secretion is dependent on F-actin remodelling in dendrites but not axon terminals, suggesting that F-actin plays a different role in regulating the readily releasable pool of secretory vesicles in the two compartments. In addition, activity-dependent secretion from the dendritic compartment can be primed by prior exposure to agents, including oxytocin, that stimulate release of Ca2+ from intracellular stores. While remodelling of F-actin is involved, it is not solely responsible for priming secretory responses.
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263
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Kwiatkowski AV, Weis WI, Nelson WJ. Catenins: playing both sides of the synapse. Curr Opin Cell Biol 2007; 19:551-6. [PMID: 17936606 DOI: 10.1016/j.ceb.2007.08.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2007] [Accepted: 08/14/2007] [Indexed: 12/11/2022]
Abstract
Synapses of the central nervous system (CNS) are specialized cell-cell junctions that mediate intercellular signal transmission from one neuron to another. The directional nature of signal relay requires synaptic contacts to be morphologically asymmetric with distinct protein components, while changes in synaptic communication during neural network formation require synapses to be plastic. Synapse morphology and plasticity require a dynamic actin cytoskeleton. Classical cadherins, which are junctional proteins associated with the actin cytoskeleton, localize to synapses and regulate synaptic adhesion, stability and remodeling. The major intracellular components of cadherin junctions are the catenin proteins, and increasing evidence suggests that cadherin-catenin complexes modulate an array of synaptic processes. Here we review the role of catenins in regulating the development of pre- and postsynaptic compartments and function in synaptic plasticity, with particular focus on their role in regulating the actin cytoskeleton.
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Affiliation(s)
- Adam V Kwiatkowski
- Department of Biological Sciences, Stanford University, Stanford, CA 94305, United States.
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264
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Lee CW, Peng HB. The function of mitochondria in presynaptic development at the neuromuscular junction. Mol Biol Cell 2007; 19:150-8. [PMID: 17942598 DOI: 10.1091/mbc.e07-05-0515] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Mitochondria with high membrane potential (DeltaPsi(m)) are enriched in the presynaptic nerve terminal at vertebrate neuromuscular junctions, but the exact function of these localized synaptic mitochondria remains unclear. Here, we investigated the correlation between mitochondrial DeltaPsi(m) and the development of synaptic specializations. Using mitochondrial DeltaPsi(m)-sensitive probe JC-1, we found that DeltaPsi(m) in Xenopus spinal neurons could be reversibly elevated by creatine and suppressed by FCCP. Along naïve neurites, preexisting synaptic vesicle (SV) clusters were positively correlated with mitochondrial DeltaPsi(m), suggesting a potential regulatory role of mitochondrial activity in synaptogenesis. Indicating a specific role of mitochondrial activity in presynaptic development, mitochondrial ATP synthase inhibitor oligomycin, but not mitochondrial Na(+)/Ca(2+) exchanger inhibitor CGP-37157, inhibited the clustering of SVs induced by growth factor-coated beads. Local F-actin assembly induced along spinal neurites by beads was suppressed by FCCP or oligomycin. Our results suggest that a key role of presynaptic mitochondria is to provide ATP for the assembly of actin cytoskeleton involved in the assembly of the presynaptic specialization including the clustering of SVs and mitochondria themselves.
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Affiliation(s)
- Chi Wai Lee
- Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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265
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Lopatina NG, Zachepilo TG, Chesnokova EG, Savvateeva-Popova EV. Mutations in structural genes of tryptophan metabolic enzymes of the kynurenine pathway modulate some units of the L-glutamate receptor-actin cytoskeleton signaling cascade. RUSS J GENET+ 2007. [DOI: 10.1134/s1022795407100110] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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266
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Jelen N, Ule J, Živin M, Darnell RB. Evolution of Nova-dependent splicing regulation in the brain. PLoS Genet 2007; 3:1838-47. [PMID: 17937501 PMCID: PMC2014790 DOI: 10.1371/journal.pgen.0030173] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Accepted: 08/24/2007] [Indexed: 01/08/2023] Open
Abstract
A large number of alternative exons are spliced with tissue-specific patterns, but little is known about how such patterns have evolved. Here, we study the conservation of the neuron-specific splicing factors Nova1 and Nova2 and of the alternatively spliced exons they regulate in mouse brain. Whereas Nova RNA binding domains are 94% identical across vertebrate species, Nova-dependent splicing silencer and enhancer elements (YCAY clusters) show much greater divergence, as less than 50% of mouse YCAY clusters are conserved at orthologous positions in the zebrafish genome. To study the relation between the evolution of tissue-specific splicing and YCAY clusters, we compared the brain-specific splicing of Nova-regulated exons in zebrafish, chicken, and mouse. The presence of YCAY clusters in lower vertebrates invariably predicted conservation of brain-specific splicing across species, whereas their absence in lower vertebrates correlated with a loss of alternative splicing. We hypothesize that evolution of Nova-regulated splicing in higher vertebrates proceeds mainly through changes in cis-acting elements, that tissue-specific splicing might in some cases evolve in a single step corresponding to evolution of a YCAY cluster, and that the conservation level of YCAY clusters relates to the functions encoded by the regulated RNAs.
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Affiliation(s)
- Nejc Jelen
- Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, New York, United States of America
- Howard Hughes Medical Institute, The Rockefeller University, New York, New York, United States of America
- Division of Structural Studies, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
- Brain Research Laboratory, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | - Jernej Ule
- Division of Structural Studies, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Marko Živin
- Brain Research Laboratory, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | - Robert B Darnell
- Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, New York, United States of America
- Howard Hughes Medical Institute, The Rockefeller University, New York, New York, United States of America
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267
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Abstract
Since the isolation of cyclin-dependent kinase 5 (Cdk5), this proline-directed serine/threonine kinase has been demonstrated as an important regulator of neuronal migration, neuronal survival and synaptic functions. Recently, a number of players implicated in dendrite and synapse development have been identified as Cdk5 substrates. Neurite extension, synapse and spine maturation are all modulated by a myriad of extracellular guidance cues or trophic factors. Cdk5 was recently demonstrated to regulate signaling downstream of some of these extracellular factors, in addition to modulating Rho GTPase activity, which regulates cytoskeletal dynamics. In this communication, we summarize our existing knowledge on the pathways and mechanisms through which Cdk5 affects dendrite, synapse and spine development.
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Affiliation(s)
- Zelda H Cheung
- Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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268
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Faul C, Asanuma K, Yanagida-Asanuma E, Kim K, Mundel P. Actin up: regulation of podocyte structure and function by components of the actin cytoskeleton. Trends Cell Biol 2007; 17:428-37. [PMID: 17804239 DOI: 10.1016/j.tcb.2007.06.006] [Citation(s) in RCA: 412] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 06/15/2007] [Accepted: 06/15/2007] [Indexed: 12/18/2022]
Abstract
Podocytes of the renal glomerulus are unique cells with a complex cellular organization consisting of a cell body, major processes and foot processes. Podocyte foot processes form a characteristic interdigitating pattern with foot processes of neighboring podocytes, leaving in between the filtration slits that are bridged by the glomerular slit diaphragm. The highly dynamic foot processes contain an actin-based contractile apparatus comparable to that of smooth muscle cells or pericytes. Mutations affecting several podocyte proteins lead to rearrangement of the actin cytoskeleton, disruption of the filtration barrier and subsequent renal disease. The fact that the dynamic regulation of the podocyte cytoskeleton is vital to kidney function has led to podocytes emerging as an excellent model system for studying actin cytoskeleton dynamics in a physiological context.
