251
|
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.
Collapse
Affiliation(s)
- Joris de Wit
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands.
| | | |
Collapse
|
252
|
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.
Collapse
Affiliation(s)
- Iwan R Evans
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
| | | | | | | |
Collapse
|
253
|
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.
Collapse
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
| |
Collapse
|
254
|
Aoto J, Chen L. Bidirectional ephrin/Eph signaling in synaptic functions. Brain Res 2006; 1184:72-80. [PMID: 17166489 PMCID: PMC2170431 DOI: 10.1016/j.brainres.2006.11.033] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Revised: 11/12/2006] [Accepted: 11/14/2006] [Indexed: 12/25/2022]
Abstract
Eph receptors, the largest family of receptor tyrosine kinases, and their membrane bound ligands, the ephrins, are involved in multiple developmental and adult processes within and outside of the nervous system. Bi-directional signaling from both the receptor and the ligand is initiated by ephrin-Eph binding upon cell-cell contact, and involves interactions with distinct subsets of downstream signaling molecules related to specific functions. In the CNS, Ephs and ephrins act as attractive/repulsive, migratory and cell adhesive cues during development and participate in synaptic functions in adult animals. In this review, we will focus on recent findings highlighting the functions of ephrin/Eph signaling in dendritic spine morphogenesis, synapse formation and synaptic plasticity.
Collapse
Affiliation(s)
- Jason Aoto
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200
| | - Lu Chen
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200
- Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720-3200
- * Address Correspondence to: Lu Chen, Department of Molecular and Cell Biology, University of California, 201 LSA, MC 3200, Berkeley, CA 94720-3200, Phone: (510) 643-8163, Fax: (510) 643-6791,
| |
Collapse
|
255
|
Fu WY, Chen Y, Sahin M, Zhao XS, Shi L, Bikoff JB, Lai KO, Yung WH, Fu AKY, Greenberg ME, Ip NY. Cdk5 regulates EphA4-mediated dendritic spine retraction through an ephexin1-dependent mechanism. Nat Neurosci 2006; 10:67-76. [PMID: 17143272 DOI: 10.1038/nn1811] [Citation(s) in RCA: 259] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2006] [Accepted: 11/06/2006] [Indexed: 11/08/2022]
Abstract
The development of dendritic spines is thought to be crucial for synaptic plasticity. Dendritic spines are retracted upon Eph receptor A4 (EphA4) activation, but the mechanisms that control this process are not well understood. Here we report an important function of cyclin-dependent kinase 5 (Cdk5) in EphA4-dependent spine retraction in mice. We found that blocking Cdk5 activity inhibits ephrin-A1-triggered spine retraction and reduction of mEPSC frequency at hippocampal synapses. The activation of EphA4 resulted in the recruitment of Cdk5 to EphA4, leading to the tyrosine phosphorylation and activation of Cdk5. EphA4 and Cdk5 then enhanced the activation of ephexin1, a guanine-nucleotide exchange factor that regulates activation of the small Rho GTPase RhoA. The association between EphA4 and ephexin1 was significantly reduced in Cdk5(-/-) brains and Cdk5-dependent phosphorylation of ephexin1 was required for the ephrin-A1-mediated regulation of spine density. These findings suggest that ephrin-A1 promotes EphA4-dependent spine retraction through the activation of Cdk5 and ephexin1, which in turn modulates actin cytoskeletal dynamics.
Collapse
Affiliation(s)
- Wing-Yu Fu
- Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
256
|
Nodé-Langlois R, Muller D, Boda B. Sequential implication of the mental retardation proteins ARHGEF6 and PAK3 in spine morphogenesis. J Cell Sci 2006; 119:4986-93. [PMID: 17105769 DOI: 10.1242/jcs.03273] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The biological mechanisms underlying the mental retardation associated with mutation of the ARHGEF6 gene, a Rac1/Cdc42 exchange factor, are still unknown, although defects in the plasticity of synaptic networks have been postulated. We have cloned the rat ARHGEF6 gene and investigated, using a transfection approach, its involvement in spine morphogenesis and its relationship to p21-activated kinase 3 (PAK3). We found that expression of tagged ARHGEF6 in hippocampal slice cultures shows a punctate staining in dendritic spines that colocalizes with PSD95. Over-expression of ARHGEF6, of PAK3 or constitutively active PAK3 did not alter spine morphology. By contrast, knockdown of ARHGEF6 using a siRNA approach resulted in abnormalities in spine morphology similar to those reported with knockdown of PAK3. This phenotype could be rescued through co-expression of a constitutively active PAK3 protein, but not with wild-type PAK3. Together, these results indicate that ARHGEF6 is localized in dendritic spines where it contributes to regulate spine morphogenesis probably by acting through a downstream activation of PAK3. Similar mechanisms are thus likely to underlie the mental retardation induced by mutations of ARHGEF6 and PAK3.
Collapse
Affiliation(s)
- Roxanne Nodé-Langlois
- Department of Basic Neuroscience, University of Geneva, School of Medicine, 1211 Geneva 4, Switzerland
| | | | | |
Collapse
|
257
|
Kim E, Ko J. Molecular organization and assembly of the postsynaptic density of excitatory brain synapses. Results Probl Cell Differ 2006; 43:1-23. [PMID: 17068965 DOI: 10.1007/400_011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Abstract
The postsynaptic density (PSD) is a postsynaptic membrane specialization at excitatory synapses. The PSD is made of macromolecular multiprotein complexes, which contain a variety of synaptic proteins including membrane, scaffolding, and signaling proteins. By coaggregating with postsynaptic cell adhesion molecules, PSD proteins promote the formation and maturation of excitatory synapses. PSD proteins organize signaling pathways to coordinate structural and functional changes in synapses, and they regulate trafficking and recycling of glutamate receptors, which determines synaptic strength and plasticity. Synaptic activity dynamically regulates the assembly of the PSD through mechanisms including protein phosphorylation, palmitoylation, and protein degradation. PSD proteins associate with diverse motor proteins, suggesting that they function as adaptors linking motors to their specific cargoes.
Collapse
Affiliation(s)
- Eunjoon Kim
- National Creative Research Initiative Center for Synaptogenesis and Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon.
| | | |
Collapse
|
258
|
Catching a GEF by its tail. Trends Cell Biol 2006; 17:36-43. [PMID: 17126549 DOI: 10.1016/j.tcb.2006.11.004] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2006] [Revised: 10/19/2006] [Accepted: 11/15/2006] [Indexed: 12/30/2022]
Abstract
The activation of Rho GTPases is mediated by guanine-nucleotide exchange factors (GEFs), which catalyze the exchange of GDP for GTP. Rho-GEFs are a very diverse family, with >70 members in humans. Bioinformatics analysis of the human Rho-GEFs shows that approximately 40% contain a putative PDZ-binding motif at the C-terminus. PDZ domains are protein-protein interaction domains that act as scaffolds to concentrate signaling molecules at specialized regions in the cell. We propose that the interaction between Rho-GEFs and PDZ-domain proteins is a general mechanism that controls Rho-GEF targeting and activation, helping to restrict and concentrate the exchange activity to appropriate subcellular destinations. Here, we summarize recent data that highlight the importance of these interactions in Rho-GEF regulation.
Collapse
|
259
|
Sun YJ, Nishikawa K, Yuda H, Wang YL, Osaka H, Fukazawa N, Naito A, Kudo Y, Wada K, Aoki S. Solo/Trio8, a membrane-associated short isoform of Trio, modulates endosome dynamics and neurite elongation. Mol Cell Biol 2006; 26:6923-35. [PMID: 16943433 PMCID: PMC1592863 DOI: 10.1128/mcb.02474-05] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
With DNA microarrays, we identified a gene, termed Solo, that is downregulated in the cerebellum of Purkinje cell degeneration mutant mice. Solo is a mouse homologue of rat Trio8-one of multiple Trio isoforms recently identified in rat brain. Solo/Trio8 contains N-terminal sec14-like and spectrin-like repeat domains followed by a single guanine nucleotide exchange factor 1 (GEF1) domain, but it lacks the C-terminal GEF2, immunoglobulin-like, and kinase domains that are typical of Trio. Solo/Trio8 is predominantly expressed in Purkinje neurons of the mouse brain, and expression begins following birth and increases during Purkinje neuron maturation. We identified a novel C-terminal membrane-anchoring domain in Solo/Trio8 that is required for enhanced green fluorescent protein-Solo/Trio8 localization to early endosomes (positive for both early-endosome antigen 1 [EEA1] and Rab5) in COS-7 cells and primary cultured neurons. Solo/Trio8 overexpression in COS-7 cells augmented the EEA1-positive early-endosome pool, and this effect was abolished via mutation and inactivation of the GEF domain or deletion of the C-terminal membrane-anchoring domain. Moreover, primary cultured neurons transfected with Solo/Trio8 showed increased neurite elongation that was dependent on these domains. These results suggest that Solo/Trio8 acts as an early-endosome-specific upstream activator of Rho family GTPases for neurite elongation of developing Purkinje neurons.
