201
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Hanley JG. AMPA receptor trafficking pathways and links to dendritic spine morphogenesis. Cell Adh Migr 2008; 2:276-82. [PMID: 19262155 DOI: 10.4161/cam.2.4.6510] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Affiliation(s)
- Jonathan G Hanley
- MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, Bristol, UK.
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202
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Bourne JN, Harris KM. Balancing structure and function at hippocampal dendritic spines. Annu Rev Neurosci 2008; 31:47-67. [PMID: 18284372 DOI: 10.1146/annurev.neuro.31.060407.125646] [Citation(s) in RCA: 669] [Impact Index Per Article: 41.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Dendritic spines are the primary recipients of excitatory input in the central nervous system. They provide biochemical compartments that locally control the signaling mechanisms at individual synapses. Hippocampal spines show structural plasticity as the basis for the physiological changes in synaptic efficacy that underlie learning and memory. Spine structure is regulated by molecular mechanisms that are fine-tuned and adjusted according to developmental age, level and direction of synaptic activity, specific brain region, and exact behavioral or experimental conditions. Reciprocal changes between the structure and function of spines impact both local and global integration of signals within dendrites. Advances in imaging and computing technologies may provide the resources needed to reconstruct entire neural circuits. Key to this endeavor is having sufficient resolution to determine the extrinsic factors (such as perisynaptic astroglia) and the intrinsic factors (such as core subcellular organelles) that are required to build and maintain synapses.
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Affiliation(s)
- Jennifer N Bourne
- Center for Learning and Memory, Department of Neurobiology, University of Texas, Austin, Texas 78712-0805, USA.
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203
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Edwards CM, Mundy GR. Eph receptors and ephrin signaling pathways: a role in bone homeostasis. Int J Med Sci 2008; 5:263-72. [PMID: 18797510 PMCID: PMC2536716 DOI: 10.7150/ijms.5.263] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Accepted: 09/03/2008] [Indexed: 02/05/2023] Open
Abstract
The maintenance of bone homeostasis is tightly controlled, and largely dependent upon cellular communication between osteoclasts and osteoblasts, and the coupling of bone resorption to bone formation. This tight coupling is essential for the correct function and maintenance of the skeletal system, repairing microscopic skeletal damage and replacing aged bone. A range of pathologic diseases, including osteoporosis and cancer-induced bone disease, disrupt this coupling and cause subsequent alterations in bone homeostasis. Eph receptors and their associated ligands, ephrins, play critical roles in a number of cellular processes including immune regulation, neuronal development and cancer metastasis. Eph receptors are also expressed by cells found within the bone marrow microenvironment, including osteoclasts and osteoblasts, and there is increasing evidence to implicate this family of receptors in the control of normal and pathological bone remodeling.
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Affiliation(s)
- Claire M Edwards
- Vanderbilt Center for Bone Biology, Departments of Cancer Biology and Clinical Pharmacology/Medicine, Vanderbilt University, Nashville, TN 37232-0575, USA.
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204
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EphB receptors couple dendritic filopodia motility to synapse formation. Neuron 2008; 59:56-69. [PMID: 18614029 DOI: 10.1016/j.neuron.2008.05.007] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2007] [Revised: 04/18/2008] [Accepted: 05/08/2008] [Indexed: 12/31/2022]
Abstract
Motile dendritic filopodial processes are thought to be precursors of spine synapses, but how motility relates to cell-surface cues required for axon-dendrite recognition and synaptogenesis remains unclear. We demonstrate with dynamic imaging that loss of EphBs results in reduced motility of filopodia in cultured cortical neurons and brain slice. EphB knockdown and rescue experiments during different developmental time windows show that EphBs are required for synaptogenesis only when filopodia are most abundant and motile. In the context of EphB knockdown and reduced filopodia motility, independent rescue of either motility with PAK or of Eph-ephrin binding with an EphB2 kinase mutant is not sufficient to restore synapse formation. Strikingly, the combination of PAK and kinase-inactive EphB2 rescues synaptogenesis. Deletion of the ephrin-binding domain from EphB2 precludes rescue, indicating that both motility and trans-cellular interactions are required. Our findings provide a mechanistic link between dendritic filopodia motility and synapse differentiation.
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205
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Causeret F, Terao M, Jacobs T, Nishimura YV, Yanagawa Y, Obata K, Hoshino M, Nikolic M. The p21-activated kinase is required for neuronal migration in the cerebral cortex. ACTA ACUST UNITED AC 2008; 19:861-75. [PMID: 18701438 DOI: 10.1093/cercor/bhn133] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The normal formation and function of the mammalian cerebral cortex depend on the positioning of its neurones, which occurs in a highly organized, layer-specific manner. The correct morphology and movement of neurones rely on synchronized regulation of their actin filaments and microtubules. The p21-activated kinase (Pak1), a key cytoskeletal regulator, controls neuronal polarization, elaboration of axons and dendrites, and the formation of dendritic spines. However, its in vivo role in the developing nervous system is unclear. We have utilized in utero electroporation into mouse embryo cortices to reveal that both loss and gain of Pak1 function affect radial migration of projection neurones. Overexpression of hyperactivated Pak1 predominantly caused neurones to arrest in the intermediate zone (IZ) with apparently misoriented and disorganized leading projections. Loss of Pak1 disrupted the morphology of migrating neurones, which accumulated in the IZ and deep cortical layers. Unexpectedly, a significant number of neurones with reduced Pak1 expression aberrantly entered into the normally cell-sparse marginal zone, suggesting their inability to cease migrating that may be due to their impaired dissociation from radial glia. Our findings reveal the in vivo importance of temporal and spatial regulation of the Pak1 kinase during key stages of cortical development.
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Affiliation(s)
- Frédéric Causeret
- Department of Cellular and Molecular Neuroscience, Imperial College School of Medicine, London, UK
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206
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Penzes P, Cahill ME, Jones KA, Srivastava DP. Convergent CaMK and RacGEF signals control dendritic structure and function. Trends Cell Biol 2008; 18:405-13. [PMID: 18701290 DOI: 10.1016/j.tcb.2008.07.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 06/30/2008] [Accepted: 07/02/2008] [Indexed: 12/25/2022]
Abstract
Structural plasticity of excitatory synapses is a vital component of neuronal development, synaptic plasticity and behavior, and its malfunction underlies many neurodevelopmental and psychiatric disorders. However, the molecular mechanisms that control dendritic spine morphogenesis have only recently emerged. We summarize recent work that has revealed an important connection between calcium/calmodulin-dependent kinases (CaMKs) and guanine-nucleotide-exchange factors (GEFs) that activate the small GTPase Rac (RacGEFs) in controlling dendritic spine morphogenesis. These two groups of molecules function in neurons as a unique signaling cassette that transduces calcium influx into small GTPase activity and, thence, actin reorganization and spine morphogenesis. Through this pathway, CaMKs and RacGEFs amplify calcium signals and translate them into spatially and temporally regulated structural remodeling of dendritic spines.
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Affiliation(s)
- Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Avenue, Chicago, IL 60611, USA.
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207
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Penzes P, Jones KA. Dendritic spine dynamics--a key role for kalirin-7. Trends Neurosci 2008; 31:419-27. [PMID: 18597863 PMCID: PMC3973420 DOI: 10.1016/j.tins.2008.06.001] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 05/23/2008] [Accepted: 06/02/2008] [Indexed: 11/20/2022]
Abstract
Changes in the structure and function of dendritic spines contribute to numerous physiological processes such as synaptic transmission and plasticity, as well as behavior, including learning and memory. Moreover, altered dendritic spine morphogenesis and plasticity is an endophenotype of many neurodevelopmental and neuropsychiatric disorders. Hence, the molecular mechanisms that control spine plasticity and pathology have been under intense investigation over the past few years. A series of recent studies has improved our understanding of spine dynamics by establishing kalirin-7 as an important regulator of dendritic spine development as well as structural and functional plasticity, providing a model for the molecular control of structural plasticity and implicating kalirin-7 in synaptic pathology in several disorders including schizophrenia and Alzheimer's disease.
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Affiliation(s)
- Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
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208
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The Pak1 kinase: an important regulator of neuronal morphology and function in the developing forebrain. Mol Neurobiol 2008; 37:187-202. [PMID: 18649038 DOI: 10.1007/s12035-008-8032-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 06/04/2008] [Indexed: 01/07/2023]
Abstract
The mammalian central nervous system (CNS) represents a highly complex unit, the correct function of which relies on the appropriate differentiation and survival of its neurones. It is becoming apparent that the Rho family of small GTPases and their downstream targets have a major function in regulating CNS development. Among the effectors, the role of the Pak family of kinases, especially Pak1, is becoming increasingly evident. Although highest levels of Pak1 expression and activation are detected in the developing nervous system, much remains undiscovered concerning its function in neurones. This review summarises what is currently known regarding the biological and molecular role of Pak1 in the mammalian forebrain. It emphasises the importance of Pak1 in regulating neuronal polarity, morphology, migration and synaptic function. Consequently, there are also strong indications that Pak1 is required for normal cognitive function. Furthermore, loss of Pak1 has been associated with the progression of neurodegenerative disorders, particularly Alzheimer's disease, while up-regulation and de-regulation may be responsible for oncogenic transformation of support cells within the CNS, especially astrocyte progenitors. Together, these new and exciting findings encourage the future exploration into the function of Pak1 in the nervous system, thus, paving the way for novel strategies towards improved diagnosis and therapeutic treatment of diseases that affect the CNS.