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Affiliation(s)
- Christian Faul
- Department of Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA
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269
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Desnos C, Huet S, Darchen F. 'Should I stay or should I go?': myosin V function in organelle trafficking. Biol Cell 2007; 99:411-23. [PMID: 17635110 DOI: 10.1042/bc20070021] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Actin- and microtubule-based motors can propel different cargos along filaments. Within cells, they control the distribution of membrane-bound compartments by performing complementary tasks. Organelles make long journeys along microtubules, with class V myosins ensuring their capture and their dispersal in actin-rich regions. Myosin Va is recruited on to diverse organelles, such as melanosomes and secretory vesicles, by a mechanism involving Rab GTPases. The role of myosin Va in the recruitment of secretory vesicles at the plasma membrane reveals that the cortical actin network cannot merely be seen as a physical barrier hindering vesicle access to release sites. In neurons, myosin Va controls the targeting of IP(3) (inositol 1,4,5-trisphosphate)-sensitive Ca(2+) stores to dendritic spines and the transport of mRNAs. These defects probably account for the severe neurological symptoms observed in Griscelli syndrome due to mutations in the MYO5A gene.
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Affiliation(s)
- Claire Desnos
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, UPR 1929, Université Paris 7 Denis Diderot, Paris, France.
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270
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Okuda T, Yu LMY, Cingolani LA, Kemler R, Goda Y. beta-Catenin regulates excitatory postsynaptic strength at hippocampal synapses. Proc Natl Acad Sci U S A 2007; 104:13479-84. [PMID: 17679699 PMCID: PMC1948936 DOI: 10.1073/pnas.0702334104] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The precise contribution of the cadherin-beta-catenin synapse adhesion complex in the functional and structural changes associated with the pre- and postsynaptic terminals remains unclear. Here we report a requirement for endogenous beta-catenin in regulating synaptic strength and dendritic spine morphology in cultured hippocampal pyramidal neurons. Ablating beta-catenin after the initiation of synaptogenesis in the postsynaptic neuron reduces the amplitude of spontaneous excitatory synaptic responses without a concurrent change in their frequency and synapse density. The normal glutamatergic synaptic response is maintained by postsynaptic beta-catenin in a cadherin-dependent manner and requires the C-terminal PDZ-binding motif of beta-catenin but not the link to the actin cytoskeleton. In addition, ablating beta-catenin in postsynaptic neurons accompanies a block of bidirectional quantal scaling of glutamatergic responses induced by chronic activity manipulation. In older cultures at a time when neurons have abundant dendritic spines, neurons ablated for beta-catenin show thin, elongated spines and reduced proportion of mushroom spines without a change in spine density. Collectively, these findings suggest that the cadherin-beta-catenin complex is an integral component of synaptic strength regulation and plays a basic role in coupling synapse function and spine morphology.
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Affiliation(s)
- Takashi Okuda
- *Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit
| | - Lily M. Y. Yu
- *Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom; and
| | - Lorenzo A. Cingolani
- *Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit
| | - Rolf Kemler
- Department of Molecular Embryology, Max Planck Institute of Immunobiology, Stuebeweg 51, D-79108 Freiburg, Germany
| | - Yukiko Goda
- *Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom; and
- To whom correspondence should be addressed at:
Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom. E-mail:
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271
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Besse F, Mertel S, Kittel RJ, Wichmann C, Rasse TM, Sigrist SJ, Ephrussi A. The Ig cell adhesion molecule Basigin controls compartmentalization and vesicle release at Drosophila melanogaster synapses. ACTA ACUST UNITED AC 2007; 177:843-55. [PMID: 17548512 PMCID: PMC2064284 DOI: 10.1083/jcb.200701111] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Synapses can undergo rapid changes in size as well as in their vesicle release function during both plasticity processes and development. This fundamental property of neuronal cells requires the coordinated rearrangement of synaptic membranes and their associated cytoskeleton, yet remarkably little is known of how this coupling is achieved. In a GFP exon-trap screen, we identified Drosophila melanogaster Basigin (Bsg) as an immunoglobulin domain-containing transmembrane protein accumulating at periactive zones of neuromuscular junctions. Bsg is required pre- and postsynaptically to restrict synaptic bouton size, its juxtamembrane cytoplasmic residues being important for that function. Bsg controls different aspects of synaptic structure, including distribution of synaptic vesicles and organization of the presynaptic cortical actin cytoskeleton. Strikingly, bsg function is also required specifically within the presynaptic terminal to inhibit nonsynchronized evoked vesicle release. We thus propose that Bsg is part of a transsynaptic complex regulating synaptic compartmentalization and strength, and coordinating plasma membrane and cortical organization.
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Affiliation(s)
- Florence Besse
- Developmental Biology Unit, European Molecular Biology Laboratory, D-69117 Heidelberg, Germany
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272
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273
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Berto G, Camera P, Fusco C, Imarisio S, Ambrogio C, Chiarle R, Silengo L, Di Cunto F. The Down syndrome critical region protein TTC3 inhibits neuronal differentiation via RhoA and Citron kinase. J Cell Sci 2007; 120:1859-67. [PMID: 17488780 DOI: 10.1242/jcs.000703] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The Down syndrome critical region (DSCR) on Chromosome 21 contains many genes whose duplication may lead to the major phenotypic features of Down syndrome and especially the associated mental retardation. However, the functions of DSCR genes are mostly unknown and their possible involvement in key brain developmental events still largely unexplored. In this report we show that the protein TTC3, encoded by one of the main DSCR candidate genes, physically interacts with Citron kinase (CIT-K) and Citron N (CIT-N), two effectors of the RhoA small GTPase that have previously been involved in neuronal proliferation and differentiation. More importantly, we found that TTC3 levels can strongly affect the NGF-induced differentiation of PC12 cells, by a CIT-K-dependent mechanism. Indeed, TTC3 overexpression leads to strong inhibition of neurite extension, which can be reverted by CIT-K RNAi. Conversely, TTC3 knockdown stimulates neurite extension in the same cells. Finally, we find that Rho, but not Rho kinase, is required for TTC3 differentiation-inhibiting activity. Our results suggest that the TTC3-RhoA-CIT-K pathway could be a crucial determinant of in vivo neuronal development, whose hyperactivity may result in detrimental effects on the normal differentiation program.
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Affiliation(s)
- Gaia Berto
- Molecular Biotechnology Center, Department of Genetics, Biology and Biochemistry, University of Turin, Italy
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274
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Pilo Boyl P, Di Nardo A, Mulle C, Sassoè-Pognetto M, Panzanelli P, Mele A, Kneussel M, Costantini V, Perlas E, Massimi M, Vara H, Giustetto M, Witke W. Profilin2 contributes to synaptic vesicle exocytosis, neuronal excitability, and novelty-seeking behavior. EMBO J 2007; 26:2991-3002. [PMID: 17541406 PMCID: PMC1894775 DOI: 10.1038/sj.emboj.7601737] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Accepted: 05/03/2007] [Indexed: 11/08/2022] Open
Abstract
Profilins are actin binding proteins essential for regulating cytoskeletal dynamics, however, their function in the mammalian nervous system is unknown. Here, we provide evidence that in mouse brain profilin1 and profilin2 have distinct roles in regulating synaptic actin polymerization with profilin2 preferring a WAVE-complex-mediated pathway. Mice lacking profilin2 show a block in synaptic actin polymerization in response to depolarization, which is accompanied by increased synaptic excitability of glutamatergic neurons due to higher vesicle exocytosis. These alterations in neurotransmitter release correlate with a hyperactivation of the striatum and enhanced novelty-seeking behavior in profilin2 mutant mice. Our results highlight a novel, profilin2-dependent pathway, regulating synaptic physiology, neuronal excitability, and complex behavior.