Collapse
Affiliation(s)
- Ying-Jie Sun
- Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
260
|
Goldshmit Y, McLenachan S, Turnley A. Roles of Eph receptors and ephrins in the normal and damaged adult CNS. ACTA ACUST UNITED AC 2006; 52:327-45. [PMID: 16774788 DOI: 10.1016/j.brainresrev.2006.04.006] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 04/21/2006] [Accepted: 04/23/2006] [Indexed: 12/19/2022]
Abstract
Injury to the central nervous system (CNS) usually results in very limited regeneration of lesioned axons, which are inhibited by the environment of the injury site. Factors that have been implicated in inhibition of axonal regeneration include myelin proteins, astrocytic gliosis and cell surface molecules that are involved in axon guidance during development. This review examines the contribution of one such family of developmental guidance molecules, the Eph receptor tyrosine kinases and their ligands, the ephrins in normal adult CNS and following injury or disease. Eph/ephrin signaling regulates axon guidance through contact repulsion during development of the CNS, inducing collapse of neuronal growth cones. Eph receptors and ephrins continue to be expressed in the adult CNS, although usually at lower levels, but are upregulated following neural injury on different cell types, including reactive astrocytes, neurons and oligodendrocytes. This upregulated expression may directly inhibit regrowth of regenerating axons; however, in addition, Eph expression also regulates astrocytic gliosis and formation of the glial scar. Therefore, Eph/ephrin signaling may inhibit regeneration by more than one mechanism and modulation of Eph receptor expression or signaling could prove pivotal in determining the outcome of injury in the adult CNS.
Collapse
Affiliation(s)
- Yona Goldshmit
- Centre for Neuroscience, The University of Melbourne, Melbourne, Vic 3010, Australia
| | | | | |
Collapse
|
261
|
Yang NY, Pasquale EB, Owen LB, Ethell IM. The EphB4 receptor-tyrosine kinase promotes the migration of melanoma cells through Rho-mediated actin cytoskeleton reorganization. J Biol Chem 2006; 281:32574-86. [PMID: 16950769 DOI: 10.1074/jbc.m604338200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Several studies have reported the up-regulation of EphB receptor-tyrosine kinases and ephrin-B ligands in a variety of tumors, suggesting a functional relation between EphB/ephrin-B signaling and tumor progression. The ability of the EphB receptors to regulate cell migration and promote angiogenesis likely contributes to tumor progression and metastasis. Here we show that EphB receptors, and especially EphB4, regulate the migration of murine melanoma cells. Highly malignant melanoma cells express the highest levels of EphB4 receptor and migrate faster than less malignant melanoma cells. Furthermore, inhibition of EphB receptor forward signaling by overexpression of a form of EphB4 lacking the cytoplasmic portion or by treatment with competitively acting soluble EphB2-Fc results in slower melanoma cell migration. In contrast, overexpression of active EphB4 significantly enhances cell migration. The effects of EphB4 receptor on cell migration and cell morphology require its kinase activity because the inhibition of EphB4 kinase activity by overexpression of kinase dead EphB4 inhibits cell migration and affects the organization of actin cytoskeleton. Activation of EphB4 receptor with its ligand ephrin-B2-Fc enhances the migratory ability of melanoma cells and increases RhoA activity, whereas inhibiting EphB receptor forward signaling decreases RhoA activity. Moreover, expression of dominant negative RhoA blocks the effects of active EphB4 on cell migration and actin organization. These data suggest that EphB4 forward signaling contributes to the high migratory ability of invasive melanoma cells by influencing RhoA-mediated actin cytoskeleton reorganization.
Collapse
Affiliation(s)
- Nai-Ying Yang
- Division of Biomedical Sciences, University of California-Riverside, Riverside, CA 92521, USA
| | | | | | | |
Collapse
|
262
|
O'Leary H, Lasda E, Bayer KU. CaMKIIbeta association with the actin cytoskeleton is regulated by alternative splicing. Mol Biol Cell 2006; 17:4656-65. [PMID: 16928958 PMCID: PMC1635389 DOI: 10.1091/mbc.e06-03-0252] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII)beta has morphogenic functions in neurons not shared by the alpha isoform. CaMKIIbeta contains three exons (v1, v3, and v4) not present in the CaMKIIalpha gene, and two of these exons (v1 and v4) are subject to differential alternative splicing. We show here that CaMKIIbeta, but not alpha, mediated bundling of F-actin filaments in vitro. Most importantly, inclusion of exon v1 was required for CaMKIIbeta association with the F-actin cytoskeleton within cells. CaMKIIbetae, which is the dominant variant around birth and lacks exon v1 sequences, failed to associate with F-actin. By contrast, CaMKIIbeta', which instead lacks exon v4, associated with F-actin as full-length CaMKIIbeta. Previous studies with CaMKIIbeta mutants have indicated a role of nonstimulated kinase activity in enhancing dendritic arborization. Here, we show that F-actin-targeted CaMKIIbeta, but not alpha, was able to phosphorylate actin in vitro even by nonstimulated basal activity in absence of Ca(2+)/CaM. In rat pancreatic islets and in skeletal muscle, the actin-associated CaMKIIbeta' and betaM were the predominant variants, respectively. Thus, cytoskeletal targeting may mediate functions of CaMKIIbeta variants also outside the nervous system.
Collapse
Affiliation(s)
| | | | - K. Ulrich Bayer
- *Department of Pharmacology
- Biomedical Sciences Program, and
- Neuroscience Program, University of Colorado Health Sciences Center, Aurora, CO 80045
| |
Collapse
|
263
|
Abstract
Glutamatergic synapses in the central nervous system are characterized by an electron-dense web underneath the postsynaptic membrane; this web is called the postsynaptic density (PSD). PSDs are composed of a dense network of several hundred proteins, creating a macromolecular complex that serves a wide range of functions. Prominent PSD proteins such as members of the MaGuk or ProSAP/Shank family build up a dense scaffold that creates an interface between clustered membrane-bound receptors, cell adhesion molecules and the actin-based cytoskeleton. Moreover, kinases, phosphatases and several proteins of different signalling pathways are specifically localized within the spine/PSD compartment. Small GTPases and regulating proteins are also enriched in PSDs being the molecular basis for regulated structural changes of cytoskeletal components within the synapse in response to external or internal stimuli, e.g. synaptic activation. This synaptic rearrangement (structural plasticity) is a rapid process and is believed to underlie learning and memory formation. The characterization of synapse/PSD proteins is especially important in the light of recent data suggesting that several mental disorders have their molecular defect at the synapse/PSD level.
Collapse
Affiliation(s)
- T M Boeckers
- Department of Anatomy and Cell Biology, Ulm University, 89081 Ulm, Germany.
| |
Collapse
|
264
|
Miyamoto Y, Yamauchi J, Tanoue A, Wu C, Mobley WC. TrkB binds and tyrosine-phosphorylates Tiam1, leading to activation of Rac1 and induction of changes in cellular morphology. Proc Natl Acad Sci U S A 2006; 103:10444-10449. [PMID: 16801538 PMCID: PMC1502477 DOI: 10.1073/pnas.0603914103] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Small GTPases of the Rho family play key roles in the formation of neuronal axons and dendrites by transducing signals from guidance cues, such as neurotrophins, to the actin cytoskeleton. However, there is little insight into the mechanism by which neurotrophins regulate Rho GTPases. Here, we show the crucial role of the ubiquitous Rac1-specific guanine nucleotide exchange factor, Tiam1 (T lymphoma invasion and metastasis 1), in transducing a neurotrophin-mediated change in cell shape. We demonstrate that BDNF, acting through TrkB, directly binds and specifically activates Tiam1 by phosphorylating Tyr-829, leading to Rac1 activation and lamellipodia formation in Cos-7 cells and increased neurite outgrowth from cortical neurons. A point mutation in Tiam1, Tyr-829 to Phe-829, blocked these BDNF-induced changes in cellular morphology. The findings are evidence of a previously uncharacterized mechanism for the activation of Tiam1 and of a role for this effector in neurotrophin-mediated signal transduction leading to changes in cellular morphology.