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209
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Xin X, Wang Y, Ma XM, Rompolas P, Keutmann HT, Mains RE, Eipper BA. Regulation of Kalirin by Cdk5. J Cell Sci 2008; 121:2601-11. [PMID: 18628310 DOI: 10.1242/jcs.016089] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Kalirin, one of the few Rho guanine nucleotide exchange factors (GEFs) that contains spectrin-like repeats, plays a critical role in axon extension and maintenance of dendritic spines. PC12 cells were used to determine whether Cdk5, a critical participant in both processes, regulates the action of Kalirin. Expression of Kalirin-7 in nondifferentiated PC12 cells caused GEF-activity-dependent extension of broad cytoplasmic protrusions; coexpression of dominant-negative Cdk5 largely eliminated this response. The spectrin-like repeat region of Kalirin plays an essential role in this response, which is not mimicked by the GEF domain alone. Thr1590, which follows the first GEF domain of Kalirin, is the only Cdk5 phosphorylation site in Kalirin-7. Although mutant Kalirin-7 with Ala1590 retains GEF activity, it is unable to cause extension of protrusions. Kalirin-7 with an Asp1590 mutation has slightly increased GEF activity and dominant-negative Cdk5 fails to block its ability to cause extension of protrusions. Phosphorylation of Thr1590 causes a slight increase in GEF activity and Kalirin-7 solubility. Dendritic spines formed by cortical neurons in response to the expression of Kalirin-7 with Ala1590 differ in shape from those formed in response to wild-type Kalirin-7 or Kalirin-7 containing Asp1590. The presence of Thr1590 in each major Kalirin isoform would allow Cdk5 to regulate Kalirin function throughout development.
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Affiliation(s)
- Xiaonan Xin
- Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3401, USA
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210
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Harrington AW, Li QM, Tep C, Park JB, He Z, Yoon SO. The role of Kalirin9 in p75/nogo receptor-mediated RhoA activation in cerebellar granule neurons. J Biol Chem 2008; 283:24690-7. [PMID: 18625710 DOI: 10.1074/jbc.m802188200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
p75 and the Nogo receptor form a signaling unit for myelin inhibitory molecules, with p75 being responsible for RhoA activation. Because p75 lacks the GDP/GTP exchange factor domain, it has remained unclear how p75 activates RhoA. Here, we report that Kalirin9, a dual RhoGEF, binds p75 directly and regulates p75-Nogo receptor-dependent RhoA activation and neurite inhibition in response to myelin-associated glycoprotein. The region of p75 that Kalirin9 binds includes its mastoparan-like fifth helix, which was shown to recruit RhoGDI-RhoA. As predicted from the presence of a shared binding site, we found that Kalirin9 competes with RhoGDI for p75 binding in a dose-dependent manner in vitro. In line with these data, myelin-associated glycoprotein addition to cerebellar granule neurons resulted in a reduction in the association of Kalirin9 with p75, and a simultaneous increase in the binding of RhoGDI to p75. These results reveal a mechanism by which the fifth helix of p75 regulates RhoA activation.
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Affiliation(s)
- Anthony W Harrington
- Department of Molecular and Cellular Biochemistry, Center for Molecular Neurobiology, The Ohio State University, Columbus, Ohio 43210, USA
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211
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Abstract
Remodeling of central excitatory synapses is crucial for synapse maturation and plasticity, and contributes to neurodevelopmental and psychiatric disorders. Remodeling of dendritic spines and the associated synapses has been postulated to require the coordination of adhesion with spine morphology and stability; however, the molecular mechanisms that functionally link adhesion molecules with regulators of dendritic spine morphology are mostly unknown. Here, we report that spine size and N-cadherin content are tightly coordinated. In rat mature cortical pyramidal neurons, N-cadherin-dependent adhesion modulates the morphology of existing spines by recruiting the Rac1 guanine-nucleotide exchange factor kalirin-7 to synapses through the scaffolding protein AF-6/afadin. In pyramidal neurons, N-cadherin, AF-6, and kalirin-7 colocalize at synapses and participate in the same multiprotein complexes. N-cadherin clustering promotes the reciprocal interaction and recruitment of N-cadherin, AF-6, and kalirin-7, increasing the content of Rac1 and in spines and PAK (p21-activated kinase) phosphorylation. N-cadherin-dependent spine enlargement requires AF-6 and kalirin-7 function. Conversely, disruption of N-cadherin leads to thin, long spines, with reduced Rac1 contact, caused by uncoupling of N-cadherin, AF-6, and kalirin-7 from each other. By dynamically linking N-cadherin with a regulator of spine plasticity, this pathway allows synaptic adhesion molecules to rapidly coordinate spine remodeling associated with synapse maturation and plasticity. This study hence identifies a novel mechanism whereby cadherins, a major class of synaptic adhesion molecules, signal to the actin cytoskeleton to control the morphology of dendritic spines, and outlines a mechanism that underlies the coordination of synaptic adhesion with spine morphology.
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212
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Muly EC, Nairn AC, Greengard P, Rainnie DG. Subcellular distribution of the Rho-GEF Lfc in primate prefrontal cortex: effect of neuronal activation. J Comp Neurol 2008; 508:927-39. [PMID: 18399541 DOI: 10.1002/cne.21703] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The strength of synaptic connections in the brain varies with activity, and this plasticity depends on remodeling of the actin cytoskeleton in dendritic spines. Critical to this are the Rho family GTPases, whose activity is controlled by various modulatory proteins, including the Rho-GEF Lfc. In cultured neurons and nonneuronal cells, Lfc has been shown both to bind to microtubules and to regulate the actin cytoskeleton. Significantly, Lfc was found to be concentrated in the dendritic shafts of cultured hippocampal neurons under control conditions but then translocated into spines when neural activity was stimulated. In this study, we used immunohistochemistry and electron microscopy to examine activity-dependent changes in the distribution of Lfc in the neuropil of monkey prefrontal cortex. We found that, although Lfc was concentrated in dendrites, it also had a complex distribution in the neuropil, including being present in spines, axons, terminals, and glial processes. Moreover, Lfc distribution varied in different layers of cortex. By using an in vitro slice preparation of monkey prefrontal cortex, we demonstrated an activity-dependent translocation of Lfc from dendritic shafts to spines. The results of this study support a role for Lfc in activity-dependent spine plasticity and demonstrate the feasibility of studying activity-dependent changes in protein localization in tissue slices.
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Affiliation(s)
- E Chris Muly
- Department of Psychiatry and Behavioral Sciences, Yerkes National Primate Research Center, Atlanta, Georgia 30322, USA.
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213
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An activity-regulated microRNA controls dendritic plasticity by down-regulating p250GAP. Proc Natl Acad Sci U S A 2008; 105:9093-8. [PMID: 18577589 DOI: 10.1073/pnas.0803072105] [Citation(s) in RCA: 453] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Activity-regulated gene expression is believed to play a key role in the development and refinement of neuronal circuitry. Nevertheless, the transcriptional networks that regulate synapse growth and plasticity remain largely uncharacterized. Here, we show that microRNA 132 (miR132) is an activity-dependent rapid response gene regulated by the cAMP response element-binding (CREB) protein pathway. Introduction of miR132 into hippocampal neurons enhanced dendrite morphogenesis whereas inhibition of miR132 by 2'O-methyl RNA antagonists blocked these effects. Furthermore, neuronal activity inhibited translation of p250GAP, a miR132 target, and siRNA-mediated knockdown of p250GAP mimicked miR132-induced dendrite growth. Experiments using dominant-interfering mutants suggested that Rac signaling is downstream of miR132 and p250GAP. We propose that the miR132-p250GAP pathway plays a key role in activity-dependent structural and functional plasticity.
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214
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Yohe ME, Rossman K, Sondek J. Role of the C-terminal SH3 domain and N-terminal tyrosine phosphorylation in regulation of Tim and related Dbl-family proteins. Biochemistry 2008; 47:6827-39. [PMID: 18537266 DOI: 10.1021/bi702543p] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Dbl-related oncoproteins are guanine nucleotide exchange factors (GEFs) specific for Rho-family GTPases and typically possess tandem Dbl (DH) and pleckstrin homology (PH) domains that act in concert to catalyze exchange. Although the exchange potential of many Dbl-family proteins is constitutively activated by truncation, the precise mechanisms of regulation for many Dbl-family proteins are unknown. Tim and Vav are distantly related Dbl-family proteins that are similarly regulated; their Dbl homology (DH) domains interact with N-terminal helices to exclude and prevent activation of Rho GTPases. Phosphorylation, substitution, or deletion of the blocking helices relieves this autoinhibition. Here we show that two other Dbl-family proteins, Ngef and Wgef, which like Tim contain a C-terminal SH3 domain, are also activated by tyrosine phosphorylation of a blocking helix. Consequently, basal autoinhibition of DH domains by direct steric exclusion using short N-terminal helices likely represents a conserved mechanism of regulation for the large family of Dbl-related proteins. N-Terminal truncation or phosphorylation of many other Dbl-family GEFs leads to their activation; similar autoinhibition mechanisms could explain some of these events. In addition, we show that the C-terminal SH3 domain binding to a polyproline region N-terminal to the DH domain of the Tim subgroup of Dbl-family proteins provides a unique mechanism of regulated autoinhibition of exchange activity that is functionally linked to the interactions between the autoinhibitory helix and the DH domain.
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Affiliation(s)
- Marielle E Yohe
- Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA
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215
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Schiller MR, Ferraro F, Wang Y, Ma XM, McPherson CE, Sobota JA, Schiller NI, Mains RE, Eipper BA. Autonomous functions for the Sec14p/spectrin-repeat region of Kalirin. Exp Cell Res 2008; 314:2674-91. [PMID: 18585704 DOI: 10.1016/j.yexcr.2008.05.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 05/16/2008] [Accepted: 05/16/2008] [Indexed: 01/22/2023]
Abstract
Kalirin is a GDP/GTP exchange factor (GEF) for Rho proteins that modulates the actin cytoskeleton in neurons. Alternative splicing generates Delta-isoforms, which encode the RhoGEF domain, but lack the N-terminal Sec14p domain and first 4 spectrin-like repeats of the full-length isoforms. Splicing has functional consequences, with Kal7 but not DeltaKal7 causing formation of dendritic spines. Cells lacking endogenous Kalirin were used to explore differences between these splice variants. Expression of DeltaKal7 in this system induces extensive lamellipodial sheets, while expression of Kal7 induces formation of adherent compact, round cells with abundant cortical actin. Based on in vitro and cell-based assays, Kal7 and DeltaKal7 are equally active GEFs, suggesting that other domains are involved in controlling cell morphology. Catalytically inactive Kal7 and a Kalirin fragment which includes only Sec14p and spectrin-like domains retain the ability to produce compact, round cells and fractionate as high molecular weight complexes. Separating the Sec14p domain from the spectrin-like repeats eliminates the ability of Kal7 to cause this response. The isolated Sec14p domain binds PI(3,5)P2 and PI3P, but does not alter cell morphology. We conclude that the Sec14p and N-terminal spectrin-like domains of Kalirin play critical roles in distinguishing the actions of full-length and Delta-Kalirin proteins.