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Affiliation(s)
| | | | - Christophe Mulle
- UMR CNRS 5091, Institut François Magendie, Physiologie Cellulaire de la Synapse, Bordeaux, France
| | - Marco Sassoè-Pognetto
- Department of Anatomy, Pharmacology and Forensic Medicine and Istituto Nazionale di Neuroscienze, University of Turin, Torino, Italy
| | - Patrizia Panzanelli
- Department of Anatomy, Pharmacology and Forensic Medicine and Istituto Nazionale di Neuroscienze, University of Turin, Torino, Italy
| | - Andrea Mele
- Università di Roma ‘La Sapienza', Laboratorio di Psicobiologia, Dipart. di Genetica e Biologia Molecolare, Roma, Italy
| | - Matthias Kneussel
- Centre for Molecular Neurobiology, ZMNH, University of Hamburg, Hamburg, Germany
| | - Vivian Costantini
- Università di Roma ‘La Sapienza', Laboratorio di Psicobiologia, Dipart. di Genetica e Biologia Molecolare, Roma, Italy
| | | | | | - Hugo Vara
- Department of Anatomy, Pharmacology and Forensic Medicine and Istituto Nazionale di Neuroscienze, University of Turin, Torino, Italy
| | - Maurizio Giustetto
- Department of Anatomy, Pharmacology and Forensic Medicine and Istituto Nazionale di Neuroscienze, University of Turin, Torino, Italy
| | - Walter Witke
- EMBL, Mouse Biology Unit, Monterotondo, Italy
- EMBL, Mouse Biology Unit, Adriano Buzzati-Traverso Campus, Via Ramarini 32, 00015 Monterotondo, Italy. Tel.: +0039 06 90091 268; Fax: +0039 06 90091 272; E-mail:
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275
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O’Malley D, MacDonald N, Mizielinska S, Connolly CN, Irving AJ, Harvey J. Leptin promotes rapid dynamic changes in hippocampal dendritic morphology. Mol Cell Neurosci 2007; 35:559-72. [PMID: 17618127 PMCID: PMC1995039 DOI: 10.1016/j.mcn.2007.05.001] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Revised: 04/24/2007] [Accepted: 05/01/2007] [Indexed: 01/23/2023] Open
Abstract
Recent studies have implicated the hormone leptin in synaptic plasticity associated with neuronal development and learning and memory. Indeed, leptin facilitates hippocampal long-term potentiation and leptin-insensitive rodents display impaired hippocampal synaptic plasticity suggesting a role for endogenous leptin. Structural changes are also thought to underlie activity-dependent synaptic plasticity and this may be regulated by specific growth factors. As leptin is reported to have neurotrophic actions, we have examined the effects of leptin on the morphology and filopodial outgrowth in hippocampal neurons. Here, we demonstrate that leptin rapidly enhances the motility and density of dendritic filopodia and subsequently increases the density of hippocampal synapses. This process is dependent on the synaptic activation of NR2A-containing NMDA receptors and is mediated by the MAPK (ERK) signaling pathway. As dendritic morphogenesis is associated with activity-dependent changes in synaptic strength, the rapid structural remodeling of dendrites by leptin has important implications for its role in regulating hippocampal synaptic plasticity and neuronal development.
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276
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Tobin VA, Ludwig M. The role of the actin cytoskeleton in oxytocin and vasopressin release from rat supraoptic nucleus neurons. J Physiol 2007; 582:1337-48. [PMID: 17478532 PMCID: PMC2075266 DOI: 10.1113/jphysiol.2007.132639] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Magnocellular neurons of the supraoptic nucleus (SON) can differentially control peptide release from the somato/dendritic and axon terminal compartment. Dendritic release can be selectively regulated through activation of intracellular calcium stores by calcium mobilizers such as thapsigargin (TG), resulting in preparation (priming) of somato/dendritic peptide pools for subsequent activity-dependent release. As dynamic modulation of the actin cytoskeleton is implicated in secretion from synaptic terminals and from several types of neuroendocrine cells, we studied its involvement in oxytocin and vasopressin release from SON neurons. Confocal image analysis of the somata revealed that the normally continuous cortical band of F-actin is disrupted after high potassium (K(+), 50 mm) or TG (200 nm) stimulation. The functional importance of actin remodelling was studied using cell-permeable actin polymerizing (jasplakinolide, 2 microm) or depolymerizing agents (latrunculin B, 5 microm) to treat SON and neural lobe (NL) explants in vitro and measure high K(+)-induced oxytocin and vasopressin release. Latrunculin significantly enhanced, and jasplakinolide inhibited, high-K(+)-evoked somato/dendritic peptide release, while release from axon terminals was not altered, suggesting that high-K(+)-evoked release in the SON, but not the NL, requires depolymerization of the actin cytoskeleton. TG-induced priming of somato/dendritic release was also blocked by jasplakinolide and latrunculin, suggesting that priming involves changes in actin remodelling.
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Affiliation(s)
- Vicky A Tobin
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
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277
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Pinyol R, Haeckel A, Ritter A, Qualmann B, Kessels MM. Regulation of N-WASP and the Arp2/3 complex by Abp1 controls neuronal morphology. PLoS One 2007; 2:e400. [PMID: 17476322 PMCID: PMC1852583 DOI: 10.1371/journal.pone.0000400] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Accepted: 04/04/2007] [Indexed: 11/19/2022] Open
Abstract
Polymerization and organization of actin filaments into complex superstructures is indispensable for structure and function of neuronal networks. We here report that knock down of the F-actin-binding protein Abp1, which is important for endocytosis and synaptic organization, results in changes in axon development virtually identical to Arp2/3 complex inhibition, i.e., a selective increase of axon length. Our in vitro and in vivo experiments demonstrate that Abp1 interacts directly with N-WASP, an activator of the Arp2/3 complex, and releases the autoinhibition of N-WASP in cooperation with Cdc42 and thereby promotes N-WASP-triggered Arp2/3 complex-mediated actin polymerization. In line with our mechanistical studies and the colocalization of Abp1, N-WASP and Arp2/3 at sites of actin polymerization in neurons, we reveal an essential role of Abp1 and its cooperativity with Cdc42 in N-WASP-induced rearrangements of the neuronal cytoskeleton. We furthermore show that introduction of N-WASP mutants lacking the ability to bind Abp1 or Cdc42, Arp2/3 complex inhibition, Abp1 knock down, N-WASP knock down and Arp3 knock down, all cause identical neuromorphological phenotypes. Our data thus strongly suggest that these proteins and their complex formation are important for cytoskeletal processes underlying neuronal network formation.
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Affiliation(s)
- Roser Pinyol
- Research Group Membrane Trafficking and Cytoskeleton, Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
- Research Group Cell Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Akvile Haeckel
- Research Group Membrane Trafficking and Cytoskeleton, Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
- Research Group Cell Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Anett Ritter
- Research Group Membrane Trafficking and Cytoskeleton, Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Britta Qualmann
- Research Group Cell Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Michael Manfred Kessels
- Research Group Membrane Trafficking and Cytoskeleton, Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
- * To whom correspondence should be addressed. E-mail:
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278
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Beuchle D, Schwarz H, Langegger M, Koch I, Aberle H. Drosophila MICAL regulates myofilament organization and synaptic structure. Mech Dev 2007; 124:390-406. [PMID: 17350233 DOI: 10.1016/j.mod.2007.01.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Revised: 01/19/2007] [Accepted: 01/31/2007] [Indexed: 10/23/2022]
Abstract
The overall size and structure of a synaptic terminal is an important determinant of its function. In a large-scale mutagenesis screen, designed to identify Drosophila mutants with abnormally structured neuromuscular junctions (NMJs), we discovered mutations in Drosophila mical, a conserved gene encoding a multi-domain protein with a N-terminal monooxygenase domain. In mical mutants, synaptic boutons do not sprout normally over the muscle surface and tend to form clusters along synaptic branches and at nerve entry sites. Consistent with high expression of MICAL in somatic muscles, immunohistochemical stainings reveal that the subcellular localization and architecture of contractile muscle filaments are dramatically disturbed in mical mutants. Instead of being integrated into a regular sarcomeric pattern, actin and myosin filaments are disorganized and accumulate beneath the plasmamembrane. Whereas contractile elements are strongly deranged, the proposed organizer of sarcomeric structure, D-Titin, is much less affected. Transgenic expression of interfering RNA molecules demonstrates that MICAL is required in muscles for the higher order arrangement of myofilaments. Ultrastructural analysis confirms that myosin-rich thick filaments enter submembranous regions and interfere with synaptic development, indicating that the disorganized myofilaments may cause the synaptic growth phenotype. As a model, we suggest that the filamentous network around synaptic boutons restrains the spreading of synaptic branches.