Collapse
Affiliation(s)
- Yuki Miyamoto
- Departments of *Neurology and Neurological Sciences and
- Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo 157-8535, Japan
| | - Junji Yamauchi
- Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo 157-8535, Japan
- Neurobiology, Stanford University School of Medicine, Stanford, CA 94305; and
| | - Akito Tanoue
- Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo 157-8535, Japan
| | - Chengbiao Wu
- Departments of *Neurology and Neurological Sciences and
| | | |
Collapse
|
265
|
Ogawa K, Wada H, Okada N, Harada I, Nakajima T, Pasquale EB, Tsuyama S. EphB2 and ephrin-B1 expressed in the adult kidney regulate the cytoarchitecture of medullary tubule cells through Rho family GTPases. J Cell Sci 2006; 119:559-70. [PMID: 16443753 DOI: 10.1242/jcs.02777] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules with well-defined functions in development, but their expression patterns and functions in many adult tissues are still largely unknown. We have detected substantial levels of the EphB2 and EphB6 receptors and the ephrin-B1 ligand in the adult mouse kidney by RT-PCR amplification. Immunolocalization experiments revealed that EphB2 is localized in the tubules of the inner and outer medulla and EphB6 is in the tubules of the outer medulla and cortex. By contrast, ephrin-B1 was detected in tubules throughout the whole nephron. Consistent with the overlapping expression of the EphB2 receptor and the ephrin-B1 ligand in the medulla, EphB2 is tyrosine-phosphorylated, and therefore activated, in the kidney. In the outer medulla, however, EphB2 signaling may be attenuated by the co-expressed kinase-inactive EphB6 receptor. Interestingly, we found that EphB signaling induces RhoA activation and Rac1 inactivation as well as cell retraction, enlargement of focal adhesions and prominent stress fibers in primary cultures of medullary tubule cells. These results suggest that EphB receptor signaling through Rho family GTPases regulates the cytoarchitecture and spatial organization of the tubule cells in the adult kidney medulla and, therefore, may affect the reabsorption ability of the kidney.
Collapse
Affiliation(s)
- Kazushige Ogawa
- Department of Veterinary Anatomy, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
| | | | | | | | | | | | | |
Collapse
|
266
|
Choi S, Ko J, Lee JR, Lee HW, Kim K, Chung HS, Kim H, Kim E. ARF6 and EFA6A regulate the development and maintenance of dendritic spines. J Neurosci 2006; 26:4811-9. [PMID: 16672654 PMCID: PMC6674147 DOI: 10.1523/jneurosci.4182-05.2006] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The cellular and molecular mechanisms underlying the development and maintenance of dendritic spines are not fully understood. ADP-ribosylation factor 6 (ARF6) is a small GTPase known to regulate actin remodeling and membrane traffic. Here, we report involvement of ARF6 and exchange factor for ARF6 (EFA6A) in the regulation of spine development and maintenance. An active form of ARF6 promotes the formation of dendritic spines at the expense of filopodia. EFA6A promotes spine formation in an ARF6 activation-dependent manner. Knockdown of ARF6 and EFA6A by small interfering RNA decreases spine formation. Live imaging indicates that ARF6 knockdown decreases the conversion of filopodia to spines and the stability of early spines. The spine-promoting effect of ARF6 is partially blocked by Rac1. ARF6 and EFA6A protect mature spines from inactivity-induced destabilization. These results suggest that ARF6 and EFA6A may regulate the conversion of filopodia to spines and the stability of both early and mature spines.
Collapse
|
267
|
Schiller MR. Coupling receptor tyrosine kinases to Rho GTPases--GEFs what's the link. Cell Signal 2006; 18:1834-43. [PMID: 16725310 DOI: 10.1016/j.cellsig.2006.01.022] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Revised: 01/19/2006] [Accepted: 04/07/2006] [Indexed: 12/20/2022]
Abstract
Rho GTPases are molecular switches involved in the regulation of many cellular processes. This review summarizes work examining how stimulation of receptor tyrosine kinases (RTKs) leads to the activation of Rho guanine nucleotide exchange factors (GEFs) and their Rho GTPase substrates. The collective findings strongly suggest that RTK signaling to Rho proteins is a general signal transduction mechanism, like RTK mediated activation of phosphatidyl inositol 3-kinase, phospholipase Cgamma, and the mitogen activated protein kinase (MAPK) pathway. More than half of the 58 known human RTKs activate at least one Rho family member. Likewise, 16 Rho GEFs directly interact with and/or are phosphorylated by a RTK. The specificity of receptor tyrosine kinase/Rho GEF signaling seems to be somewhat promiscuous. There several cases where multiple RTKs activate the same Rho GEF and where a single RTK can activate multiple Rho GEFs. Expression analysis indicates that the average human tissue contains transcripts for 33 RTKs, 34 Rho GEFs, and 14 Rho GTPases with each tissue containing a unique complement of these proteins. Given the promiscuity of RTKs for Rho GEFs, Rho GEFs for Rho GTPases, and the large number of these proteins expressed in cells, a complex combinatorial network of proteins in these families may contribute to coding specific signals and cell responses from RTKs.
Collapse
Affiliation(s)
- Martin R Schiller
- Department of Neuroscience and Partnership for Excellence in Structural Biology, University of Connecticut Health Center, Farmington, CT 06030-4301, USA.
| |
Collapse
|
268
|
Regalado MP, Terry-Lorenzo RT, Waites CL, Garner CC, Malenka RC. Transsynaptic signaling by postsynaptic synapse-associated protein 97. J Neurosci 2006; 26:2343-57. [PMID: 16495462 PMCID: PMC6674804 DOI: 10.1523/jneurosci.5247-05.2006] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The molecular mechanisms by which postsynaptic modifications lead to precisely coordinated changes in presynaptic structure and function are primarily unknown. To address this issue, we examined the presynaptic consequences of postsynaptic expression of members of the membrane-associated guanylate kinase family of synaptic scaffolding proteins. Postsynaptic expression of synapse-associated protein 97 (SAP97) increased presynaptic protein content and active zone size to a greater extent than comparable amounts of postsynaptic PSD-95 (postsynaptic density-95) or SAP102. In addition, postsynaptic expression of SAP97 enhanced presynaptic function, as measured by increased FM4-64 dye uptake. The structural presynaptic effects of postsynaptic SAP97 required ligand binding through two of its PDZ (PSD-95/Discs large/zona occludens-1) domains as well as intact N-terminal and guanylate kinase domains. Expression of SAP97 recruited a complex of additional postsynaptic proteins to synapses including glutamate receptor 1, Shank1a, SPAR (spine-associated RapGAP), and proSAP2. Furthermore, inhibition of several different transsynaptic signaling proteins including cadherins, integrins, and EphB receptor/ephrinB significantly reduced the presynaptic growth caused by postsynaptic SAP97. These results suggest that SAP97 may play a central role in the coordinated growth of synapses during development and plasticity by recruiting a complex of postsynaptic proteins that enhances presynaptic terminal growth and function via multiple transsynaptic molecular interactions.
Collapse
|
269
|
Jassen AK, Yang H, Miller GM, Calder E, Madras BK. Receptor regulation of gene expression of axon guidance molecules: implications for adaptation. Mol Pharmacol 2006; 70:71-7. [PMID: 16595738 DOI: 10.1124/mol.105.021998] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Axon guidance molecules, critical for neurodevelopment, are also implicated in morphological and other neurodaptative changes mediated by physiological or pharmacological events in adult brain. As an example, the psychostimulant cocaine markedly alters axon guidance molecules in adult brain of cocaine-treated rats. To decipher a potential link between drug-induced activation of G-protein-coupled receptors (GPCRs) and modulation of axon guidance molecules, we investigated whether GPCR activity in a SK-N-MC human neuroepithelioma cell line (which expresses low levels of D1 dopamine receptors) affects gene expression of axon guidance molecules (semaphorins, ephrins, netrins, and their receptors). Using real-time polymerase chain reaction, we identified 17 of 26 axon guidance molecules in these cells, with varying levels of expression. Forskolin, which raised intracellular cAMP levels 340%, increased EphA5, EphB2, and Neuropilin1 expression, paralleling reported changes in the rat hippocampus after cocaine treatment. The dopamine receptor agonist dihydrexidine, which raised cAMP levels 22%, promoted regulatory changes in EphrinA1, EphrinA5, EphB1, DCC, and Semaphorin3C, whereas (+/-)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF81297) altered EphA5, EphrinA1, EphrinA5, and neuropilin1. cAMP and other signal transduction pathways may regulate gene expression of axon guidance molecules, potentially linking monoamine receptor activation to signal transduction cascades, transcriptional regulation of axon guidance molecules, and alterations in neural networks.