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Affiliation(s)
- Martin R Schiller
- Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030, USA.
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216
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Abstract
Bidirectional signaling has emerged as an important signature by which Ephs and ephrins control biological functions. Eph/ephrin signaling participates in a wide spectrum of developmental processes, and cross-regulation with other communication pathways lies at the heart of the complexity underlying their function in vivo. Here, we review in vitro and in vivo data describing molecular, functional, and genetic interactions between Eph/ephrin and other cell surface signaling pathways. The complexity of Eph/ephrin function is discussed in terms of the pathways that regulate Eph/ephrin signaling and also the pathways that are regulated by Eph/ephrin signaling.
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Affiliation(s)
- Dina Arvanitis
- Université de Toulouse, Centre de Biologie du Développement, 31062 Toulouse cedex 9, France
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217
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Rapid loss of dendritic spines after stress involves derangement of spine dynamics by corticotropin-releasing hormone. J Neurosci 2008; 28:2903-11. [PMID: 18337421 DOI: 10.1523/jneurosci.0225-08.2008] [Citation(s) in RCA: 197] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Chronic stress causes dendritic regression and loss of dendritic spines in hippocampal neurons that is accompanied by deficits in synaptic plasticity and memory. However, the responsible mechanisms remain unresolved. Here, we found that within hours of the onset of stress, the density of dendritic spines declined in vulnerable dendritic domains. This rapid, stress-induced spine loss was abolished by blocking the receptor (CRFR(1)) of corticotropin-releasing hormone (CRH), a hippocampal neuropeptide released during stress. Exposure to CRH provoked spine loss and dendritic regression in hippocampal organotypic cultures, and selective blockade of the CRFR(1) receptor had the opposite effect. Live, time-lapse imaging revealed that CRH reduced spine density by altering dendritic spine dynamics: the peptide selectively and reversibly accelerated spine retraction, and this mechanism involved destabilization of spine F-actin. In addition, mice lacking the CRFR(1) receptor had augmented spine density. These findings support a mechanistic role for CRH-CRFR(1) signaling in stress-evoked spine loss and dendritic remodeling.
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218
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Saneyoshi T, Wayman G, Fortin D, Davare M, Hoshi N, Nozaki N, Natsume T, Soderling TR. Activity-dependent synaptogenesis: regulation by a CaM-kinase kinase/CaM-kinase I/betaPIX signaling complex. Neuron 2008; 57:94-107. [PMID: 18184567 DOI: 10.1016/j.neuron.2007.11.016] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2007] [Revised: 08/17/2007] [Accepted: 11/21/2007] [Indexed: 01/04/2023]
Abstract
Neuronal activity augments maturation of mushroom-shaped spines to form excitatory synapses, thereby strengthening synaptic transmission. We have delineated a Ca(2+)-signaling pathway downstream of the NMDA receptor that stimulates calmodulin-dependent kinase kinase (CaMKK) and CaMKI to promote formation of spines and synapses in hippocampal neurons. CaMKK and CaMKI form a multiprotein signaling complex with the guanine nucleotide exchange factor (GEF) betaPIX and GIT1 that is localized in spines. CaMKI-mediated phosphorylation of Ser516 in betaPIX enhances its GEF activity, resulting in activation of Rac1, an established enhancer of spinogenesis. Suppression of CaMKK or CaMKI by pharmacological inhibitors, dominant-negative (dn) constructs and siRNAs, as well as expression of the betaPIX Ser516Ala mutant, decreases spine formation and mEPSC frequency. Constitutively-active Pak1, a downstream effector of Rac1, rescues spine inhibition by dnCaMKI or betaPIX S516A. This activity-dependent signaling pathway can promote synapse formation during neuronal development and in structural plasticity.
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Affiliation(s)
- Takeo Saneyoshi
- Vollum Institute, Oregon Health and Sciences University, Portland, OR 97239, USA
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219
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Abstract
Synchronized control of excitatory and inhibitory synapse maturation is crucial for normal brain wiring, while its dysfunction leads to neurodevelopmental disorders, including autism. A paper in this issue of Neuron identified a novel role for the KCC2 pump, also responsible for the GABAergic synapse developmental switch, in regulating spiny excitatory synapse maturation, implicating it in the coordinated maturation of inhibitory and excitatory synapses.
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220
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Ma QL, Yang F, Calon F, Ubeda OJ, Hansen JE, Weisbart RH, Beech W, Frautschy SA, Cole GM. p21-activated kinase-aberrant activation and translocation in Alzheimer disease pathogenesis. J Biol Chem 2008; 283:14132-43. [PMID: 18347024 DOI: 10.1074/jbc.m708034200] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Defects in dendritic spines and synapses contribute to cognitive deficits in mental retardation syndromes and, potentially, Alzheimer disease. p21-activated kinases (PAKs) regulate actin filaments and morphogenesis of dendritic spines regulated by the Rho family GTPases Rac and Cdc42. We previously reported that active PAK was markedly reduced in Alzheimer disease cytosol, accompanied by downstream loss of the spine actin-regulatory protein Drebrin. beta-Amyloid (Abeta) oligomer was implicated in PAK defects. Here we demonstrate that PAK is aberrantly activated and translocated from cytosol to membrane in Alzheimer disease brain and in 22-month-old Tg2576 transgenic mice with Alzheimer disease. This active PAK coimmunoprecipitated with the small GTPase Rac and both translocated to granules. Abeta42 oligomer treatment of cultured hippocampal neurons induced similar effects, accompanied by reduction of dendrites that were protected by kinase-active but not kinase-dead PAK. Abeta42 oligomer treatment also significantly reduced N-methyl-d-aspartic acid receptor subunit NR2B phosphotyrosine labeling. The Src family tyrosine kinase inhibitor PP2 significantly blocked the PAK/Rac translocation but not the loss of p-NR2B in Abeta42 oligomer-treated neurons. Src family kinases are known to phosphorylate the Rac activator Tiam1, which has recently been shown to be Abeta-responsive. In addition, anti-oligomer curcumin comparatively suppressed PAK translocation in aged Tg2576 transgenic mice with Alzheimer amyloid pathology and in Abeta42 oligomer-treated cultured hippocampal neurons. Our results implicate aberrant PAK in Abeta oligomer-induced signaling and synaptic deficits in Alzheimer disease.
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Affiliation(s)
- Qiu-Lan Ma
- Department of Medicine, UCLA, Los Angeles, California, USA
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221
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Reber M, Hindges R, Lemke G. Eph receptors and ephrin ligands in axon guidance. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 621:32-49. [PMID: 18269209 DOI: 10.1007/978-0-387-76715-4_3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Michael Reber
- INSERM U.575, Centre de Neurochimie, 5, rue Blaise Pascal, 67084 Strasbourg, France.
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222
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Nakazawa T, Kuriu T, Tezuka T, Umemori H, Okabe S, Yamamoto T. Regulation of dendritic spine morphology by an NMDA receptor-associated Rho GTPase-activating protein, p250GAP. J Neurochem 2008; 105:1384-93. [PMID: 18331582 DOI: 10.1111/j.1471-4159.2008.05335.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The NMDA receptor regulates spine morphological plasticity by modulating Rho GTPases. However, the molecular mechanisms for NMDA receptor-mediated regulation of Rho GTPases remain elusive. In this study, we show that p250GAP, an NMDA receptor-associated RhoGAP, regulates spine morphogenesis by modulating RhoA activity. Knock-down of p250GAP increased spine width and elevated the endogenous RhoA activity in primary hippocampal neurons. The increased spine width by p250GAP knock-down was suppressed by the expression of a dominant-negative form of RhoA. Furthermore, p250GAP is involved in NMDA receptor-mediated RhoA activation. In response to NMDA receptor activation, exogenously expressed green fluorescent protein (GFP)-tagged p250GAP was redistributed. Thus, these data suggest that p250GAP plays an important role in NMDA receptor-mediated regulation of RhoA activity leading to spine morphological plasticity.
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Affiliation(s)
- Takanobu Nakazawa
- Division of Oncology, Department of Cancer Biology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan
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223
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de Curtis I. Functions of Rac GTPases during neuronal development. Dev Neurosci 2008; 30:47-58. [PMID: 18075254 DOI: 10.1159/000109851] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2006] [Accepted: 02/27/2007] [Indexed: 12/11/2022] Open
Abstract
The small GTPases of the Rho family are important regulators of the actin cytoskeleton and are critical for several aspects of neuronal development including the establishment of neuronal polarity, extension of axon and dendrites, neurite branching, axonal navigation and synapse formation. The aim of this review is to present evidence supporting the function of Rac and Rac-related proteins in different aspects of neuronal maturation, based on work performed with organisms including nematodes, Drosophila, Xenopus and mice, and with primary cultures of developing neurons. Three of the 4 vertebrate Rac-related genes, namely Rac1, Rac3 and RhoG, are expressed in the nervous system, and several data support an essential role of all 3 GTPases in distinct aspects of neuronal development and function. Two important points emerge from the analysis presented: highly homologous Rac-related proteins may perform different functions in the developing nervous system; on the other hand, the data also indicate that similar GTPases may perform redundant functions in vivo.