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Affiliation(s)
- Dirk Beuchle
- Max-Planck-Institute for Developmental Biology, Department III/Genetics, Spemannstr. 35, 72076 Tübingen, Germany
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279
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Deller T, Bas Orth C, Del Turco D, Vlachos A, Burbach GJ, Drakew A, Chabanis S, Korte M, Schwegler H, Haas CA, Frotscher M. A role for synaptopodin and the spine apparatus in hippocampal synaptic plasticity. Ann Anat 2007; 189:5-16. [PMID: 17319604 DOI: 10.1016/j.aanat.2006.06.013] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Spines are considered sites of synaptic plasticity in the brain and are capable of remodeling their shape and size. A molecule thathas been implicated in spine plasticity is the actin-associated protein synaptopodin. This article will review a series of studies aimed at elucidating the role of synaptopodin in the rodent brain. First, the developmental expression of synaptopodin mRNA and protein were studied; secondly, the subcellular localization of synaptopodin in hippocampal principal neurons was analyzed using confocal microscopy as well as electron microscopy and immunogold labelling; and, finally, the functional role of synaptopodin was investigated using a synaptopodin-deficient mouse. The results of these studies are: (1) synaptopodin expression byhippocampal principal neurons develops during the first postnatal weeks and increases in parallel with the maturation of spines in the hippocampus. (2) Synaptopodin is sorted to the spine compartment, where it is tightly associated with the spine apparatus, an enigmatic organelle believed to be involved in calcium storage or local protein synthesis. (3) Synaptopodin-deficient mice generated by gene targeting are viable but lack the spine apparatus organelle. These mice show deficitsin synaptic plasticity as well as impaired learning and memory. Taken together, these data implicate synaptopodin and the spine apparatus in the regulation of synaptic plasticity in the hippocampus. Future studies will be aimed at finding the molecular link between synaptopodin, the spine apparatus organelle, and synaptic plasticity.
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Affiliation(s)
- Thomas Deller
- Institute of Clinical Neuroanatomy, J.W. Goethe-University, Theodor-Stern-Kai 7, D-60590 Frankfurt/Main, Germany.
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280
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Oreiro-García MT, Vázquez-Illanes MD, Sierra-Paredes G, Sierra-Marcuño G. Changes in extracellular amino acid concentrations in the rat hippocampus after in vivo actin depolymerization with latrunculin A. Neurochem Int 2007; 50:734-40. [PMID: 17316902 DOI: 10.1016/j.neuint.2007.01.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Revised: 01/09/2007] [Accepted: 01/11/2007] [Indexed: 10/23/2022]
Abstract
The effect of latrunculin A microperfusion on hippocampal extracellular concentrations of glutamate, aspartate, glycine and GABA, as measured by in vivo microdialysis, was investigated. Latrunculin A (4 microg/ml) was perfused for three consecutive days (8h a day) to promote in vivo F-actin depolymerization. Intrahippocampal latrunculin A microdialysis induced seizures during the second and third day of perfusion, and the animals started showing spontaneous seizures 1 month after lartrunculin A administration. Hippocampal glutamate levels were significantly increased during the first day of latrunculin A microperfusion without significant changes during the second and third day of perfusion. Aspartate levels were significantly increased during the first and second days of treatment. The rise on glutamate and asparate levels was partially reversed by perfusion of NMDA antagonist MK-801. Glycine concentrations were significantly increased during the 3 days of latrunculin A microdialyis, but no significant effect was observed on baseline GABA levels. One month after latrunculin A microperfusion, no significant differences in glutamate and aspartate extracellular concentrations were detected as compared to controls, however, significant increases in glycine and GABA extracellular concentrations were observed. The immediate increases in glutamate, aspartate and glycine levels indicate a modulatory effect of the F-actin cytoskeleton on extracellular concentrations of glutamate, aspartate and glycine. The chronic elevations in GABA and glycine levels are more likely to be related with long-term epileptogenesis processes. Our results suggest that the in vivo biochemical study of actin-dependent processes seems to be a promising approach to the neuropathology and neuropharmacology of epileptic seizures.
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Affiliation(s)
- M Teresa Oreiro-García
- Neuroscience Division, Department of Biochemistry and Molecular Biology, School of Medicine, University of Santiago, San Francisco 1, 15782 Santiago de Compostela, Spain
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281
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Abstract
Synaptic vesicles are key organelles in neurotransmission. Vesicle integral or membrane-associated proteins mediate the various functions the organelle fulfills during its life cycle. These include organelle transport, interaction with the nerve terminal cytoskeleton, uptake and storage of low molecular weight constituents, and the regulated interaction with the pre-synaptic plasma membrane during exo- and endocytosis. Within the past two decades, converging work from several laboratories resulted in the molecular and functional characterization of the proteinaceous inventory of the synaptic vesicle compartment. However, up until recently and due to technical difficulties, it was impossible to screen the entire organelle thoroughly. Recent advances in membrane protein identification and mass spectrometry (MS) have dramatically promoted this field. A comparison of different techniques for elucidating the proteinaceous composition of synaptic vesicles revealed numerous overlaps but also remarkable differences in the protein constituents of the synaptic vesicle compartment, indicating that several protein separation techniques in combination with differing MS approaches are required to identify and characterize the synaptic vesicle proteome. This review highlights the power of various gel separation techniques and MS analyses for the characterization of the proteome of highly purified synaptic vesicles. Furthermore, the newly detected protein assignments to synaptic vesicles, especially those proteins which are new to the inventory of the synaptic vesicle proteome, are critically discussed.
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Affiliation(s)
- Jacqueline Burré
- Institute of Cell Biology and Neuroscience, Neurochemistry, JW Goethe University, Frankfurt, Germany.
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282
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Sekerková G, Diño MR, Ilijic E, Russo M, Zheng L, Bartles JR, Mugnaini E. Postsynaptic enrichment of Eps8 at dendritic shaft synapses of unipolar brush cells in rat cerebellum. Neuroscience 2007; 145:116-29. [PMID: 17223277 PMCID: PMC1892609 DOI: 10.1016/j.neuroscience.2006.11.061] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2006] [Revised: 11/17/2006] [Accepted: 11/20/2006] [Indexed: 01/07/2023]
Abstract
Epidermal growth factor receptor pathway substrate 8 (Eps8) is a widely expressed multidomain signaling protein that coordinates two disparate GTPase-dependent mechanisms: actin reorganization via Ras/Rac pathways and receptor trafficking via Rab5. Expression of Eps8, the gene encoding the founding member of the Eps8 family of proteins, was found in cerebellum by virtual Northern analysis and in situ hybridization. Because the cerebellum has a well-known cellular architecture and is a favored model to study synaptic plasticity and actin dynamics, we sought to analyze Eps8 localization in rat cerebellar neurons and synapses by light and electron microscopy. Specificity of Eps8-antibody was demonstrated by immunoblots and in brain sections. In cerebellum, unipolar brush cells (UBCs) were densely Eps8 immunopositive and granule cells were moderately immunostained. In both types of neuron immunoreaction product was localized to the somatodendritic and axonal compartments. Postsynaptic immunostained foci were demonstrated in the glomeruli in correspondence of the synapses formed by mossy fiber terminals with granule cell and UBC dendrites. These foci appeared especially evident in the UBC brush, which contains an extraordinary postsynaptic apparatus of actin microfilaments facing synaptic junctions of the long and segmented varieties. Eps8 immunoreactivity was conspicuously absent in Purkinje cells and their actin-rich dendritic spines, in all types of inhibitory interneurons of the cerebellum, cerebellar nuclei neurons, and astrocytes. In conclusion, Eps8 protein in cerebellum is expressed exclusively by excitatory cortical interneurons and is intracellularly compartmentalized in a cell-class specific manner. This is the first demonstration of the presence of a member of the Eps8 protein family in UBCs and its enrichment at postsynaptic sites.