Collapse
Affiliation(s)
- Amy K Jassen
- Department of Psychiatry, Harvard Medical School, Division of Neurochemistry, New England Regional Primate Research Center, 1 Pine Hill Drive, Southborough, MA 01772-9102, USA
| | | | | | | | | |
Collapse
|
270
|
Zhang H, Webb DJ, Asmussen H, Niu S, Horwitz AF. A GIT1/PIX/Rac/PAK signaling module regulates spine morphogenesis and synapse formation through MLC. J Neurosci 2006; 25:3379-88. [PMID: 15800193 PMCID: PMC6724907 DOI: 10.1523/jneurosci.3553-04.2005] [Citation(s) in RCA: 273] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Three of seven recently identified genes mutated in nonsyndromic mental retardation are involved in Rho family signaling. Two of the gene products, alpha-p-21-activated kinase (PAK) interacting exchange factor (alphaPIX) and PAK3, form a complex with the synaptic adaptor protein G-protein-coupled receptor kinase-interacting protein 1 (GIT1). Using an RNA interference approach, we show that GIT1 is critical for spine and synapse formation. We also show that Rac is locally activated in dendritic spines using fluorescence resonance energy transfer. This local activation of Rac is regulated by PIX, a Rac guanine nucleotide exchange factor. PAK1 and PAK3 serve as downstream effectors of Rac in regulating spine and synapse formation. Active PAK promotes the formation of spines and dendritic protrusions, which correlates with an increase in the number of excitatory synapses. These effects are dependent on the kinase activity of PAK, and PAK functions through phosphorylating myosin II regulatory light chain (MLC). Activated MLC causes an increase in dendritic spine and synapse formation, whereas inhibiting myosin ATPase activity results in decreased spine and synapse formation. Finally, both activated PAK and activated MLC can rescue the defects of GIT1 knockdown, suggesting that PAK and MLC are downstream of GIT1 in regulating spine and synapse formation. Our results point to a signaling complex, consisting of GIT1, PIX, Rac, and PAK, that plays an essential role in the regulation of dendritic spine and synapse formation and provides a potential mechanism by which alphaPIX and PAK3 mutations affect cognitive functions in mental retardation.
Collapse
Affiliation(s)
- Huaye Zhang
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA
| | | | | | | | | |
Collapse
|
271
|
Georgakopoulos A, Litterst C, Ghersi E, Baki L, Xu C, Serban G, Robakis NK. Metalloproteinase/Presenilin1 processing of ephrinB regulates EphB-induced Src phosphorylation and signaling. EMBO J 2006; 25:1242-52. [PMID: 16511561 PMCID: PMC1422162 DOI: 10.1038/sj.emboj.7601031] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2005] [Revised: 02/09/2006] [Indexed: 01/08/2023] Open
Abstract
Bidirectional signaling triggered by interacting ephrinB receptors (EphB) and ephrinB ligands is crucial for development and function of the vascular and nervous systems. A signaling cascade triggered by this interaction involves activation of Src kinase and phosphorylation of ephrinB. The mechanism, however, by which EphB activates Src in the ephrinB-expressing cells is unknown. Here we show that EphB stimulates a metalloproteinase cleavage of ephrinB2, producing a carboxy-terminal fragment that is further processed by PS1/gamma-secretase to produce intracellular peptide ephrinB2/CTF2. This peptide binds Src and inhibits its association with inhibitory kinase Csk, allowing autophosphorylation of Src at residue tyr418. EphrinB2/CTF2-activated Src phosphorylates ephrinB2 and inhibits its processing by gamma-secretase. These data show that the PS1/gamma-secretase system controls Src activation and ephrinB phosphorylation by regulating production of Src activator ephrinB2/CTF2. Accordingly, gamma-secretase inhibitors prevented the EphB-induced sprouting of endothelial cells and the recruitment of Grb4 to ephrinB. PS1 FAD and gamma-secretase dominant-negative mutants inhibited the EphB-induced cleavage of ephrinB2 and Src autophosphorylation, raising the possibility that FAD mutants interfere with the functions of Src and ephrinB2 in the CNS.
Collapse
Affiliation(s)
| | - Claudia Litterst
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| | - Enrico Ghersi
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| | - Lia Baki
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| | - ChiJie Xu
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| | - Geo Serban
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| | - Nikolaos K Robakis
- Departments of Psychiatry and Neuroscience, Mount Sinai School of Medicine, NYU, New York, NY, USA
| |
Collapse
|
272
|
Calabrese B, Wilson MS, Halpain S. Development and regulation of dendritic spine synapses. Physiology (Bethesda) 2006; 21:38-47. [PMID: 16443821 DOI: 10.1152/physiol.00042.2005] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Dendritic spines are small protrusions from neuronal dendrites that form the postsynaptic component of most excitatory synapses in the brain. They play critical roles in synaptic transmission and plasticity. Recent advances in imaging and molecular technologies reveal that spines are complex, dynamic structures that contain a dense array of cytoskeletal, transmembrane, and scaffolding molecules. Several neurological and psychiatric disorders exhibit dendritic spine abnormalities.
Collapse
Affiliation(s)
- Barbara Calabrese
- Department of Cell Biology and Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, USA
| | | | | |
Collapse
|
273
|
Abstract
Glutamatergic synapses switch from nonspiny synapses to become dendritic spines during early neuronal development. Here, we report that the lack of sufficient Rac1, a small RhoGTPase, contributes to the absence of spinogenesis in immature neurons. The overexpression of green fluorescence protein-tagged wild-type Rac1 initiated the formation of dendritic spines in cultured dissociated hippocampal neurons younger than 11 d in vitro, indicating that Rac1 is likely one of the missing pieces responsible for the lack of spines in immature neurons. The overexpression of wild-type Rac1 also induced the clustering of AMPA receptors (AMPARs) and increased the amplitude of miniature EPSCs (mEPSCs). The expression of constitutively active Rac1 induced the formation of unusually large synapses with large amounts of AMPAR clusters. Also, our live imaging experiments revealed that the contact of an axon induced the clustering of Rac1, and subsequent morphological changes led to spinogenesis. Additionally, the overexpression of wild-type Rac1 and constitutively active Rac1 increased the size of preexisting spines and the amplitude of mEPSCs in mature neurons (>21 d in vitro) within 24 h after transfection. Together, these results indicate that activation of Rac1 enhances excitatory synaptic transmission by recruiting AMPARs to synapses during spinogenesis, thus providing a mechanistic link between presynaptic and postsynaptic developmental changes. Furthermore, we show that Rac1 has two distinct roles at different stages of neuronal development. The activation of Rac1 initiates spinogenesis at an early stage and regulates the function and morphology of preexisting spines at a later stage.
Collapse
Affiliation(s)
- Katie M Wiens
- Department of Neuroscience, The University of Minnesota, Minneapolis, Minnesota 55455, USA
| | | | | |
Collapse
|
274
|
Yoshizawa M, Kawauchi T, Sone M, Nishimura YV, Terao M, Chihama K, Nabeshima YI, Hoshino M. Involvement of a Rac activator,P-Rex1, in neurotrophin-derived signaling and neuronal migration. J Neurosci 2006; 25:4406-19. [PMID: 15858067 PMCID: PMC6725123 DOI: 10.1523/jneurosci.4955-04.2005] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Rho-family GTPases play key roles in regulating cytoskeletal reorganization, contributing to many aspects of nervous system development. Their activities are known to be regulated by guanine nucleotide exchange factors (GEFs), in response to various extracellular cues. P-Rex1, a GEF for Rac, has been mainly investigated in neutrophils, in which this molecule contributes to reactive oxygen species formation. However, its role in the nervous system is essentially unknown. Here we describe the expression profile and a physiological function of P-Rex1 in nervous system development. In situ hybridization revealed that P-Rex1 is dynamically expressed in a variety of cells in the developing mouse brain, including some cortical and DRG neurons. In migrating neurons in the intermediate zone, P-Rex1 protein was found to localize in the leading process and adjacent cytoplasmic region. When transfected in pheochromocytoma PC12 cells, P-Rex1 can be activated by NGF, causing an increase in GTP-bound Rac1 and cell motility. Deletion analyses suggested roles for distinct domains of this molecule. Experiments using a P-Rex1 mutant lacking the Dbl-homology domain, a dominant-negative-like form, and small interfering RNA showed that endogenous P-Rex1 was involved in cell migration of PC12 cells and primary cultured neurons from the embryonic day 14 cerebral cortices, induced by extracellular stimuli (NGF, BDNF, and epidermal growth factor). Furthermore, in utero electroporation of the mutant protein into the embryonic cerebral cortex perturbed radial neuronal migration. These findings suggest that P-Rex1, which is expressed in a variety of cell types, is activated by extracellular cues such as neurotrophins and contributes to neuronal migration in the developing nervous system.