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Affiliation(s)
- Ivan de Curtis
- Cell Adhesion Unit, San Raffaele Scientific Institute, Milan, Italy.
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224
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Lim BK, Matsuda N, Poo MM. Ephrin-B reverse signaling promotes structural and functional synaptic maturation in vivo. Nat Neurosci 2008; 11:160-9. [PMID: 18193042 DOI: 10.1038/nn2033] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Accepted: 12/04/2007] [Indexed: 11/09/2022]
Abstract
Ephrin-Eph signaling is involved in axon guidance during development, but it may also regulate synapse development after the axon has contacted the target cell. Here we report that the activation of ephrin-B reverse signaling in the developing Xenopus laevis optic tectum promotes morphological and functional maturation of retinotectal synapses. Elevation of ephrin-B signaling increased the number of retinotectal synapses and stabilized the axon arbors of retinal ganglion cells. It also enhanced basal synaptic transmission and activity-induced long-term potentiation (LTP) of retinotectal synapses. The functional effects were caused by a rapid enhancement of presynaptic glutamate release and a delayed increase in the postsynaptic glutamate responsiveness. The facilitated LTP induction occurred during the early phase of enhanced transmitter release and appeared to be causally related to the late-phase postsynaptic maturation via an NMDA receptor-dependent mechanism. This ephrin-B-dependent synapse maturation supports the notion that the ephrin/Eph protein families have multiple functions in neural development.
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Affiliation(s)
- Byung Kook Lim
- Division of Neurobiology, Department of Molecular and Cell Biology, Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720-3200, USA
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225
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Costain WJ, Rasquinha I, Sandhu JK, Rippstein P, Zurakowski B, Slinn J, MacManus JP, Stanimirovic DB. Cerebral ischemia causes dysregulation of synaptic adhesion in mouse synaptosomes. J Cereb Blood Flow Metab 2008; 28:99-110. [PMID: 17519975 DOI: 10.1038/sj.jcbfm.9600510] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Synaptic pathology is observed during hypoxic events in the central nervous system in the form of altered dendrite structure and conductance changes. These alterations are rapidly reversible, on the return of normoxia, but are thought to initiate subsequent neuronal cell death. To characterize the effects of hypoxia on regulators of synaptic stability, we examined the temporal expression of cell adhesion molecules (CAMs) in synaptosomes after transient middle cerebral artery occlusion (MCAO) in mice. We focused on events preceding the onset of ischemic neuronal cell death (<48 h). Synaptosome preparations were enriched in synaptically localized proteins and were free of endoplasmic reticulum and nuclear contamination. Electron microscopy showed that the synaptosome preparation was enriched in spheres (approximately 650 nm in diameter) containing secretory vesicles and postsynaptic densities. Forebrain mRNA levels of synaptically located CAMs was unaffected at 3 h after MCAO. This is contrasted by the observation of consistent downregulation of synaptic CAMs at 20 h after MCAO. Examination of synaptosomal CAM protein content indicated that certain adhesion molecules were decreased as early as 3 h after MCAO. For comparison, synaptosomal Agrn protein levels were unaffected by cerebral ischemia. Furthermore, a marked increase in the levels of p-Ctnnb1 in ischemic synaptosomes was observed. p-Ctnnb1 was detected in hippocampal fiber tracts and in cornu ammonis 1 neuronal nuclei. These results indicate that ischemia induces a dysregulation of a subset of synaptic proteins that are important regulators of synaptic plasticity before the onset of ischemic neuronal cell death.
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Affiliation(s)
- Willard J Costain
- Glycosyltransferase and Neuroglycomics, Institute for Biological Sciences, National Research Council, Ottawa, Ontario, Canada.
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226
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Abstract
Ephrin (Eph) signaling via Eph receptors affects neuronal structure and function. We report here that exogenous ephrinAs (EphAs) induce outgrowth of filopodial processes from astrocytes within minutes in rat hippocampal slice cultures. Identical effects were induced by release of endogenous ephrinAs by cleavage of their glycosylphosphatidylinositol anchor. Reverse transcription-PCR and immunocytochemistry revealed the expression of multiple EphA receptors (EphARs) in astrocytes. Exogenous and endogenous ephrins did not induce process outgrowth from astrocytes transfected with a kinase-dead EphAR construct, indicating that the critical EphARs were located on glia. Concomitant with these morphological changes, ephrinA reduced the frequency of (S)-3,5-dihydroxyphenylglycine-evoked NMDA receptor-mediated inward currents in CA1 pyramidal cells, elicited by release of glutamate from glial cells. The sensitivity of CA1 cell synaptic or extrasynaptic NMDA receptors was unaffected by ephrinA, indicating that this effect was mediated by inhibition of glutamate release from glial cells. Finally, ephrinA application decreased the frequency and increased the duration of spontaneous oscillations of the intracellular [Ca2+] in astrocytes. We conclude that ephrinA-EphA signaling is a pluripotent regulator of neuron-astrocyte interactions mediating rapid structural and functional plasticity.
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227
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Nathalie Lacor P. Advances on the understanding of the origins of synaptic pathology in AD. Curr Genomics 2007; 8:486-508. [PMID: 19415125 PMCID: PMC2647163 DOI: 10.2174/138920207783769530] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 12/20/2007] [Accepted: 12/20/2007] [Indexed: 12/14/2022] Open
Abstract
Although Alzheimer's disease (AD) was first discovered a century ago, we are still facing a lack of definitive diagnosis during the patient's lifetime and are unable to prescribe a curative treatment. However, the past 10 years have seen a "revamping" of the main hypothesis about AD pathogenesis and the hope to foresee possible treatment. AD is no longer considered an irreversible disease. A major refinement of the classic beta-amyloid cascade describing amyloid fibrils as neurotoxins has been made to integrate the key scientific evidences demonstrating that the first pathological event occurring in AD early stages affects synaptic function and maintenance. A concept fully compatible with synapse loss being the best pathological correlate of AD rather than other described neuropathological hallmarks (amyloid plaques, neurofibrillary tangles or neuronal death). The notion that synaptic alterations might be reverted, thus offering a potential curability, was confirmed by immunotherapy experiments targeting beta-amyloid protein in transgenic AD mice in which cognitive functions were improved despite no reduction in the amyloid plaques burden. The updated amyloid cascade now integrates the synapse failure triggered by soluble Abeta-oligomers. Still no consensus has been reached on the most toxic Abeta conformations, neither on their site of production nor on their extra- versus intra-cellular actions. Evidence shows that soluble Abeta oligomers or ADDLs bind selectively to neurons at their synaptic loci, and trigger major changes in synapse composition and morphology, which ultimately leads to dendritic spine loss. However, the exact mechanism is not yet fully understood but is suspected to involve some membrane receptor(s).
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228
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Xie Z, Srivastava DP, Photowala H, Kai L, Cahill ME, Woolfrey KM, Shum CY, Surmeier DJ, Penzes P. Kalirin-7 controls activity-dependent structural and functional plasticity of dendritic spines. Neuron 2007; 56:640-56. [PMID: 18031682 PMCID: PMC2118058 DOI: 10.1016/j.neuron.2007.10.005] [Citation(s) in RCA: 301] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2007] [Revised: 06/20/2007] [Accepted: 10/02/2007] [Indexed: 11/29/2022]
Abstract
Activity-dependent rapid structural and functional modifications of central excitatory synapses contribute to synapse maturation, experience-dependent plasticity, and learning and memory and are associated with neurodevelopmental and psychiatric disorders. However, the signal transduction mechanisms that link glutamate receptor activation to intracellular effectors that accomplish structural and functional plasticity are not well understood. Here we report that NMDA receptor activation in pyramidal neurons causes CaMKII-dependent phosphorylation of the guanine-nucleotide exchange factor (GEF) kalirin-7 at residue threonine 95, regulating its GEF activity, leading to activation of small GTPase Rac1 and rapid enlargement of existing spines. Kalirin-7 also interacts with AMPA receptors and controls their synaptic expression. By demonstrating that kalirin expression and spine localization are required for activity-dependent spine enlargement and enhancement of AMPAR-mediated synaptic transmission, our study identifies a signaling pathway that controls structural and functional spine plasticity.
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Affiliation(s)
| | | | - Huzefa Photowala
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Li Kai
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Michael E. Cahill
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Kevin M. Woolfrey
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Cassandra Y. Shum
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - D. James Surmeier
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
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229
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Beg AA, Sommer JE, Martin JH, Scheiffele P. alpha2-Chimaerin is an essential EphA4 effector in the assembly of neuronal locomotor circuits. Neuron 2007; 55:768-78. [PMID: 17785183 DOI: 10.1016/j.neuron.2007.07.036] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 07/23/2007] [Accepted: 07/31/2007] [Indexed: 10/22/2022]
Abstract
The assembly of neuronal networks during development requires tightly controlled cell-cell interactions. Multiple cell surface receptors that control axon guidance and synapse maturation have been identified. However, the signaling mechanisms downstream of these receptors have remained unclear. Receptor signals might be transmitted through dedicated signaling lines defined by specific effector proteins. Alternatively, a single cell surface receptor might couple to multiple effectors with overlapping functions. We identified the neuronal RacGAP alpha2-chimaerin as an effector for the receptor tyrosine kinase EphA4. alpha2-Chimaerin interacts with activated EphA4 and is required for ephrin-induced growth cone collapse in cortical neurons. alpha2-Chimaerin mutant mice exhibit a rabbit-like hopping gait with synchronous hindlimb movements that phenocopies mice lacking EphA4 kinase activity. Anatomical and functional analyses of corticospinal and spinal interneuron projections reveal that loss of alpha2-chimaerin results in impairment of EphA4 signaling in vivo. These findings identify alpha2-chimaerin as an indispensable effector for EphA4 in cortical and spinal motor circuits.