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Affiliation(s)
- G Sekerková
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, 320 East Superior Street, Chicago, IL 60611, USA.
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283
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Abstract
Neuronal motility is a fundamental feature that underlies the development, regeneration, and plasticity of the nervous system. Two major developmental events--directed migration of neuronal precursor cells to the proper positions and guided elongation of axons to their target cells--depend on large-scale neuronal motility. At a finer scale, motility is also manifested in many aspects of neuronal structures and functions, ranging from differentiation and refinement of axonal and dendritic morphology during development to synapse remodeling associated with learning and memory in the adult brain. As a primary second messenger that conveys the cytoplasmic actions of electrical activity and many neuroactive ligands, Ca(2+) plays a central role in the regulation of neuronal motility. Recent studies have revealed common Ca(2+)-dependent signaling pathways that are deployed for regulating cytoskeletal dynamics associated with neuronal migration, axon and dendrite development and regeneration, and synaptic plasticity.
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Affiliation(s)
- James Q Zheng
- Department of Neuroscience and Cell Biology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
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284
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Offenhäuser N, Castelletti D, Mapelli L, Soppo BE, Regondi MC, Rossi P, D'Angelo E, Frassoni C, Amadeo A, Tocchetti A, Pozzi B, Disanza A, Guarnieri D, Betsholtz C, Scita G, Heberlein U, Di Fiore PP. Increased ethanol resistance and consumption in Eps8 knockout mice correlates with altered actin dynamics. Cell 2006; 127:213-26. [PMID: 17018287 DOI: 10.1016/j.cell.2006.09.011] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 07/30/2006] [Accepted: 09/08/2006] [Indexed: 01/18/2023]
Abstract
Dynamic modulation of the actin cytoskeleton is critical for synaptic plasticity, abnormalities of which are thought to contribute to mental illness and addiction. Here we report that mice lacking Eps8, a regulator of actin dynamics, are resistant to some acute intoxicating effects of ethanol and show increased ethanol consumption. In the brain, the N-methyl-D-aspartate (NMDA) receptor is a major target of ethanol. We show that Eps8 is localized to postsynaptic structures and is part of the NMDA receptor complex. Moreover, in Eps8 null mice, NMDA receptor currents and their sensitivity to inhibition by ethanol are abnormal. In addition, Eps8 null neurons are resistant to the actin-remodeling activities of NMDA and ethanol. We propose that proper regulation of the actin cytoskeleton is a key determinant of cellular and behavioral responses to ethanol.
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Affiliation(s)
- Nina Offenhäuser
- Fondazione Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139 Milan, Italy.
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285
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Tang VW. Proteomic and bioinformatic analysis of epithelial tight junction reveals an unexpected cluster of synaptic molecules. Biol Direct 2006; 1:37. [PMID: 17156438 PMCID: PMC1712231 DOI: 10.1186/1745-6150-1-37] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Accepted: 12/08/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Zonula occludens, also known as the tight junction, is a specialized cell-cell interaction characterized by membrane "kisses" between epithelial cells. A cytoplasmic plaque of approximately 100 nm corresponding to a meshwork of densely packed proteins underlies the tight junction membrane domain. Due to its enormous size and difficulties in obtaining a biochemically pure fraction, the molecular composition of the tight junction remains largely unknown. RESULTS A novel biochemical purification protocol has been developed to isolate tight junction protein complexes from cultured human epithelial cells. After identification of proteins by mass spectroscopy and fingerprint analysis, candidate proteins are scored and assessed individually. A simple algorithm has been devised to incorporate transmembrane domains and protein modification sites for scoring membrane proteins. Using this new scoring system, a total of 912 proteins have been identified. These 912 hits are analyzed using a bioinformatics approach to bin the hits in 4 categories: configuration, molecular function, cellular function, and specialized process. Prominent clusters of proteins related to the cytoskeleton, cell adhesion, and vesicular traffic have been identified. Weaker clusters of proteins associated with cell growth, cell migration, translation, and transcription are also found. However, the strongest clusters belong to synaptic proteins and signaling molecules. Localization studies of key components of synaptic transmission have confirmed the presence of both presynaptic and postsynaptic proteins at the tight junction domain. To correlate proteomics data with structure, the tight junction has been examined using electron microscopy. This has revealed many novel structures including end-on cytoskeletal attachments, vesicles fusing/budding at the tight junction membrane domain, secreted substances encased between the tight junction kisses, endocytosis of tight junction double membranes, satellite Golgi apparatus and associated vesicular structures. A working model of the tight junction consisting of multiple functions and sub-domains has been generated using the proteomics and structural data. CONCLUSION This study provides an unbiased proteomics and bioinformatics approach to elucidate novel functions of the tight junction. The approach has revealed an unexpected cluster associating with synaptic function. This surprising finding suggests that the tight junction may be a novel epithelial synapse for cell-cell communication. REVIEWERS This article was reviewed by Gáspár Jékely, Etienne Joly and Neil Smalheiser.
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Affiliation(s)
- Vivian W Tang
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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286
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Andrieux A, Salin P, Schweitzer A, Bégou M, Pachoud B, Brun P, Gory-Fauré S, Kujala P, Suaud-Chagny MF, Höfle G, Job D. Microtubule stabilizer ameliorates synaptic function and behavior in a mouse model for schizophrenia. Biol Psychiatry 2006; 60:1224-30. [PMID: 16806091 DOI: 10.1016/j.biopsych.2006.03.048] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2005] [Revised: 03/13/2006] [Accepted: 03/14/2006] [Indexed: 10/24/2022]
Abstract
BACKGROUND Recent data suggest that cytoskeletal defects may play a role in schizophrenia. We previously imitated features of schizophrenia in an animal model by disrupting gene coding for a microtubule-associated protein called STOP. STOP-null mice display synaptic defects in glutamatergic neurons, hyper-dopaminergy, and severe behavioral disorders. Synaptic and behavioral deficits are amended by neuroleptic treatment in STOP-null mice, providing an attractive model to test new antipsychotic agents. We examined the effects of a taxol-related microtubule stabilizer, epothilone D. METHODS Mice were treated either with vehicle alone or with epothilone D. Treatment effects on synaptic function were assessed using electron-microscopy quantification of synaptic vesicle pools and electrophysiology in the CA1 region of the hippocampus. Dopamine transmission was investigated using electrochemical assays. Behavior was principally assessed using tests of maternal skills. RESULTS In STOP-null mice, treatment with epothilone D increased synaptic vesicle pools, ameliorated both short- and long-term forms of synaptic plasticity in glutamatergic neurons, and had a dramatic beneficial effect on mouse behavior. CONCLUSIONS A microtubule stabilizer can have a beneficial effect on synaptic function and behavior, suggesting new possibilities for treatment of schizophrenia.
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Affiliation(s)
- Annie Andrieux
- Laboratoire du Cytosquelette, INSERM U366 CEA, Département Réponse et Dynamique Cellulaire, Grenoble, France.