Collapse
Affiliation(s)
- Masato Yoshizawa
- Department of Pathology and Tumor Biology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan
| | | | | | | | | | | | | | | |
Collapse
|
275
|
Nishimura T, Yamaguchi T, Tokunaga A, Hara A, Hamaguchi T, Kato K, Iwamatsu A, Okano H, Kaibuchi K. Role of numb in dendritic spine development with a Cdc42 GEF intersectin and EphB2. Mol Biol Cell 2006; 17:1273-85. [PMID: 16394100 PMCID: PMC1382316 DOI: 10.1091/mbc.e05-07-0700] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Revised: 11/15/2005] [Accepted: 12/27/2005] [Indexed: 12/22/2022] Open
Abstract
Numb has been implicated in cortical neurogenesis during nervous system development, as a result of its asymmetric partitioning and antagonizing Notch signaling. Recent studies have revealed that Numb functions in clathrin-dependent endocytosis by binding to the AP-2 complex. Numb is also expressed in postmitotic neurons and plays a role in axonal growth. However, the functions of Numb in later stages of neuronal development remain unknown. Here, we report that Numb specifically localizes to dendritic spines in cultured hippocampal neurons and is implicated in dendritic spine morphogenesis, partially through the direct interaction with intersectin, a Cdc42 guanine nucleotide exchange factor (GEF). Intersectin functions as a multidomain adaptor for proteins involved in endocytosis and cytoskeletal regulation. Numb enhanced the GEF activity of intersectin toward Cdc42 in vivo. Expression of Numb or intersectin caused the elongation of spine neck, whereas knockdown of Numb and Numb-like decreased the protrusion density and its length. Furthermore, Numb formed a complex with EphB2 receptor-type tyrosine kinase and NMDA-type glutamate receptors. Knockdown of Numb suppressed the ephrin-B1-induced spine development and maturation. These results highlight a role of Numb for dendritic spine development and synaptic functions with intersectin and EphB2.
Collapse
Affiliation(s)
- Takashi Nishimura
- Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University, Nagoya, Aichi 466-8550, Japan
| | | | | | | | | | | | | | | | | |
Collapse
|
276
|
Rodenas-Ruano A, Perez-Pinzon MA, Green EJ, Henkemeyer M, Liebl DJ. Distinct roles for ephrinB3 in the formation and function of hippocampal synapses. Dev Biol 2006; 292:34-45. [PMID: 16466709 DOI: 10.1016/j.ydbio.2006.01.004] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2005] [Revised: 12/21/2005] [Accepted: 01/03/2006] [Indexed: 12/20/2022]
Abstract
The transmembrane ephrinB ligands and their Eph receptor tyrosine kinases are known to regulate excitatory synaptic functions in the hippocampus. In the CA3-CA1 synapse, ephrinB ligands are localized to the post-synaptic membrane, while their cognate Eph receptors are presumed to be pre-synaptic. Interaction of ephrinB molecules with Eph receptors leads to changes in long-term potentiation (LTP), which has been reported to be mediated by reverse signaling into the post-synaptic membrane. Here, we demonstrate that the cytoplasmic domain of ephrinB3 and hence reverse signaling is not required for ephrinB dependent learning and memory tasks or for LTP of these synapses. Consistent with previous reports, we find that ephrinB3(KO) null mutant mice exhibit a striking reduction in CA3-CA1 LTP that is associated with defective learning and memory tasks. We find the null mutants also show changes in both pre- and post-synaptic proteins including increased levels of synapsin and synaptobrevin and reduced levels of NMDA receptor subunits. These abnormalities are not observed in ephrinB3(lacZ) reverse signaling mutants that specifically delete the ephrinB3 intracellular region, supporting a cytoplasmic domain-independent forward signaling role for ephrinB3 in these processes. We also find that both ephrinB3(KO) and ephrinB3(lacZ) mice show an increased number of excitatory synapses, demonstrating a cytoplasmic-dependent reverse signaling role of ephrinB3 in regulating synapse number. Together, these data suggest that ephrinB3 may act like a receptor to transduce reverse signals to regulate the number of synapses formed in the hippocampus, and that it likely acts to stimulate forward signaling to modulate a number of other proteins involved in synaptic activity and learning/memory.
Collapse
Affiliation(s)
- Alma Rodenas-Ruano
- Neuroscience Program, University of Miami School of Medicine, Miami, FL 33136, USA
| | | | | | | | | |
Collapse
|
277
|
Tada T, Sheng M. Molecular mechanisms of dendritic spine morphogenesis. Curr Opin Neurobiol 2006; 16:95-101. [PMID: 16361095 DOI: 10.1016/j.conb.2005.12.001] [Citation(s) in RCA: 512] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Accepted: 12/02/2005] [Indexed: 11/29/2022]
Abstract
Excitatory synapses are formed on dendritic spines, postsynaptic structures that change during development and in response to synaptic activity. Once mature, however, spines can remain stable for many months. The molecular mechanisms that control the formation and elimination, motility and stability, and size and shape of dendritic spines are being revealed. Multiple signaling pathways, particularly those involving Rho and Ras family small GTPases, converge on the actin cytoskeleton to regulate spine morphology and dynamics bidirectionally. Numerous cell surface receptors, scaffold proteins and actin binding proteins are concentrated in spines and engaged in spine morphogenesis.
Collapse
Affiliation(s)
- Tomoko Tada
- The Picower Institute for Learning and Memory, RIKEN-MIT Neuroscience Research Center, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | | |
Collapse
|
278
|
Buttery P, Beg AA, Chih B, Broder A, Mason CA, Scheiffele P. The diacylglycerol-binding protein alpha1-chimaerin regulates dendritic morphology. Proc Natl Acad Sci U S A 2006; 103:1924-9. [PMID: 16446429 PMCID: PMC1413663 DOI: 10.1073/pnas.0510655103] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The morphological and functional differentiation of neuronal dendrites is controlled through transcriptional programs and cell-cell signaling. Synaptic activity is thought to play an important role in the maturation of dendritic arbors, but the signaling pathways that couple neuronal activity and morphological changes in dendrites are not well understood. We explored the function of alpha1-chimaerin, a neuronal diacylglycerol-binding protein with a Rho GTPase-activating protein domain that inactivates Rac1. We find that stimulation of phospholipase Cbeta-coupled cell surface receptors recruits alpha1-chimaerin to the plasma membrane of cultured hippocampal neurons. We further show that alpha1-chimaerin protein levels are controlled by synaptic activity and that increased alpha1-chimaerin expression results in the pruning of dendritic spines and branches. This pruning activity requires both the diacylglycerol-binding and Rac GTPase-activating protein activity of alpha1-chimaerin. Suppression of alpha1-chimaerin expression resulted in increased process growth from the dendritic shaft and from spine heads. Our data suggest that alpha1-chimaerin is an activity-regulated Rho GTPase regulator that is activated by phospholipase Cbeta-coupled cell surface receptors and contributes to pruning of dendritic arbors.
Collapse
Affiliation(s)
- Philip Buttery
- *Department of Pathology and Cell Biology, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 14-509, 630 West 168th Street, New York, NY 10032; and
| | - Asim A. Beg
- Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 11-511, 630 West 168th Street, New York, NY 10032
| | - Ben Chih
- Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 11-511, 630 West 168th Street, New York, NY 10032
| | - Arkady Broder
- Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 11-511, 630 West 168th Street, New York, NY 10032
| | - Carol A. Mason
- *Department of Pathology and Cell Biology, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 14-509, 630 West 168th Street, New York, NY 10032; and
| | - Peter Scheiffele
- Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, College of Physicians and Surgeons, P&S 11-511, 630 West 168th Street, New York, NY 10032
- To whom correspondence should be addressed. E-mail:
| |
Collapse
|
279
|
Xie Z, Huganir RL, Penzes P. Activity-dependent dendritic spine structural plasticity is regulated by small GTPase Rap1 and its target AF-6. Neuron 2006; 48:605-18. [PMID: 16301177 DOI: 10.1016/j.neuron.2005.09.027] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2005] [Revised: 09/16/2005] [Accepted: 09/28/2005] [Indexed: 12/11/2022]
Abstract
Activity-dependent remodeling of dendritic spines is essential for neural circuit development and synaptic plasticity, but the mechanisms that coordinate synaptic structural and functional plasticity are not well understood. Here we investigate the signaling pathways that enable excitatory synapses to undergo activity-dependent structural modifications. We report that activation of NMDA receptors in cultured cortical neurons induces spine morphogenesis and activation of the small GTPase Rap1. Rap1 bimodally regulates spine morphology: activated Rap1 recruits the PDZ domain-containing protein AF-6 to the plasma membrane and induces spine neck elongation, while inactive Rap1 dissociates AF-6 from the membrane and induces spine enlargement. Rap1 also regulates spine content of AMPA receptors: thin spines induced by Rap1 activation have reduced GluR1-containing AMPA receptor content, while large spines induced by Rap1 inactivation are rich in AMPA receptors. These results identify a signaling pathway that regulates activity-dependent synaptic structural plasticity and coordinates it with functional plasticity.