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Affiliation(s)
- Asim A Beg
- Department of Physiology and Cellular Biophysics, Department of Neuroscience, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
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230
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Schrick C, Fischer A, Srivastava DP, Tronson NC, Penzes P, Radulovic J. N-cadherin regulates cytoskeletally associated IQGAP1/ERK signaling and memory formation. Neuron 2007; 55:786-98. [PMID: 17785185 PMCID: PMC2064867 DOI: 10.1016/j.neuron.2007.07.034] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Revised: 06/12/2007] [Accepted: 07/30/2007] [Indexed: 12/20/2022]
Abstract
Cadherin-mediated interactions are integral to synapse formation and potentiation. Here we show that N-cadherin is required for memory formation and regulation of a subset of underlying biochemical processes. N-cadherin antagonistic peptide containing the His-Ala-Val motif (HAV-N) transiently disrupted hippocampal N-cadherin dimerization and impaired the formation of long-term contextual fear memory while sparing short-term memory, retrieval, and extinction. HAV-N impaired the learning-induced phosphorylation of a distinctive, cytoskeletally associated fraction of hippocampal Erk-1/2 and altered the distribution of IQGAP1, a scaffold protein linking cadherin-mediated cell adhesion to the cytoskeleton. This effect was accompanied by reduction of N-cadherin/IQGAP1/Erk-2 interactions. Similarly, in primary neuronal cultures, HAV-N prevented NMDA-induced dendritic Erk-1/2 phosphorylation and caused relocation of IQGAP1 from dendritic spines into the shafts. The data suggest that the newly identified role of hippocampal N-cadherin in memory consolidation may be mediated, at least in part, by cytoskeletal IQGAP1/Erk signaling.
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Affiliation(s)
- Christina Schrick
- Department of Psychiatry and Behavioral Sciences, The Asher Center for Depressive Disorders, Northwestern University, Feinberg School of Medicine, Chicago, USA
| | - Andre Fischer
- Neuropathology Group, European Neuroscience Institute, Goettingen, Germany
| | - Deepak P. Srivastava
- Department of Physiology, Northwestern University, Feinberg School of Medicine, Chicago, USA
| | - Natalie C. Tronson
- Department of Psychiatry and Behavioral Sciences, The Asher Center for Depressive Disorders, Northwestern University, Feinberg School of Medicine, Chicago, USA
| | - Peter Penzes
- Department of Physiology, Northwestern University, Feinberg School of Medicine, Chicago, USA
| | - Jelena Radulovic
- Department of Psychiatry and Behavioral Sciences, The Asher Center for Depressive Disorders, Northwestern University, Feinberg School of Medicine, Chicago, USA
- *Corresponding author: Jelena Radulovic, Department of Psychiatry and Behavioral Sciences, The Asher Center for Depressive Disorders, Northwestern University, Feinberg School of Medicine, 303 East Chicago Avenue, Ward 9-188, Chicago, IL 60611, , Phone: 312 503 4627, Fax: 312 503 0466
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231
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Iwasato T, Katoh H, Nishimaru H, Ishikawa Y, Inoue H, Saito YM, Ando R, Iwama M, Takahashi R, Negishi M, Itohara S. Rac-GAP alpha-chimerin regulates motor-circuit formation as a key mediator of EphrinB3/EphA4 forward signaling. Cell 2007; 130:742-53. [PMID: 17719550 DOI: 10.1016/j.cell.2007.07.022] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Revised: 05/24/2007] [Accepted: 07/16/2007] [Indexed: 11/16/2022]
Abstract
The ephrin/Eph system plays a central role in neuronal circuit formation; however, its downstream effectors are poorly understood. Here we show that alpha-chimerin Rac GTPase-activating protein mediates ephrinB3/EphA4 forward signaling. We discovered a spontaneous mouse mutation, miffy (mfy), which results in a rabbit-like hopping gait, impaired corticospinal axon guidance, and abnormal spinal central pattern generators. Using positional cloning, transgene rescue, and gene targeting, we demonstrated that loss of alpha-chimerin leads to mfy phenotypes similar to those of EphA4(-/-) and ephrinB3(-/-) mice. alpha-chimerin interacts with EphA4 and, in response to ephrinB3/EphA4 signaling, inactivates Rac, which is a positive regulator of process outgrowth. Moreover, downregulation of alpha-chimerin suppresses ephrinB3-induced growth cone collapse in cultured neurons. Our findings indicate that ephrinB3/EphA4 signaling prevents growth cone extension in motor circuit formation via alpha-chimerin-induced inactivation of Rac. They also highlight the role of a Rho family GTPase-activating protein as a key mediator of ephrin/Eph signaling.
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MESH Headings
- Animals
- Animals, Newborn
- Cells, Cultured
- Cerebral Cortex/cytology
- Chimerin 1/metabolism
- Chromosomes, Mammalian
- Crosses, Genetic
- Ephrin-B3/genetics
- Ephrin-B3/metabolism
- Genes, Recessive
- Genetic Linkage
- Mice
- Mice, Inbred C57BL
- Mice, Inbred DBA
- Mice, Knockout
- Mice, Transgenic
- Molecular Sequence Data
- Motor Activity/genetics
- Mutation
- N-Methylaspartate/pharmacology
- Neurons/cytology
- Neurons/metabolism
- Polymorphism, Single Nucleotide
- Serotonin/pharmacology
- Signal Transduction
- Spinal Cord/drug effects
- rac GTP-Binding Proteins/physiology
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Affiliation(s)
- Takuji Iwasato
- Laboratory for Behavioral Genetics, RIKEN Brain Science Institute (BSI), 2-1 Hirosawa Wako-shi, Saitama 351-0198, Japan
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232
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Bourgin C, Murai KK, Richter M, Pasquale EB. The EphA4 receptor regulates dendritic spine remodeling by affecting beta1-integrin signaling pathways. ACTA ACUST UNITED AC 2007; 178:1295-307. [PMID: 17875741 PMCID: PMC2064660 DOI: 10.1083/jcb.200610139] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Remodeling of dendritic spines is believed to modulate the function of excitatory synapses. We previously reported that the EphA4 receptor tyrosine kinase regulates spine morphology in hippocampal pyramidal neurons, but the signaling pathways involved were not characterized (Murai, K.K., L.N. Nguyen, F. Irie, Y. Yamaguchi, and E.B. Pasquale. 2003. Nat. Neurosci. 6:153–160). In this study, we show that EphA4 activation by ephrin-A3 in hippocampal slices inhibits integrin downstream signaling pathways. EphA4 activation decreases tyrosine phosphorylation of the scaffolding protein Crk-associated substrate (Cas) and the tyrosine kinases focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) and also reduces the association of Cas with the Src family kinase Fyn and the adaptor Crk. Consistent with this, EphA4 inhibits β1-integrin activity in neuronal cells. Supporting a functional role for β1 integrin and Cas inactivation downstream of EphA4, the inhibition of integrin or Cas function induces spine morphological changes similar to those associated with EphA4 activation. Furthermore, preventing β1-integrin inactivation blocks the effects of EphA4 on spines. Our results support a model in which EphA4 interferes with integrin signaling pathways that stabilize dendritic spines, thus modulating synaptic interactions with the extracellular environment.
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233
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Shin J, Gu C, Park E, Park S. Identification of phosphotyrosine binding domain-containing proteins as novel downstream targets of the EphA8 signaling function. Mol Cell Biol 2007; 27:8113-26. [PMID: 17875921 PMCID: PMC2169194 DOI: 10.1128/mcb.00794-07] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Eph receptors and ephrins have been implicated in a variety of cellular processes, including morphology and motility, because of their ability to modulate intricate signaling networks. Here we show that the phosphotyrosine binding (PTB) domain-containing proteins AIDA-1b and Odin are tightly associated with the EphA8 receptor in response to ligand stimulation. Both AIDA-1b and Odin belong to the ankyrin repeat and sterile alpha motif domain-containing (Anks) protein family. The PTB domain of Anks family proteins is crucial for their association with the juxtamembrane domain of EphA8, whereas EphA8 tyrosine kinase activity is not required for this protein-protein interaction. In addition, we found that Odin is a more physiologically relevant partner of EphA8 in mammalian cells. Interestingly, overexpression of the Odin PTB domain alone attenuated EphA8-mediated inhibition of cell migration in HEK293 cells, suggesting that it acts as a dominant-negative mutant of the endogenous Odin protein. More importantly, small interfering RNA-mediated Odin silencing significantly diminished ephrinA5-induced EphA8 signaling effects, which inhibit cell migration in HEK293 cells and retract growing neurites of Neuro2a cells. Taken together, our findings support a possible function for Anks family proteins as scaffolding proteins of the EphA8 signaling pathway.
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Affiliation(s)
- Jongdae Shin
- Department of Biological Science, Sookmyung Women's University, Chungpa-Dong 2-Ka, Yongsan-Ku, Seoul 140-742, South Korea
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234
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Jacobs T, Causeret F, Nishimura YV, Terao M, Norman A, Hoshino M, Nikolić M. Localized activation of p21-activated kinase controls neuronal polarity and morphology. J Neurosci 2007; 27:8604-15. [PMID: 17687038 PMCID: PMC2080820 DOI: 10.1523/jneurosci.0765-07.2007] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In the developing forebrain, neuronal polarization is a stepwise and initially reversible process that underlies correct migration and axon specification. Many aspects of cytoskeletal changes that accompany polarization are currently molecularly undefined and thus poorly understood. Here we reveal that the p21-activated kinase (Pak1) is essential for the specification of an axon and dendrites. In hippocampal neurons, activation of Pak1 is spatially restricted to the immature axon despite its uniform presence in all neurites. Hyperactivation of Pak1 at the membrane of all neurites or loss of Pak1 expression disrupts both neuronal morphology and the distinction between an axon and dendrites. We reveal that Pak1 acts on polarity in a kinase-dependent manner, by affecting the F-actin and microtubule cytoskeleton at least in part through Rac1 and cofilin. Our data are the first to demonstrate the importance of localized Pak1 kinase activation for neuronal polarization and differentiation.