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287
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Lorusso A, Covino C, Priori G, Bachi A, Meldolesi J, Chieregatti E. Annexin2 coating the surface of enlargeosomes is needed for their regulated exocytosis. EMBO J 2006; 25:5443-56. [PMID: 17082761 PMCID: PMC1679766 DOI: 10.1038/sj.emboj.7601419] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Accepted: 10/10/2006] [Indexed: 01/07/2023] Open
Abstract
Enlargeosomes are small cytoplasmic vesicles that undergo rapid, Ca2+-dependent exo/endocytosis. The role of the cytoskeleton in these processes was unknown. In PC12-27 cells, microtubule disassembly had little effect on enlargeosomes, whereas microfilament disassembly increased markedly both their resting and stimulated exocytosis, and inhibited their endocytosis. Even at rest enlargeosomes are coated at their cytosolic surface by an actin-associated protein, annexin2, bound by a dual, Ca2+-dependent and Ca2+-independent mechanism. In contrast, the other enlargeosome marker, desmoyokin/Ahnak, is transported across the organelle membrane, apparently by an ABC transporter, and binds to its lumenal face. Annexin2-GFP expression revealed that, upon stimulation, the slow and random enlargeosome movement increases markedly and becomes oriented toward the plasma membrane. After annexin2 downregulation enlargeosome exocytosis induced by both [Ca2+]i rise and cytoskeleton disruption is inhibited, and the NGF-induced differentiation is blocked. Binding of annexin2 to the enlargeosome membrane, the most extensive ever reported (>50% annexin2 bound to approximately 3% of total membrane area), seems therefore to participate in the regulation of their exocytosis.
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Affiliation(s)
- Anna Lorusso
- Scientific Institute San Raffaele, ALEMBIC, Advanced Light and Electron Microscopy BioImaging Center, Milan, Italy
| | - Cesare Covino
- Scientific Institute San Raffaele, ALEMBIC, Advanced Light and Electron Microscopy BioImaging Center, Milan, Italy
| | - Giuseppina Priori
- Department of Neuroscience, Vita-Salute San Raffaele University, Center of Excellence in Cell Development, Milan, Italy
| | - Angela Bachi
- Scientific Institute San Raffaele, ALEMBIC, Advanced Light and Electron Microscopy BioImaging Center, Milan, Italy
| | - Jacopo Meldolesi
- Scientific Institute San Raffaele, ALEMBIC, Advanced Light and Electron Microscopy BioImaging Center, Milan, Italy
- Department of Neuroscience, Vita-Salute San Raffaele University, Center of Excellence in Cell Development, Milan, Italy
- IIT Research Unit of Molecular Neuroscience, Milan, Italy
| | - Evelina Chieregatti
- Department of Neuroscience, Vita-Salute San Raffaele University, Center of Excellence in Cell Development, Milan, Italy
- IIT Research Unit of Molecular Neuroscience, Milan, Italy
- Vita-Salute San Raffaele University, DIBIT, via Olgettina 58, 20132 Milan, Italy. Tel.: +39 022 643 4604; Fax: +39 022 643 4813; E-mail
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288
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Behrens UD, Borde J, Mack AF, Wagner HJ. Distribution of phosphorylated protein kinase C alpha in goldfish retinal bipolar synaptic terminals: control by state of adaptation and pharmacological treatment. Cell Tissue Res 2006; 327:209-20. [PMID: 17043793 DOI: 10.1007/s00441-006-0302-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Accepted: 07/12/2006] [Indexed: 10/24/2022]
Abstract
Protein kinase C (PKC) is a signalling enzyme critically involved in many aspects of synaptic plasticity. In cyprinid retinae, the PKC alpha isoform is localized in a subpopulation of depolarizing bipolar cells that show adaptation-related morphological changes of their axon terminals. We have studied the subcellular localization of phosphorylated PKC alpha (pPKC alpha) in retinae under various conditions by immunohistochemistry with a phosphospecific antibody. In dark-adapted retinae, pPKC alpha immunoreactivity is weak in the cytoplasm of synaptic terminals, labelling being predominantly associated with the membrane compartment. In light-adapted cells, immunoreactivity is diffusely distributed throughout the terminal. Western blot analysis has revealed a reduction of pPKC alpha immunoreactivity in cytosolic fractions of homogenized dark-adapted retinae compared with light-adapted retinae. Pharmacological experiments with the isoform-specific PKC blocker Goe6976 have shown that inhibition of the enzyme influences immunolabelling for pPKC alpha, mimicking the effects of light on the subcellular distribution of immunoreactivity. Our findings suggest that the state of adaptation modifies the subcellular localization of a signalling molecule (PKC alpha) at the ribbon-type synaptic complex. We propose that changes in the subcellular distribution of PKC alpha immunoreactivity might be one component regulating the strength of the signal transfer of the bipolar cell terminal.
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Affiliation(s)
- Uwe D Behrens
- Anatomisches Institut, Oesterbergstrasse 3, 72074, Tübingen, Germany.
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289
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Kraft R, Escobar MM, Narro ML, Kurtis JL, Efrat A, Barnard K, Restifo LL. Phenotypes of Drosophila brain neurons in primary culture reveal a role for fascin in neurite shape and trajectory. J Neurosci 2006; 26:8734-47. [PMID: 16928862 PMCID: PMC6674370 DOI: 10.1523/jneurosci.2106-06.2006] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Subtle cellular phenotypes in the CNS may evade detection by routine histopathology. Here, we demonstrate the value of primary culture for revealing genetically determined neuronal phenotypes at high resolution. Gamma neurons of Drosophila melanogaster mushroom bodies (MBs) are remodeled during metamorphosis under the control of the steroid hormone 20-hydroxyecdysone (20E). In vitro, wild-type gamma neurons retain characteristic morphogenetic features, notably a single axon-like dominant primary process and an arbor of short dendrite-like processes, as determined with microtubule-polarity markers. We found three distinct genetically determined phenotypes of cultured neurons from grossly normal brains, suggesting that subtle in vivo attributes are unmasked and amplified in vitro. First, the neurite outgrowth response to 20E is sexually dimorphic, being much greater in female than in male gamma neurons. Second, the gamma neuron-specific "naked runt" phenotype results from transgenic insertion of an MB-specific promoter. Third, the recessive, pan-neuronal "filagree" phenotype maps to singed, which encodes the actin-bundling protein fascin. Fascin deficiency does not impair the 20E response, but neurites fail to maintain their normal, nearly straight trajectory, instead forming curls and hooks. This is accompanied by abnormally distributed filamentous actin. This is the first demonstration of fascin function in neuronal morphogenesis. Our findings, along with the regulation of human Fascin1 (OMIM 602689) by CREB (cAMP response element-binding protein) binding protein, suggest FSCN1 as a candidate gene for developmental brain disorders. We developed an automated method of computing neurite curvature and classifying neurons based on curvature phenotype. This will facilitate detection of genetic and pharmacological modifiers of neuronal defects resulting from fascin deficiency.
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Affiliation(s)
- Robert Kraft
- Arizona Research Laboratories Division of Neurobiology
| | | | | | | | | | - Kobus Barnard
- Department of Computer Science, and
- Interdisciplinary Program in Cognitive Science, University of Arizona, Tucson, Arizona 85721, and
| | - Linda L. Restifo
- Arizona Research Laboratories Division of Neurobiology
- Interdisciplinary Program in Cognitive Science, University of Arizona, Tucson, Arizona 85721, and
- Department of Neurology, Arizona Health Sciences Center, Tucson, Arizona 85724
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290
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Malacombe M, Bader MF, Gasman S. Exocytosis in neuroendocrine cells: new tasks for actin. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:1175-83. [PMID: 17034880 DOI: 10.1016/j.bbamcr.2006.09.004] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Revised: 08/29/2006] [Accepted: 09/01/2006] [Indexed: 11/19/2022]
Abstract
Most secretory cells undergoing calcium-regulated exocytosis in response to cell surface receptor stimulation display a dense subplasmalemmal actin network, which is remodeled during the exocytotic process. This review summarizes new insights into the role of the cortical actin cytoskeleton in exocytosis. Many earlier findings support the actin-physical-barrier model whereby transient depolymerization of cortical actin filaments permits vesicles to gain access to their appropriate docking and fusion sites at the plasma membrane. On the other hand, data from our laboratory and others now indicate that actin polymerization also plays a positive role in the exocytotic process. Here, we discuss the potential functions attributed to the actin cytoskeleton at each major step of the exocytotic process, including recruitment, docking and fusion of secretory granules with the plasma membrane. Moreover, we present actin-binding proteins, which are likely to link actin organization to calcium signals along the exocytotic pathway. The results cited in this review are derived primarily from investigations of the adrenal medullary chromaffin cell, a cell model that is since many years a source of information concerning the molecular machinery underlying exocytosis.