Collapse
Affiliation(s)
- Zhong Xie
- Department of Physiology, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Chicago, Illinois 60611
| | | | | |
Collapse
|
280
|
Xiao D, Miller GM, Jassen A, Westmoreland SV, Pauley D, Madras BK. Ephrin/Eph receptor expression in brain of adult nonhuman primates: Implications for neuroadaptation. Brain Res 2006; 1067:67-77. [PMID: 16360648 DOI: 10.1016/j.brainres.2005.10.073] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Accepted: 10/25/2005] [Indexed: 11/23/2022]
Abstract
In developing brain, Eph receptors and their ephrin ligands (Ephs/ephrins) are implicated in facilitating topographic guidance of a number of pathways, including the nigrostriatal and mesolimbic dopamine (DA) pathways. In adult rodent brain, these molecules are implicated in neuronal plasticity associated with learning and memory. Cocaine significantly alters the expression of select members of this family of axonal guidance molecules, implicating Ephs, ephrins in drug-induced neuroadaptation. The potential contribution of Ephs, ephrins to cocaine-induced reorganization of striatal circuitry brain in primates [Saka, E., Goodrich, C., Harlan, P., Madras, B.K., Graybiel, A.M., 2004. Repetitive behaviors in monkeys are linked to specific striatal activation patterns. J. Neurosci. 24, 7557-7565] is unknown because there are no documented reports of Eph/ephrin expression or function in adult primate brain. We now report that brains of adult old and new world monkeys express mRNA encoding EphA4 receptor and ephrin-B2 ligand, implicated in topographic guidance of dopamine and striatal neurons during development. Their encoded proteins distributed highly selectively in regions of adult monkey brain. EphA4 mRNA levels were prominent in the DA-rich caudate/putamen, nucleus accumbens and globus pallidus, as well as the medial and orbitofrontal cortices, hippocampus, amygdala, thalamus and cerebellum. Immunocytochemical localization of EphA4 protein revealed discrete expression in caudate/putamen, globus pallidus, substantia nigra, cerebellar Purkinje cells, pyramidal cells of frontal cortices (layers II, III and V) and the subgranular zone of the hippocampus. Evidence for EphA4 expression in dopamine neurons emerged from colocalization with tyrosine-hydroxylase-positive terminals in striatum and substantia nigra and ventral tegmental area cell bodies. The association of axonal guidance molecules with drug-induced reorganization of adult primate brain circuitry warrants investigation.
Collapse
Affiliation(s)
- Danqing Xiao
- Department of Psychiatry, Harvard Medical School, Division of Neurochemistry, New England Primate Research Center, Southborough, MA 01772-9102, USA
| | | | | | | | | | | |
Collapse
|
281
|
Koh CG. Rho GTPases and Their Regulators in Neuronal Functions and Development. Neurosignals 2006; 15:228-37. [PMID: 17409776 DOI: 10.1159/000101527] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Accepted: 02/15/2007] [Indexed: 12/16/2022] Open
Abstract
Neurons are specialized cell types which send out processes in order to communicate with other cells, which can be immediate neighbors or whose cell bodies are far distant. Neuronal morphology as in all cells is determined in large part through the regulation of the cytoskeleton. One of the key regulators of the actin cytoskeleton is the Rho family of GTPases. The Rho GTPases function as molecular switches to turn on or off downstream biochemical pathways depending on the stimuli. Their activities and their regulation are controlled by many other proteins such as the guanine nucleotide exchange factors and the GTPase-activating proteins. The activities of some of the Rho family members are reported to be antagonistic to one another. In general, Rac and Cdc42 promote neurite outgrowth while RhoA stimulates retraction. The balance of these opposing activities of the different Rho GTPases is crucial for the morphology and function of the neurons.
Collapse
Affiliation(s)
- Cheng-Gee Koh
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
| |
Collapse
|
282
|
Moeller ML, Shi Y, Reichardt LF, Ethell IM. EphB Receptors Regulate Dendritic Spine Morphogenesis through the Recruitment/Phosphorylation of Focal Adhesion Kinase and RhoA Activation. J Biol Chem 2006; 281:1587-98. [PMID: 16298995 DOI: 10.1074/jbc.m511756200] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Dendritic filopodia are small protrusions on the surface of neuronal dendrites that transform into dendritic spines upon synaptic contact with axon terminals. The formation of dendritic spines is a critical aspect of synaptic development. Dendritic spine morphogenesis is characterized by filopodia shortening followed by the formation of mature mushroom-shaped spines. Here we show that activation of the EphB receptor tyrosine kinases in cultured hippocampal neurons by their ephrinB ligands induces morphogenesis of dendritic filopodia into dendritic spines. This appears to occur through assembly of an EphB-associated protein complex that includes focal adhesion kinase (FAK), Src, Grb2, and paxillin and the subsequent activations of FAK, Src, paxillin, and RhoA. Furthermore, Cre-mediated knock-out of loxP-flanked fak or RhoA inhibition blocks EphB-mediated morphogenesis of dendritic filopodia. Finally, EphB-mediated RhoA activation is disrupted by FAK knock-down. These data suggest that EphB receptors are upstream regulators of FAK in dendritic filopodia and that FAK-mediated RhoA activation contributes to assembly of actin filaments in dendritic spines.
Collapse
Affiliation(s)
- Michael L Moeller
- Division of Biomedical Sciences, University of California Riverside, Riverside, California 92521, USA
| | | | | | | |
Collapse
|
283
|
El-Hashash AHK, Kimber SJ. PTHrP induces changes in cell cytoskeleton and E-cadherin and regulates Eph/Ephrin kinases and RhoGTPases in murine secondary trophoblast cells. Dev Biol 2005; 290:13-31. [PMID: 16375886 DOI: 10.1016/j.ydbio.2005.10.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 10/03/2005] [Accepted: 10/06/2005] [Indexed: 10/25/2022]
Abstract
The differentiation of murine trophoblast giant cells (TGCs) is well characterised at the molecular level and, to some extent, the cellular level. Currently, there is a rudimentary understanding about factors regulating the cellular differentiation of secondary TGCs. Using day 8.5 p.c.-ectoplacental cone (EPC) explant in serum-free culture, we have found parathyroid hormone-related protein (PTHrP) to regulate cellular changes during TGC differentiation. PTHrP greatly stimulated the formation and organisation of actin stress fibres and actin expression in trophoblast outgrowth. This coincided with changing cell shape into a flattened/fibroblastic morphology, suppression of E-cadherin expression, and increased cell spreading in culture. PTHrP also increased the nuclear staining of beta-catenin and, similar to activator protein-2gamma (AP-2gamma), showed microtubule-dependent nuclear localisation in vitro. These cellular and behavioural changes correlated with changes in the expression of RhoGTPases and in both expression and phosphorylation of Eph/Ephrin kinases. The effects of PTHrP on trophoblast cellular differentiation were abolished after blocking its action. In conclusion, PTHrP provides an excellent example of the extrinsic factors that, through their network of activities, plays an important role in cellular differentiation of secondary TGCs.
Collapse
Affiliation(s)
- Ahmed H K El-Hashash
- Faculty of Life Sciences, University of Manchester, 3.239 Stopford Building, Oxford Road, Manchester M13 9PT, UK.
| | | |
Collapse
|
284
|
Alfonso J, Fernández ME, Cooper B, Flugge G, Frasch AC. The stress-regulated protein M6a is a key modulator for neurite outgrowth and filopodium/spine formation. Proc Natl Acad Sci U S A 2005; 102:17196-201. [PMID: 16286650 PMCID: PMC1287971 DOI: 10.1073/pnas.0504262102] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Accepted: 10/05/2005] [Indexed: 12/11/2022] Open
Abstract
Neuronal remodeling is a fundamental process by which the brain responds to environmental influences, e.g., during stress. In the hippocampus, chronic stress causes retraction of dendrites in CA3 pyramidal neurons. We have recently identified the glycoprotein M6a as a stress-responsive gene in the hippocampal formation. This gene is down-regulated in the hippocampus of both socially and physically stressed animals, and this effect can be reversed by antidepressant treatment. In the present work, we analyzed the biological function of the M6a protein. Immunohistochemistry showed that the M6a protein is abundant in all hippocampal subregions, and subcellular analysis in primary hippocampal neurons revealed its presence in membrane protrusions (filopodia/spines). Transfection experiments revealed that M6a overexpression induces neurite formation and increases filopodia density in hippocampal neurons. M6a knockdown with small interference RNA methodology showed that M6a low-expressing neurons display decreased filopodia number and a lower density of synaptophysin clusters. Taken together, our findings indicate that M6a plays an important role in neurite/filopodium outgrowth and synapse formation. Therefore, reduced M6a expression might be responsible for the morphological alterations found in the hippocampus of chronically stressed animals. Potential mechanisms that might explain the biological effects of M6a are discussed.