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Affiliation(s)
- Tom Jacobs
- Department of Cellular and Molecular Neuroscience, Division of Neuroscience and Mental Health, Imperial College School of Medicine, Charing Cross Campus, London W6 8RP, United Kingdom, and
| | - Frédéric Causeret
- Department of Cellular and Molecular Neuroscience, Division of Neuroscience and Mental Health, Imperial College School of Medicine, Charing Cross Campus, London W6 8RP, United Kingdom, and
| | - Yoshiaki V. Nishimura
- Department of Pathology and Tumor Biology, Kyoto University Graduate School of Medicine, Sakyo-ku, Kyoto 606-8501, Japan
| | - Mami Terao
- Department of Pathology and Tumor Biology, Kyoto University Graduate School of Medicine, Sakyo-ku, Kyoto 606-8501, Japan
| | - Adele Norman
- Department of Cellular and Molecular Neuroscience, Division of Neuroscience and Mental Health, Imperial College School of Medicine, Charing Cross Campus, London W6 8RP, United Kingdom, and
| | - Mikio Hoshino
- Department of Pathology and Tumor Biology, Kyoto University Graduate School of Medicine, Sakyo-ku, Kyoto 606-8501, Japan
| | - Margareta Nikolić
- Department of Cellular and Molecular Neuroscience, Division of Neuroscience and Mental Health, Imperial College School of Medicine, Charing Cross Campus, London W6 8RP, United Kingdom, and
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235
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Zhang Y, Sawada T, Jing X, Yokote H, Yan X, Sakaguchi K. Regulation of ephexin1, a guanine nucleotide exchange factor of Rho family GTPases, by fibroblast growth factor receptor-mediated tyrosine phosphorylation. J Biol Chem 2007; 282:31103-12. [PMID: 17702745 DOI: 10.1074/jbc.m704430200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fibroblast growth factor (FGF) signal is implicated in not only cell proliferation, but cell migration and morphological changes. Several different Rho family GTPases downstream of the Ras/ERK pathway are postulated to mediate the latter functions. However, none have been recognized to be directly coupled to FGF receptors (FGFRs). We have previously reported that EphA4 and FGFRs hetero-oligomerize through their cytoplasmic domains, trans-activate each other, and transduce a signal for cell proliferation through a docking protein, FRS2alpha (Yokote, H., Fujita, K., Jing, X., Sawada, T., Liang, S., Yao, L., Yan, X., Zhang, Y., Schlessinger, J., and Sakaguchi, K. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 18866-18871). Here, we have found that ephexin1, a guanine nucleotide exchange factor for Rho family GTPases, constitutes another downstream component of the receptor complex. Ephexin1 directly binds to the kinase domain of FGFR mainly through its DH and PH domains. The binding appears to become weaker and limited to the DH domain when FGFRs become activated. FGFR-mediated phosphorylation of ephexin1 enhances the guanine nucleotide exchange activity toward RhoA without affecting the activity to Rac1 or Cdc42. The FGFR-mediated tyrosine phosphorylation includes, but is not limited to, the residue (Tyr-87) phosphorylated by Src family kinase, which is known to be activated following EphA4 activation. The Tyr-to-Asp mutations that mimic the tyrosine phosphorylation in some of the putative FGFR-mediated phosphorylation sites increase the nucleotide exchange activity for RhoA without changing the activity for Rac1 or Cdc42. From these results, we conclude that ephexin1 is located immediately downstream of the EphA4-FGFR complex and the function is altered by the FGFR-mediated tyrosine phosphorylation at multiple sites.
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Affiliation(s)
- Yueqiang Zhang
- Department of Molecular Cell Biology, Institute of Advanced Medicine, Wakayama Medical University, 811-1 Kimiidera, Wakayama 641-8509, Japan
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236
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Aoto J, Ting P, Maghsoodi B, Xu N, Henkemeyer M, Chen L. Postsynaptic ephrinB3 promotes shaft glutamatergic synapse formation. J Neurosci 2007; 27:7508-19. [PMID: 17626212 PMCID: PMC6672605 DOI: 10.1523/jneurosci.0705-07.2007] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Excitatory synapses in the CNS are formed on both dendritic spines and shafts. Recent studies show that the density of shaft synapses may be independently regulated by behavioral learning and the induction of synaptic plasticity, suggesting that distinct mechanisms are involved in regulating these two types of synapses. Although the molecular mechanisms underlying spinogenesis and spine synapse formation are being delineated, those regulating shaft synapses are still unknown. Here, we show that postsynaptic ephrinB3 expression promotes the formation of glutamatergic synapses specifically on the shafts, not on spines. Reducing or increasing postsynaptic ephrinB3 expression selectively decreases or increases shaft synapse density, respectively. In the ephrinB3 knock-out mouse, although spine synapses are normal, shaft synapse formation is reduced in the hippocampus. Overexpression of glutamate receptor-interacting protein 1 (GRIP1) rescues ephrinB3 knockdown phenotype by restoring shaft synapse density. GRIP1 knockdown prevents the increase in shaft synapse density induced by ephrinB3 overexpression. Together, our results reveal a novel mechanism for independent modulation of shaft synapses through ephrinB3 reverse signaling.
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Affiliation(s)
- Jason Aoto
- Department of Molecular and Cell Biology and
| | - Pamela Ting
- Department of Molecular and Cell Biology and
| | | | - Nanjie Xu
- Department of Developmental Biology and Kent Waldrep Center for Basic Research on Nerve Growth and Regeneration, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Mark Henkemeyer
- Department of Developmental Biology and Kent Waldrep Center for Basic Research on Nerve Growth and Regeneration, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Lu Chen
- Department of Molecular and Cell Biology and
- Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720-3200, and
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237
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Zhou L, Martinez SJ, Haber M, Jones EV, Bouvier D, Doucet G, Corera AT, Fon EA, Zisch AH, Murai KK. EphA4 signaling regulates phospholipase Cgamma1 activation, cofilin membrane association, and dendritic spine morphology. J Neurosci 2007; 27:5127-38. [PMID: 17494698 PMCID: PMC6672384 DOI: 10.1523/jneurosci.1170-07.2007] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Specialized postsynaptic structures known as dendritic spines are the primary sites of glutamatergic innervation at synapses of the CNS. Previous studies have shown that spines rapidly remodel their actin cytoskeleton to modify their shape and this has been associated with changes in synaptic physiology. However, the receptors and signaling intermediates that restructure the actin network in spines are only beginning to be identified. We reported previously that the EphA4 receptor tyrosine kinase regulates spine morphology. However, the signaling pathways downstream of EphA4 that induce spine retraction on ephrin ligand binding remain poorly understood. Here, we demonstrate that ephrin stimulation of EphA4 leads to the recruitment and activation of phospholipase Cgamma1 (PLCgamma1) in heterologous cells and in hippocampal slices. This interaction occurs through an Src homology 2 domain of PLCgamma1 and requires the EphA4 juxtamembrane tyrosines. In the brain, PLCgamma1 is found in multiple compartments of synaptosomes and is readily found in postsynaptic density fractions. Consistent with this, PLC activity is required for the maintenance of spine morphology and ephrin-induced spine retraction. Remarkably, EphA4 and PLC activity modulate the association of the actin depolymerizing/severing factor cofilin with the plasma membrane. Because cofilin has been implicated previously in the structural plasticity of spines, this signaling may enable cofilin to depolymerize actin filaments and restructure spines at sites of ephrin-EphA4 contact.
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Affiliation(s)
- Lei Zhou
- Center for Research in Neuroscience, Department of Neurology and Neurosurgery, The Research Institute of the McGill University Health Center, Montreal General Hospital, Montreal, Quebec, Canada H3G 1A4
| | - Sarah J. Martinez
- Center for Research in Neuroscience, Department of Neurology and Neurosurgery, The Research Institute of the McGill University Health Center, Montreal General Hospital, Montreal, Quebec, Canada H3G 1A4
| | - Michael Haber
- Center for Research in Neuroscience, Department of Neurology and Neurosurgery, The Research Institute of the McGill University Health Center, Montreal General Hospital, Montreal, Quebec, Canada H3G 1A4
| | - Emma V. Jones
- Center for Research in Neuroscience, Department of Neurology and Neurosurgery, The Research Institute of the McGill University Health Center, Montreal General Hospital, Montreal, Quebec, Canada H3G 1A4
| | - David Bouvier
- Département de Pathologie et Biologie Cellulaire and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada H3C 3J7
| | - Guy Doucet
- Département de Pathologie et Biologie Cellulaire and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada H3C 3J7
| | - Amadou T. Corera
- Center for Neuronal Survival and Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 3B4
| | - Edward A. Fon
- Center for Neuronal Survival and Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 3B4
| | - Andreas H. Zisch
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland, and
- Center for Integrative Human Physiology, University of Zurich, 8091 Zurich, Switzerland
| | - Keith K. Murai
- Center for Research in Neuroscience, Department of Neurology and Neurosurgery, The Research Institute of the McGill University Health Center, Montreal General Hospital, Montreal, Quebec, Canada H3G 1A4
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238
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Chen LY, Rex CS, Casale MS, Gall CM, Lynch G. Changes in synaptic morphology accompany actin signaling during LTP. J Neurosci 2007; 27:5363-72. [PMID: 17507558 PMCID: PMC6672340 DOI: 10.1523/jneurosci.0164-07.2007] [Citation(s) in RCA: 221] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Stabilization of long-term potentiation (LTP) is commonly proposed to involve changes in synaptic morphology and reorganization of the spine cytoskeleton. Here we tested whether, as predicted from this hypothesis, induction of LTP by theta-burst stimulation activates an actin regulatory pathway and alters synapse morphology within the same dendritic spines. TBS increased severalfold the numbers of spines containing phosphorylated (p) p21-activated kinase (PAK) or its downstream target cofilin; the latter regulates actin filament assembly. The PAK/cofilin phosphoproteins were increased at 2 min but not 30 s post-TBS, peaked at 7 min, and then declined. Double immunostaining for the postsynaptic density protein PSD95 revealed that spines with high pPAK or pCofilin levels had larger synapses (+60-70%) with a more normal size frequency distribution than did neighboring spines. Based on these results and simulations of shape changes to synapse-like objects, we propose that theta stimulation markedly increases the probability that a spine will enter a state characterized by a large, ovoid synapse and that this morphology is important for expression and later stabilization of LTP.