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Affiliation(s)
- Magali Malacombe
- Département Neurotransmission et Sécrétion Neuroendocrine, Institut des Neurosciences Cellulaires et Intégratives (UMR 7168/LC2), Centre National de la Recherche Scientifique et Université Louis Pasteur, 5 rue Blaise Pascal, 67084 Strasbourg, France
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291
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Charrier C, Ehrensperger MV, Dahan M, Lévi S, Triller A. Cytoskeleton regulation of glycine receptor number at synapses and diffusion in the plasma membrane. J Neurosci 2006; 26:8502-11. [PMID: 16914675 PMCID: PMC6674337 DOI: 10.1523/jneurosci.1758-06.2006] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Lateral diffusion of neurotransmitter receptors in and out of synapses has been postulated as a core mechanism for rapid changes in receptor number at synapses during plastic processes. In this study, we have used single particle tracking to investigate how changes in glycine receptor (GlyR) lateral diffusion properties might account for changes in receptor number at synapses after disruption of the cytoskeleton in dissociated spinal cord neurons. We found that pharmacological disruption of F-actin and microtubules decreased the amount of GlyR and gephyrin, the backbone of the inhibitory postsynaptic scaffold, at synapses. F-actin and microtubule disruption increased GlyR exchanges between the synaptic and extrasynaptic membranes and decreased receptor dwell time at synapses. GlyR lateral diffusion was predominantly controlled by microtubules in the extrasynaptic membrane and by actin at synapses. Both diffusion coefficients and confinement at synapses were affected after F-actin disruption. Our results indicate that receptor exchanges between the synaptic and extrasynaptic compartments depend on the properties of both the postsynaptic differentiation and the extrasynaptic membrane. Consequently, GlyR number at synapses may be rapidly modulated by the cytoskeleton through the regulation of lateral diffusion in the plasma membrane and of receptor stabilization at synapses.
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292
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Yao J, Qi J, Chen G. Actin-dependent activation of presynaptic silent synapses contributes to long-term synaptic plasticity in developing hippocampal neurons. J Neurosci 2006; 26:8137-47. [PMID: 16885227 PMCID: PMC6673772 DOI: 10.1523/jneurosci.1183-06.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Developing neurons have greater capacity in experience-dependent plasticity than adult neurons but the molecular mechanism is not well understood. Here we report a developmentally regulated long-term synaptic plasticity through actin-dependent activation of presynaptic silent synapses in cultured hippocampal neurons. Live FM 1-43 imaging and retrospective immunocytochemistry revealed that many presynaptic boutons in immature neurons are functionally silent at resting conditions, but can be converted into active ones after repetitive neuronal stimulation. The activation of presynaptic silent synapses is dependent on L-type calcium channels and protein kinase A (PKA)/PKC signaling pathways. Moreover, blocking actin polymerization with latrunculin A and cytochalasin B abolishes long-term increase of presynaptic functional boutons induced by repetitive stimulation, whereas actin polymerizer jasplakinolide increases the number of active boutons in immature neurons. In mature neurons, however, presynaptic boutons are mostly functional and repetitive stimulation did not induce additional enhancement. Quantitative immunostaining with phalloidin revealed a significant increase in axonal F-actin level after repetitive stimulation in immature but not mature neurons. These results suggest that actin-dependent activation of presynaptic silent synapses contributes significantly to the long-term synaptic plasticity during neuronal development.
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293
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Chang DTW, Honick AS, Reynolds IJ. Mitochondrial trafficking to synapses in cultured primary cortical neurons. J Neurosci 2006; 26:7035-45. [PMID: 16807333 PMCID: PMC6673923 DOI: 10.1523/jneurosci.1012-06.2006] [Citation(s) in RCA: 302] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Functional synapses require mitochondria to supply ATP and regulate local [Ca2+]i for neurotransmission. Mitochondria are thought to be transported to specific cellular regions of increased need such as synapses. However, little is known about how this occurs, including the spatiotemporal distribution of mitochondria relative to presynaptic and postsynaptic sites, whether mitochondria are dynamically recruited to synapses, and how synaptic activity affects these trafficking patterns. We used primary cortical neurons in culture that form synaptic connections and show spontaneous synaptic activity under normal conditions. Neurons were cotransfected with a mitochondrially targeted cyan fluorescent protein and an enhanced yellow fluorescent protein-tagged synaptophysin or postsynaptic density-95 plasmid to label presynaptic or postsynaptic structures, respectively. Fluorescence microscopy revealed longer dendritic mitochondria that occupied a greater fraction of neuronal process length than axonal mitochondria. Mitochondria were significantly more likely to be localized at synaptic sites. Although this localization was unchanged by inhibition of synaptic activity by tetrodotoxin, it increased in dendritic synapses and decreased in axonal synapses during overactivity by veratridine. Mitochondrial movement and recruitment to synapses also differed between axons and dendrites under basal conditions and when synaptic activity was altered. Additionally, we show that movement of dendritic mitochondria can be selectively impaired by glutamate and zinc. We conclude that mitochondrial trafficking to synapses is dynamic in neurons and is modulated by changes in synaptic activity. Furthermore, mitochondrial morphology and distribution may be optimized differentially to best serve the synaptic distributions in axons and dendrites. Last, selective cessation of mitochondrial movement in dendrites suggests early postsynaptic dysfunction in neuronal injury and degeneration.
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294
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Yano H, Ninan I, Zhang H, Milner TA, Arancio O, Chao MV. BDNF-mediated neurotransmission relies upon a myosin VI motor complex. Nat Neurosci 2006; 9:1009-18. [PMID: 16819522 DOI: 10.1038/nn1730] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Accepted: 05/30/2006] [Indexed: 02/07/2023]
Abstract
Brain-derived neurotrophic factor (BDNF) has been implicated in higher-order cognitive functions and in psychiatric disorders such as depression and schizophrenia. BDNF modulates synaptic transmission and plasticity primarily through the TrkB receptor, but the molecules involved in BDNF-mediated synaptic modulation are largely unknown. Myosin VI (Myo6) is a minus end-directed actin-based motor found in neurons that express Trk receptors. Here we report that Myo6 and a Myo6-binding protein, GIPC1, form a complex that can engage TrkB. Myo6 and GIPC1 were necessary for BDNF-TrkB-mediated facilitation of long-term potentiation in postnatal day 12-13 (P12-13) hippocampus. Moreover, BDNF-mediated enhancement of glutamate release from presynaptic terminals depended not only upon TrkB but also upon Myo6 and GIPC1. Similar defects in basal synaptic transmission as well as presynaptic properties were observed in Myo6 and GIPC1 mutant mice. Together, these results define an important role for the Myo6-GIPC1 motor complex in presynaptic function and in BDNF-TrkB-mediated synaptic plasticity.
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Affiliation(s)
- Hiroko Yano
- Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, Departments of Cell Biology, Physiology and Neuroscience, New York University School of Medicine, 540 First Avenue, New York, New York 10016, USA
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295
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Gundelfinger ED, Boeckers TM, Baron MK, Bowie JU. A role for zinc in postsynaptic density asSAMbly and plasticity? Trends Biochem Sci 2006; 31:366-73. [PMID: 16793273 DOI: 10.1016/j.tibs.2006.05.007] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2006] [Revised: 04/21/2006] [Accepted: 05/25/2006] [Indexed: 01/06/2023]
Abstract
Chemical synapses are asymmetric cell junctions that mediate communication between neurons. Multidomain scaffolding proteins of the Shank family act as major organizing elements of the "postsynaptic density"--that is, the cytoskeletal protein matrix associated with the postsynaptic membrane. A recent study has shown that the C-terminal sterile alpha-motif or "SAM domain" of Shank3 (also known as ProSAP2) can form two-dimensional sheets of helical fibers. Assembly and packaging of these fibers are markedly enhanced by the presence of Zn2+ ions. Zn2+ can be released together with glutamate from synaptic vesicles and can enter the postsynaptic cell through specific ionotropic receptors. Based on these observations, we propose a new model of synaptic plasticity in which Zn2+ influx directly and instantly modulates the structure and function of the postsynaptic density.