Collapse
Affiliation(s)
- Julieta Alfonso
- Instituto de Investigaciones Biotecnológicas-INTECH Universidad Nacional Gral. San Martín y Consejo Nacional de Investigaciones Científicas y Técnicas, 1650 San Martín, Argentina.
| | | | | | | | | |
Collapse
|
285
|
Tavazoie SF, Alvarez VA, Ridenour DA, Kwiatkowski DJ, Sabatini BL. Regulation of neuronal morphology and function by the tumor suppressors Tsc1 and Tsc2. Nat Neurosci 2005; 8:1727-34. [PMID: 16286931 DOI: 10.1038/nn1566] [Citation(s) in RCA: 370] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2005] [Accepted: 09/15/2005] [Indexed: 12/31/2022]
Abstract
Mutations in the TSC1 or TSC2 tumor suppressor genes lead to tuberous sclerosis complex (TSC), a dominant hamartomatous disorder that often presents with mental retardation, epilepsy and autism. The etiology of these neurological symptoms is unclear and the function of the TSC pathway in neurons is unknown. We found that in post-mitotic, hippocampal pyramidal neurons of mice and rats, loss of Tsc1 or Tsc2 triggered enlargement of somas and dendritic spines and altered the properties of glutamatergic synapses. Furthermore, loss of a single copy of the Tsc1 gene was sufficient to perturb dendritic spine structure. Morphological changes required regulation of the actin-depolymerization factor cofilin at a conserved LIM-kinase phosphorylation site, the phosphorylation of which was increased by loss of Tsc2. Thus, the TSC pathway regulates growth and synapse function in neurons, and perturbations of neuronal structure and function are likely to contribute to the pathogenesis of the neurological symptoms of TSC.
Collapse
Affiliation(s)
- Sohail F Tavazoie
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts 02115, USA
| | | | | | | | | |
Collapse
|
286
|
Abstract
Synapses are highly specialized intercellular junctions that mediate the transmission of information between axons and target cells. A fundamental property of synapses is their ability to modify the efficacy of synaptic communication through various forms of synaptic plasticity. Recent developments in imaging techniques have revealed that synapses exhibit a high degree of morphological plasticity under basal conditions and also in response to neuronal activity that induces alterations in synaptic strength. The underlying molecular basis for this morphological plasticity has attracted much attention, yet its functional significance to the mechanisms of synaptic transmission and synaptic plasticity remains elusive. These morphological changes ultimately require the dynamic actin cytoskeleton, which is the major structural component of synapses. Delineating the physiological roles of the actin cytoskeleton in supporting synaptic transmission and synaptic plasticity, therefore, paves the way for gaining molecular insights into when and how synaptic machineries couple synapse form and function.
Collapse
Affiliation(s)
- Christian Dillon
- MRC Cell Biology Unit and Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, United Kingdom.
| | | |
Collapse
|
287
|
Abstract
The formation of synapses in the vertebrate central nervous system is a complex process that occurs over a protracted period of development. Recent work has begun to unravel the mysteries of synaptogenesis, demonstrating the existence of multiple molecules that influence not only when and where synapses form but also synaptic specificity and stability. Some of these molecules act at a distance, steering axons to their correct receptive fields and promoting neuronal differentiation and maturation, whereas others act at the time of contact, providing positional information about the appropriateness of targets and/or inductive signals that trigger the cascade of events leading to synapse formation. In addition, correlated synaptic activity provides critical information about the appropriateness of synaptic connections, thereby influencing synapse stability and elimination. Although synapse formation and elimination are hallmarks of early development, these processes are also fundamental to learning, memory, and cognition in the mature brain.
Collapse
Affiliation(s)
- Clarissa L Waites
- Department of Psychiatry and Behavioral Science, Nancy Pritzker Laboratory, Stanford University, Palo Alto, CA 94304-5485, USA.
| | | | | |
Collapse
|
288
|
Parent AT, Barnes NY, Taniguchi Y, Thinakaran G, Sisodia SS. Presenilin attenuates receptor-mediated signaling and synaptic function. J Neurosci 2005; 25:1540-9. [PMID: 15703408 PMCID: PMC6725985 DOI: 10.1523/jneurosci.3850-04.2005] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Presenilin (PS) plays an essential role in intramembranous gamma-secretase processing of amyloid precursor protein (APP) and several membrane-bound proteins. Here we report that selective accumulation of a membrane-tethered deleted in colorectal cancer (DCC) derivative (DCC-alpha) correlates with extensive neurite outgrowth in transfected neuroblastoma cells and axodendritic connectivity associated with increased spine density in cortical neurons derived from PS1(-/-) embryos, as well as wild-type neurons treated with gamma-secretase inhibitors. cAMP-dependent signaling was also increased in both the neuroblastoma and cortical neuron systems. As a physiological consequence of increases in axodendritic connectivity and in the magnitude of cAMP-dependent signaling, short- and long-term glutamatergic synaptic transmission was enhanced in PS-deficient neurons. Together, these results demonstrate for the first time that PS-mediated gamma-secretase activity attenuates receptor-mediated intracellular signaling pathways that are critical in regulating glutamatergic synaptic transmission and memory processes.
Collapse
Affiliation(s)
- Angèle T Parent
- Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
| | | | | | | | | |
Collapse
|
289
|
Maruoka H, Konno D, Hori K, Sobue K. Collaboration of PSD-Zip70 with its binding partner, SPAR, in dendritic spine maturity. J Neurosci 2005; 25:1421-30. [PMID: 15703396 PMCID: PMC6726009 DOI: 10.1523/jneurosci.3920-04.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Recent studies have reported on the molecular mechanisms underlying dendritic spine (spine) dynamics. Because most of these studies investigated spine dynamics by overexpressing constitutively active or dominant-negative PSD (postsynaptic density) proteins in cultured mature neurons, the results represent the enlargement of mature spines or their return to an immature state. Here, we developed the technique of in utero electroporation to investigate spine dynamics. Using this technique, we demonstrated the suppression of spine maturation by the C-terminal variants of PSD-Zip70 in vitro and in vivo. Transient overexpression of the C terminus of PSD-Zip70 and knock-down of PSD-Zip70 also displayed the destabilization of mature spines. We further found the PSD-Zip70 and SPAR (spine-associated RapGAP) interaction via the short C-terminal region of PSD-Zip70 and the GK-binding domain of SPAR. In association with immature spines induced by overexpression of the PSD-Zip70 C terminus or knock-down of PSD-Zip70, SPAR lost its spine localization. Overexpression of the GK-binding domain of SPAR also induced to form immature spines without affecting the localization of PSD-Zip70 in the small heads of filopodial spines. Our results suggest that PSD-Zip70 in collaboration with SPAR is critically involved in spine maturity, especially in the mature spine formation and the maintenance of spine maturity.
Collapse
Affiliation(s)
- Hisato Maruoka
- Department of Neuroscience, Osaka University Graduate School of Medicine, Suita City, Osaka 565-0871, Japan
| | | | | | | |
Collapse
|
290
|
Ryan XP, Alldritt J, Svenningsson P, Allen PB, Wu GY, Nairn AC, Greengard P. The Rho-specific GEF Lfc interacts with neurabin and spinophilin to regulate dendritic spine morphology. Neuron 2005; 47:85-100. [PMID: 15996550 DOI: 10.1016/j.neuron.2005.05.013] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2003] [Revised: 01/24/2004] [Accepted: 05/06/2005] [Indexed: 01/07/2023]
Abstract
Neurabin and spinophilin are homologous protein phosphatase 1 and actin binding proteins that regulate dendritic spine function. A yeast two-hybrid analysis using the coiled-coil domain of neurabin revealed an interaction with Lfc, a Rho GEF. Lfc was highly expressed in brain, where it interacted with either neurabin or spinophilin. In neurons, Lfc was largely found in the shaft of dendrites in association with microtubules but translocated to spines upon neuronal stimulation. Moreover, expression of Lfc resulted in reduction in spine length and size. Both the translocation and the effect on spine morphology depended on the coiled-coil domain of Lfc. Coexpression of neurabin or spinophilin with Lfc resulted in their clustering together with F-actin, a process that depended on Rho activity. Thus, interaction between Lfc and neurabin/spinophilin selectively regulates Rho-dependent organization of F-actin in spines and is a link between the microtubule and F-actin cytoskeletons in dendrites.