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Affiliation(s)
| | - Christopher S. Rex
- Department of Neurobiology and Behavior, University of California, Irvine, California 92697-4550
| | - Malcolm S. Casale
- Psychiatry and Human Behavior, University of California, Irvine, California 92697-4292, and
| | - Christine M. Gall
- Departments of Anatomy and Neurobiology and
- Department of Neurobiology and Behavior, University of California, Irvine, California 92697-4550
| | - Gary Lynch
- Psychiatry and Human Behavior, University of California, Irvine, California 92697-4292, and
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239
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Cesa R, Scelfo B, Strata P. Activity-dependent presynaptic and postsynaptic structural plasticity in the mature cerebellum. J Neurosci 2007; 27:4603-11. [PMID: 17460073 PMCID: PMC6673001 DOI: 10.1523/jneurosci.5617-06.2007] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Two models of spine formation have been proposed. Spines can derive from emerging dendritic filopodia that have encountered presynaptic partners, or presynaptic molecules may induce the spine maturation event directly from the dendritic shaft. The first model applies better to the Purkinje cell (PC), because numerous free spines have been described in several conditions, particularly when granule cells degenerate before parallel fiber (PF) synapses are formed. A large number of new spines, many of them being free, appear in the proximal dendritic domain after blockage of electrical activity by tetrodotoxin (TTX). A complete blockage of the AMPA receptors by NBQX (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzoquinoxaline-7-sulfonamide), leading to a complete absence of PF- and climbing fiber (CF)-evoked EPSCs and of spontaneous glutamatergic quantal events, mimics the TTX effect. In contrast, metabotropic glutamate receptor blockage by MCPG [(S)-alpha-methyl-4-carboxyphenylglycine] is ineffective. In normal conditions, in the proximal dendritic domain of the PC, clusters of a few spines are present only under each CF varicosity. It has been proposed that the active CF is responsible for spine pruning in the territory surrounding the CF synapses. Here, we show that such a pruning is mediated by AMPA but not by metabotropic receptors. Finally, after AMPA receptor blockage, there is a reduced number of spines in each spine cluster underlying CF varicosity. In conclusion, PCs tend to express spines over the entire dendritic territory. CF activity reinforces the CF synaptic contacts and actively suppresses spines in the surrounding territory, which is an effect mediated by AMPA receptors.
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Affiliation(s)
- Roberta Cesa
- Department of Neuroscience, University of Turin, 10125 Torino, Italy.
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240
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Parri M, Buricchi F, Giannoni E, Grimaldi G, Mello T, Raugei G, Ramponi G, Chiarugi P. EphrinA1 activates a Src/focal adhesion kinase-mediated motility response leading to rho-dependent actino/myosin contractility. J Biol Chem 2007; 282:19619-28. [PMID: 17449913 DOI: 10.1074/jbc.m701319200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eph receptors and ephrin ligands are widely expressed in epithelial cells and mediate cell repulsive motility through heterotypic cell-cell interactions. Several Ephs, including EphA2, are greatly overexpressed in certain tumors, in correlation with poor prognosis and high vascularity in cancer tissues. The ability of several Eph receptors to regulate cell migration and invasion likely contribute to tumor progression and metastasis. We report here that in prostatic carcinoma cells ephrinA1 elicits a repulsive response that is executed through a Rho-dependent actino/myosin contractility activation, ultimately leading to retraction of the cell body. This appears to occur through assembly of an EphA2-associated complex involving the two kinases Src and focal adhesion kinase (FAK). EphrinA1-mediated repulsion leads to the selective phosphorylation of Tyr-576/577 of FAK, enhancing FAK kinase activity. The repulsive response elicited by ephrinA1 in prostatic carcinoma cells is mainly driven by a Rho-mediated phosphorylation of myosin light chain II, in which Src and FAK activation are required steps. Consequently, Src and FAK are upstream regulators of the overall response induced by ephrinA1/EphA2, instructing cells to retract the cell body and to move away, probably facilitating dissemination and tissue invasion of ephrin-sensitive carcinomas.
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Affiliation(s)
- Matteo Parri
- Department of Biochemical Sciences, University of Florence, Viale Morgagni 50, 50134 Florence, Italy
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241
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Fu AKY, Ip NY. Cyclin-dependent kinase 5 links extracellular cues to actin cytoskeleton during dendritic spine development. Cell Adh Migr 2007; 1:110-2. [PMID: 19270534 DOI: 10.4161/cam.1.2.4617] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Emerging evidence has indicated a regulatory role of cyclin-dependent kinase 5 (Cdk5) in synaptic plasticity as well as in higher brain functions, such as learning and memory. However, the molecular and cellular mechanisms underlying the actions of Cdk5 at synapses remain unclear. Recent findings demonstrate that Cdk5 regulates dendritic spine morphogenesis through modulating actin dynamics. Ephexin1 and WAVE-1, two important regulators of the actin cytoskeleton, have both been recently identified as substrates for Cdk5. Importantly, phosphorylation of these proteins by Cdk5 leads to dendritic spine loss, revealing a potential mechanism by which Cdk5 regulates synapse remodeling. Furthermore, Cdk5-dependent phosphorylation of ephexin1 is required for the ephrin-A1 mediated spine retraction, pointing to a critical role of Cdk5 in conveying signals from extracellular cues to actin cytoskeleton at synapses. Taken together, understanding the precise regulation of Cdk5 and its downstream targets at synapses would provide important insights into the multi-regulatory roles of Cdk5 in actin remodeling during dendritic spine development.
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Affiliation(s)
- Amy K Y Fu
- Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Hong Kong, China
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242
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Tolias KF, Bikoff JB, Kane CG, Tolias CS, Hu L, Greenberg ME. The Rac1 guanine nucleotide exchange factor Tiam1 mediates EphB receptor-dependent dendritic spine development. Proc Natl Acad Sci U S A 2007; 104:7265-70. [PMID: 17440041 PMCID: PMC1855368 DOI: 10.1073/pnas.0702044104] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Dendritic spines are small, actin-rich protrusions on the surface of dendrites that receive the majority of excitatory synaptic inputs in the brain. The formation and remodeling of spines, processes that underlie synaptic development and plasticity, are regulated in part by Eph receptor tyrosine kinases. However, the mechanism by which Ephs regulate actin cytoskeletal remodeling necessary for spine development is not fully understood. Here, we report that the Rac1 guanine nucleotide exchange factor Tiam1 interacts with the EphB2 receptor in a kinase-dependent manner. Activation of EphBs by their ephrinB ligands induces the tyrosine phosphorylation and recruitment of Tiam1 to EphB complexes containing NMDA-type glutamate receptors. Either knockdown of Tiam1 protein by RNAi or inhibition of Tiam1 function with a dominant-negative Tiam1 mutant blocks dendritic spine formation induced by ephrinB1 stimulation. Taken together, these findings suggest that EphBs regulate spine development in part by recruiting, phosphorylating, and activating Tiam1. Tiam1 can then promote Rac1-dependent actin cytoskeletal remodeling required for dendritic spine morphogenesis.
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Affiliation(s)
- Kimberley F. Tolias
- *Neurobiology Program, Children's Hospital, and
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115
| | - Jay B. Bikoff
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115
| | | | | | - Linda Hu
- *Neurobiology Program, Children's Hospital, and
| | - Michael E. Greenberg
- *Neurobiology Program, Children's Hospital, and
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115
- To whom correspondence should be addressed. E-mail:
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243
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Bisson N, Poitras L, Mikryukov A, Tremblay M, Moss T. EphA4 signaling regulates blastomere adhesion in the Xenopus embryo by recruiting Pak1 to suppress Cdc42 function. Mol Biol Cell 2007; 18:1030-43. [PMID: 17215521 PMCID: PMC1805096 DOI: 10.1091/mbc.e06-04-0294] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2006] [Revised: 12/04/2006] [Accepted: 12/29/2006] [Indexed: 12/19/2022] Open
Abstract
The control of cell adhesion is an important mechanism by which Eph receptors regulate cell sorting during development. Activation of EphA4 in Xenopus blastulae induces a reversible, cell autonomous loss-of-adhesion and disruption of the blastocoel roof. We show this phenotype is rescued by Nckbeta (Grb4) dependent on its interaction with EphA4. Xenopus p21(Cdc42/Rac)-activated kinase xPAK1 interacts with Nck, is activated in embryo by EphA4 in an Nck-dependent manner, and is required for EphA4-induced loss-of-adhesion. Ectopic expression of xPAK1 phenocopies EphA4 activation. This does not require the catalytic activity of xPAK1, but it does require its GTPase binding domain and is enhanced by membrane targeting. Indeed, membrane targeting of the GTPase binding domain (GBD) of xPAK1 alone is sufficient to phenocopy EphA4 loss-of-adhesion. Both EphA4 and the xPAK1-GBD down-regulate RhoA-GTP levels, and consistent with this, loss-of-adhesion can be rescued by activated Cdc42, Rac, and RhoA and can be epistatically induced by dominant-negative RhoA. Despite this, neither Cdc42 nor Rac activities are down-regulated by EphA4 activation or by the xPAK1-GBD. Together, the data suggest that EphA4 activation sequesters active Cdc42 and in this way down-regulates cell-cell adhesion. This novel signaling pathway suggests a mechanism for EphA4-guided migration.