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Affiliation(s)
- Eckart D Gundelfinger
- Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Brenneckestrasse 6, 39118 Magdeburg, Germany.
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296
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Shen W, Wu B, Zhang Z, Dou Y, Rao ZR, Chen YR, Duan S. Activity-induced rapid synaptic maturation mediated by presynaptic cdc42 signaling. Neuron 2006; 50:401-14. [PMID: 16675395 DOI: 10.1016/j.neuron.2006.03.017] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 02/14/2006] [Accepted: 03/13/2006] [Indexed: 11/28/2022]
Abstract
Maturation of presynaptic transmitter secretion machinery is a critical step in synaptogenesis. Here we report that a brief train of presynaptic action potentials rapidly converts early nonfunctional contacts between cultured hippocampal neurons into functional synapses by enhancing presynaptic glutamate release. The enhanced release was confirmed by a marked increase in the number of depolarization-induced FM4-64 puncta in the presynaptic axon. This rapid presynaptic maturation can be abolished by treatments that interfered with presynaptic BDNF and Cdc42 signaling or actin polymerization. Activation of Cdc42 by applying BDNF or bradykinin mimicked the effect of electrical activity in promoting synaptic maturation. Furthermore, activity-induced increase in presynaptic actin polymerization, as revealed by increased concentration of actin-YFP at axon boutons, was abolished by inhibiting BDNF and Cdc42 signaling. Thus, rapid presynaptic maturation induced by neuronal activity is mediated by presynaptic activation of the Cdc42 signaling pathway.
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Affiliation(s)
- Wanhua Shen
- Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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297
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Brodin L, Shupliakov O. Giant reticulospinal synapse in lamprey: molecular links between active and periactive zones. Cell Tissue Res 2006; 326:301-10. [PMID: 16786368 DOI: 10.1007/s00441-006-0216-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2006] [Accepted: 04/20/2006] [Indexed: 10/24/2022]
Abstract
Deciphering the function of synaptic release sites is central to understanding neuronal communication. Here, we review studies of the lamprey giant reticulospinal synapse, a model that can be used to dissect synaptic vesicle trafficking at single release sites. The presynaptic axon is large and contains active zones that are spatially separated from each other. During activity, synaptic vesicle membrane is shuttled between the active zone and the periactive zone at which endocytosis occurs. Recent studies have shown that the periactive zone contains an actin-rich cytomatrix that expands during synaptic activity. This cytomatrix has been implicated in multiple functions that include (1) activity-dependent trafficking of proteins between the synaptic vesicle cluster and the periactive zone, (2) synaptic vesicle endocytosis, and (3) the movement of newly formed synaptic vesicles to the vesicle cluster. The actin cytomatrix thus provides a link between the active zone and the periactive zone; this link appears to be critical for sustained cycling of synaptic vesicles.
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Affiliation(s)
- Lennart Brodin
- Department of Neuroscience, CEDB, Karolinska Institutet, S-17177 Stockholm, Sweden.
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298
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Colicos MA, Syed NI. Neuronal networks and synaptic plasticity: understanding complex system dynamics by interfacing neurons with silicon technologies. J Exp Biol 2006; 209:2312-9. [PMID: 16731807 DOI: 10.1242/jeb.02163] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Information processing in the central nervous system is primarily mediated through synaptic connections between neurons. This connectivity in turn defines how large ensembles of neurons may coordinate network output to execute complex sensory and motor functions including learning and memory. The synaptic connectivity between any given pair of neurons is not hard-wired;rather it exhibits a high degree of plasticity, which in turn forms the basis for learning and memory. While there has been extensive research to define the cellular and molecular basis of synaptic plasticity, at the level of either pairs of neurons or smaller networks, analysis of larger neuronal ensembles has proved technically challenging. The ability to monitor the activities of larger neuronal networks simultaneously and non-invasively is a necessary prerequisite to understanding how neuronal networks function at the systems level. Here we describe recent breakthroughs in the area of various bionic hybrids whereby neuronal networks have been successfully interfaced with silicon devices to monitor the output of synaptically connected neurons. These technologies hold tremendous potential for future research not only in the area of synaptic plasticity but also for the development of strategies that will enable implantation of electronic devices in live animals during various memory tasks.
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Affiliation(s)
- Michael A Colicos
- Department of Physiology and Biophysics, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, T2N 4N1, Canada.
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299
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Cristofanilli M, Akopian A. Calcium channel and glutamate receptor activities regulate actin organization in salamander retinal neurons. J Physiol 2006; 575:543-54. [PMID: 16777935 PMCID: PMC1819466 DOI: 10.1113/jphysiol.2006.114108] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Intracellular Ca2+ regulates a variety of neuronal functions, including neurotransmitter release, protein phosphorylation, gene expression and synaptic plasticity. In a variety of cell types, including neurons, Ca2+ is involved in actin reorganization, resulting in either actin polymerization or depolymerization. Very little, however, is known about the relationship between Ca2+ and the actin cytoskeleton organization in retinal neurons. We studied the effect of high-K+-induced depolarization on F-actin organization in salamander retina and found that Ca2+ influx through voltage-gated L-type channels causes F-actin disruption, as assessed by 53 +/- 5% (n = 23, P < 0.001) reduction in the intensity of staining with Alexa-Fluor488-phalloidin, a compound that permits visualization and quantification of polymerized actin. Calcium-induced F-actin depolymerization was attenuated in the presence of protein kinase C antagonists, chelerythrine or bis-indolylmaleimide hydrochloride (GF 109203X). In addition, phorbol 12-myristate 13-acetate (PMA), but not 4alpha-PMA, mimicked the effect of Ca2+ influx on F-actin. Activation of ionotropic AMPA and NMDA glutamate receptors also caused a reduction in F-actin. No effect on F-actin was exerted by caffeine or thapsigargin, agents that stimulate Ca2+ release from internal stores. In whole-cell recording from a slice preparation, light-evoked 'off' but not 'on' EPSCs in 'on-off' ganglion cells were reduced by 60 +/- 8% (n = 8, P < 0.01) by cytochalasin D. These data suggest that elevation of intracellular Ca2+ during excitatory synaptic activity initiates a cascade for activity-dependent actin remodelling, which in turn may serve as a feedback mechanism to attenuate excitotoxic Ca2+ accumulation induced by synaptic depolarization.
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Affiliation(s)
- Massimiliano Cristofanilli
- Department of Ophthalmology, New York University School of Medicine, 550 First Avenue PHL 843, New York, NY 10016, USA
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300
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Majewska AK, Sur M. Plasticity and specificity of cortical processing networks. Trends Neurosci 2006; 29:323-9. [PMID: 16697057 DOI: 10.1016/j.tins.2006.04.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Revised: 03/03/2006] [Accepted: 04/28/2006] [Indexed: 10/24/2022]
Abstract
The cerebral cortex is subdivided into discrete functional areas that are defined by specific properties, including the presence of different cell types, molecular expression patterns, microcircuitry and long-range connectivity. These properties enable different areas of cortex to carry out distinct functions. Emerging data argue that the particular structure and identity of cortical areas derives not only from specific inputs but also from unique processing networks. The aim of this review is to summarize current information on the interplay of intrinsic molecular cues with activity patterns that are driven by sensory experience and shape cortical networks as they develop, emphasizing synaptic connections in networks that process vision. This review is part of the TINS special issue on The Neural Substrates of Cognition.
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Affiliation(s)
- Ania K Majewska
- Department of Neurobiology and Anatomy, University of Rochester Medical Center, Rochester, NY 14642, USA.
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