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Affiliation(s)
- Nicolas Bisson
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, Québec, G1R 2J6 Québec, Canada
| | - Luc Poitras
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, Québec, G1R 2J6 Québec, Canada
| | - Alexander Mikryukov
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, Québec, G1R 2J6 Québec, Canada
| | - Michel Tremblay
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, Québec, G1R 2J6 Québec, Canada
| | - Tom Moss
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, Québec, G1R 2J6 Québec, Canada
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244
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Segura I, Essmann CL, Weinges S, Acker-Palmer A. Grb4 and GIT1 transduce ephrinB reverse signals modulating spine morphogenesis and synapse formation. Nat Neurosci 2007; 10:301-10. [PMID: 17310244 DOI: 10.1038/nn1858] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2006] [Accepted: 01/25/2007] [Indexed: 02/08/2023]
Abstract
Dendritic spines are small protrusions emerging from dendrites that receive excitatory input. The process of spine morphogenesis occurs both in the developing brain and during synaptic plasticity. Molecules regulating the cytoskeleton are involved in spine formation and maintenance. Here we show that reverse signaling by the transmembrane ligands for Eph receptors, ephrinBs, is required for correct spine morphogenesis. The molecular mechanism underlying this function of ephrinBs involves the SH2 and SH3 domain-containing adaptor protein Grb4 and the G protein-coupled receptor kinase-interacting protein (GIT) 1. Grb4 binds by its SH2 domain to Tyr392 in the synaptic localization domain of GIT1. Phosphorylation of Tyr392 and the recruitment of GIT1 to synapses are regulated by ephrinB activation. Disruption of this pathway in cultured rat hippocampal neurons impairs spine morphogenesis and synapse formation. We thus show an important role for ephrinB reverse signaling in spine formation and have mapped the downstream pathway involved in this process.
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Affiliation(s)
- Inmaculada Segura
- Max-Planck Institute of Neurobiology, Am Klopferspitz 18, D-82152 Martinsried, Germany
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245
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Dalva MB, McClelland AC, Kayser MS. Cell adhesion molecules: signalling functions at the synapse. Nat Rev Neurosci 2007; 8:206-20. [PMID: 17299456 PMCID: PMC4756920 DOI: 10.1038/nrn2075] [Citation(s) in RCA: 423] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Many cell adhesion molecules are localized at synaptic sites in neuronal axons and dendrites. These molecules bridge pre- and postsynaptic specializations but do far more than simply provide a mechanical link between cells. In this review, we will discuss the roles these proteins have during development and at mature synapses. Synaptic adhesion proteins participate in the formation, maturation, function and plasticity of synaptic connections. Together with conventional synaptic transmission mechanisms, these molecules are an important element in the trans-cellular communication mediated by synapses.
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Affiliation(s)
- Matthew B Dalva
- University of Pennsylvania Medical Center, Department of Neuroscience, BRB II/III, Room 1114, 421 Curie Blvd., Philadelphia, Pennsylvania 19104, USA.
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246
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Schubert V, Dotti CG. Transmitting on actin: synaptic control of dendritic architecture. J Cell Sci 2007; 120:205-12. [PMID: 17215449 DOI: 10.1242/jcs.03337] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Excitatory synaptic transmission in the central nervous system mainly takes place at dendritic spines, highly motile protrusions on the dendritic surface. Depending on the stimuli received, dendritic spines undergo rapid actin-based changes in their morphology. This plasticity appears to involve signaling through numerous proteins that control the organization of the actin cytoskeleton (actin regulators). At least in part, recruitment and activation of these depends on neurotransmitter receptors at the post-synapse, which directly link neurotransmission to changes in dendritic spine architecture. However, other, non-neurotransmitter-receptors present at dendritic spines also participate. It is likely that several receptor types can control the activity of a single actin-regulatory pathway and it is the complex integration of numerous signals that determines the overall architecture of a dendritic spine.
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Affiliation(s)
- Vanessa Schubert
- Cavalieri Ottolenghi Scientific Institute, Universita degli Studi di Torino, A.O. San Luigi Gonzaga, Regione Gonzole 10, 10043 Orbassano (Torino), Italy.
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247
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Hayashi K, Ohshima T, Hashimoto M, Mikoshiba K. Pak1 regulates dendritic branching and spine formation. Dev Neurobiol 2007; 67:655-69. [PMID: 17443815 DOI: 10.1002/dneu.20363] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The serine/threonine kinase p21-activated kinase 1 (Pak1) modulates actin and microtubule dynamics. The neuronal functions of Pak1, despite its abundant expression in the brain, have not yet been fully delineated. Previously, we reported that Pak1 mediates initiation of dendrite formation. In the present study, the role of Pak1 in dendritogenesis, spine formation and maintenance was examined in detail. Overexpression of constitutively active-Pak1 in immature cortical neurons increased not only the number of the primary branching on apical dendrites but also the number of basal dendrites. In contrast, introduction of dominant negative-Pak caused a reduction in both of these morphological features. The length and the number of secondary apical branch points of dendrites were not significantly different in cultured neurons expressing these mutant forms, suggesting that Pak1 plays a role in dendritogenesis. Pak1 also plays a role in the formation and maintenance of spines, as evidenced by the altered spine morphology, resulting from overexpression of mutant forms of Pak1 in immature and mature hippocampal neurons. Thus, our results provide further evidence of the key role of Pak1 in the regulation of dendritogenesis, dendritic arborization, the spine formation, and maintenance.
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Affiliation(s)
- Kanehiro Hayashi
- Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN, Wako-shi, Saitama 351-0198, Japan
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248
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de Wit J, Verhaagen J. Proteoglycans as modulators of axon guidance cue function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 600:73-89. [PMID: 17607948 DOI: 10.1007/978-0-387-70956-7_7] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Organizing a functional neuronal network requires the precise wiring of neuronal connections. In order to find their correct targets, growth cones navigate through the extracellular matrix guided by secreted and membrane-bound molecules of the slit, netrin, ephrin and semaphorin families. Although many of these axon guidance molecules are able to bind to heparan sulfate proteoglycans, the role of proteoglycans in regulating axon guidance cue function is only now beginning to be understood. Recent developmental studies in a wide range of model organisms have revealed a crucial role for heparan sulfate proteoglycans as modulators of key signaling pathways in axon guidance. In addition, emerging evidence indicates an essential role for chondroitin sulfate proteoglycans in modifying the guidance function of semaphorins. It is becoming increasingly clear that extracellular matrix molecules, rather than just constituting a structural scaffold, can critically influence axon guidance cue function in development, and may continue to do so in the injured adult nervous system.
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Affiliation(s)
- Joris de Wit
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands.
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249
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Evans IR, Renne T, Gertler FB, Nobes CD. Ena/VASP proteins mediate repulsion from ephrin ligands. J Cell Sci 2006; 120:289-98. [PMID: 17179204 DOI: 10.1242/jcs.03333] [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] [Indexed: 01/18/2023] Open
Abstract
Ena/VASP proteins negatively regulate cell motility and contribute to repulsion from several guidance cues; however, there is currently no evidence for a role downstream of Eph receptors. Eph receptors mediate repulsion from ephrins at sites of intercellular contact during several developmental migrations. For example, the expression of ephrin-Bs in posterior halves of somites restricts neural crest cell migration to the anterior halves. Here we show that ephrin-B2 destabilises neural crest cell lamellipodia when presented in a substrate-bound or soluble form. Our timelapse studies show that repulsive events are associated with the rearward collapse and subsequent loss of lamellipodia as membrane ruffles. We hypothesise that Ena/VASP proteins contribute to repulsion from ephrins by destabilising cellular protrusions and show that Ena/VASP-deficient fibroblasts exhibit reduced repulsion from both ephrin-A and ephrin-B stripes compared to wild-type controls. Moreover, when EphB4 and ephrin-B2 were expressed in neighbouring Swiss 3T3 fibroblasts, VASP and Mena co-accumulated with activated Eph receptors at protrusions formed by EphB4-expressing cells. Sequestration of Ena/VASP proteins away from the periphery of these cells inhibited Eph receptor internalisation, a process that facilitates repulsion. Our results suggest that Ena/VASP proteins regulate ephrin-induced Eph receptor signalling events, possibly by destabilising lamellipodial protrusions.
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Affiliation(s)
- Iwan R Evans
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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250
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Kayser MS, McClelland AC, Hughes EG, Dalva MB. Intracellular and trans-synaptic regulation of glutamatergic synaptogenesis by EphB receptors. J Neurosci 2006; 26:12152-64. [PMID: 17122040 PMCID: PMC6675446 DOI: 10.1523/jneurosci.3072-06.2006] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The majority of mature excitatory synapses in the CNS are found on dendritic spines and contain AMPA- and NMDA-type glutamate receptors apposed to presynaptic specializations. EphB receptor tyrosine kinase signaling has been implicated in both NMDA-type glutamate receptor clustering and dendritic spine formation, but it remains unclear whether EphB plays a broader role in presynaptic and postsynaptic development. Here, we find that EphB2 is involved in organizing excitatory synapses through the independent activities of particular EphB2 protein domains. We demonstrate that EphB2 controls AMPA-type glutamate receptor localization through PDZ (postsynaptic density-95/Discs large/zona occludens-1) binding domain interactions and triggers presynaptic differentiation via its ephrin binding domain. Knockdown of EphB2 in dissociated neurons results in decreased functional synaptic inputs, spines, and presynaptic specializations. Mice lacking EphB1-EphB3 have reduced numbers of synapses, and defects are rescued with postnatal reexpression of EphB2 in single neurons in brain slice. These results demonstrate that EphB2 acts to control the organization of specific classes of mature glutamatergic synapses.
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Affiliation(s)
- Matthew S. Kayser
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
| | - Andrew C. McClelland
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
| | - Ethan G. Hughes
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
| | - Matthew B. Dalva
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
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