Collapse
Affiliation(s)
- Xiaozhou P Ryan
- Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
| | | | | | | | | | | | | |
Collapse
|
291
|
Steven R, Zhang L, Culotti J, Pawson T. The UNC-73/Trio RhoGEF-2 domain is required in separate isoforms for the regulation of pharynx pumping and normal neurotransmission in C. elegans. Genes Dev 2005; 19:2016-29. [PMID: 16140983 PMCID: PMC1199572 DOI: 10.1101/gad.1319905] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Accepted: 07/06/2005] [Indexed: 11/24/2022]
Abstract
In both Caenorhabditis elegans and Drosophila, UNC-73/Trio functions in axon guidance by signaling through the Rac GTPase to regulate cytoskeletal rearrangements necessary for growth cone migrations. Here, we show that the complex C. elegans unc-73 gene encodes at least eight differentially expressed UNC-73 intracellular protein isoforms. Previously reported mutations affecting UNC-73 isoforms encoding the Rac-specific RhoGEF-1 domain cause uncoordinated movement, correlating with defects in axon guidance. Mutations in isoforms encoding the Rho-specific RhoGEF-2 domain, which we describe here, result in L1 stage larval lethality with no associated axon guidance defects. Isoform-specific rescue experiments reveal separate functions for the various RhoGEF-2-containing UNC-73 isoforms, which would not likely be discovered by conventional genetic screening. UNC-73 D1 and D2 appear to function redundantly in pharynx muscle to regulate the rate and strength of pharynx pumping, and in the HSN neurons and vulval muscles to control egg laying. Isoforms C1, C2, E, and F act redundantly within the nervous system to regulate the speed of locomotion. The multiple UNC-73 isoforms containing Rac- and Rho-specific RhoGEF domains therefore have distinct physiological functions. In addition to its previously identified role involving RhoGEF-1 in migrating cells and growth cones, our data indicate that UNC-73 signals through RhoGEF-2 to regulate pharynx and vulva musculature and to modulate synaptic neurotransmission.
Collapse
Affiliation(s)
- Robert Steven
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
| | | | | | | |
Collapse
|
292
|
Choi J, Ko J, Racz B, Burette A, Lee JR, Kim S, Na M, Lee HW, Kim K, Weinberg RJ, Kim E. Regulation of dendritic spine morphogenesis by insulin receptor substrate 53, a downstream effector of Rac1 and Cdc42 small GTPases. J Neurosci 2005; 25:869-79. [PMID: 15673667 PMCID: PMC6725612 DOI: 10.1523/jneurosci.3212-04.2005] [Citation(s) in RCA: 168] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The small GTPases Rac1 and Cdc42 are key regulators of the morphogenesis of actin-rich dendritic spines in neurons. However, little is known about how activated Rac1/Cdc42 regulates dendritic spines. Insulin receptor substrate 53 (IRSp53), which is highly expressed in the postsynaptic density (PSD), is known to link activated Rac1/Cdc42 to downstream effectors for actin regulation in non-neural cells. Here, we report that IRSp53 interacts with two specific members of the PSD-95 family, PSD-95 and chapsyn-110/PSD-93, in brain. An IRSp53 mutant lacking the C-terminal PSD-95-binding motif shows significant loss of synaptic localization in cultured neurons. Overexpression of IRSp53 in cultured neurons increases the density of dendritic spines but does not affect their length or width. Conversely, short-interfering RNA-mediated knock-down of IRSp53 reduces the density, length, and width of spines. In addition, the density and size of spines are decreased by a dominant-negative IRSp53 with a point mutation in the Src homology 3 (SH3) domain and a dominant-negative proline-rich region of WAVE2 (Wiskott-Aldrich syndrome protein family Verprolin-homologous protein), a downstream effector of IRSp53 that binds to the SH3 domain of IRSp53. These results suggest that PSD-95 interaction is an important determinant of synaptic IRSp53 localization and that the SH3 domain of IRSp53 links activated Rac1/Cdc42 to downstream effectors for the regulation of spine morphogenesis.
Collapse
Affiliation(s)
- Jeonghoon Choi
- National Creative Research Initiative Center for Synaptogenesis and Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
293
|
Newey SE, Velamoor V, Govek EE, Van Aelst L. Rho GTPases, dendritic structure, and mental retardation. ACTA ACUST UNITED AC 2005; 64:58-74. [PMID: 15884002 DOI: 10.1002/neu.20153] [Citation(s) in RCA: 276] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A consistent feature of neurons in patients with mental retardation is abnormal dendritic structure and/or alterations in dendritic spine morphology. Deficits in the regulation of the dendritic cytoskeleton affect both the structure and function of dendrites and synapses and are believed to underlie mental retardation in some instances. In support of this, there is good evidence that alterations in signaling pathways involving the Rho family of small GTPases, key regulators of the actin and microtubule cytoskeletons, contribute to both syndromic and nonsyndromic mental retardation disorders. Because the Rho GTPases have been shown to play increasingly well-defined roles in determining dendrite and dendritic spine development and morphology, Rho signaling has been suggested to be important for normal cognition. The purpose of this review is to summarize recent data on the Rho GTPases pertaining to dendrite and dendritic spine morphogenesis, as well as to highlight their involvement in mental retardation resulting from a variety of genetic mutations within regulators and effectors of these molecules.
Collapse
|
294
|
Chakrabarti K, Lin R, Schiller NI, Wang Y, Koubi D, Fan YX, Rudkin BB, Johnson GR, Schiller MR. Critical role for Kalirin in nerve growth factor signaling through TrkA. Mol Cell Biol 2005; 25:5106-18. [PMID: 15923627 PMCID: PMC1140581 DOI: 10.1128/mcb.25.12.5106-5118.2005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Kalirin is a multidomain guanine nucleotide exchange factor (GEF) that activates Rho proteins, inducing cytoskeletal rearrangement in neurons. Although much is known about the effects of Kalirin on Rho GTPases and neuronal morphology, little is known about the association of Kalirin with the receptor/signaling systems that affect neuronal morphology. Our experiments demonstrate that Kalirin binds to and colocalizes with the TrkA neurotrophin receptor in neurons. In PC12 cells, inhibition of Kalirin expression using antisense RNA decreased nerve growth factor (NGF)-induced TrkA autophosphorylation and process extension. Kalirin overexpression potentiated neurotrophin-stimulated TrkA autophosphorylation and neurite outgrowth in PC12 cells at a low concentration of NGF. Furthermore, elevated Kalirin expression resulted in catalytic activation of TrkA, as demonstrated by in vitro kinase assays and increased NGF-stimulated cellular activation of Rac, Mek, and CREB. Domain mapping demonstrated that the N-terminal Kalirin pleckstrin homology domain mediates the interaction with TrkA. The effects of Kalirin on TrkA provide a molecular basis for the requirement of Kalirin in process extension from PC12 cells and for previously observed effects on axonal extension and dendritic maintenance. The interaction of TrkA with the pleckstrin homology domain of Kalirin may be one example of a general mechanism whereby receptor/Rho GEF pairings play an important role in receptor tyrosine kinase activation and signal transduction.
Collapse
Affiliation(s)
- Kausik Chakrabarti
- University of Connecticut Health Center, Department of Neuroscience, 263 Farmington Ave., Farmington, CT 06030-4301, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
295
|
Boda B, Alberi S, Nikonenko I, Node-Langlois R, Jourdain P, Moosmayer M, Parisi-Jourdain L, Muller D. The mental retardation protein PAK3 contributes to synapse formation and plasticity in hippocampus. J Neurosci 2005; 24:10816-25. [PMID: 15574732 PMCID: PMC6730202 DOI: 10.1523/jneurosci.2931-04.2004] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mutations of the gene coding for PAK3 (p21-activated kinase 3) are associated with X-linked, nonsyndromic forms of mental retardation (MRX) in which the only distinctive clinical feature is the cognitive deficit. The mechanisms through which PAK3 mutation produces the mental handicap remain unclear, although an involvement in the mechanisms that regulate the formation or plasticity of synaptic networks has been proposed. Here we show, using a transient transfection approach, that antisense and small interfering RNA-mediated suppression of PAK3 or expression of a dominant-negative PAK3 carrying the human MRX30 mutation in rat hippocampal organotypic slice cultures results in the formation of abnormally elongated dendritic spines and filopodia-like protrusions and a decrease in mature spine synapses. Ultrastructural analysis of the changes induced by expression of PAK3 carrying the MRX30 mutation reveals that many elongated spines fail to express postsynaptic densities or contact presynaptic terminals. These defects are associated with a reduced spontaneous activity, altered expression of AMPA-type glutamate receptors, and defective long-term potentiation. Together, these data identify PAK3 as a key regulator of synapse formation and plasticity in the hippocampus and support interpretations that these defects might contribute to the cognitive deficits underlying this form of mental retardation.
Collapse
MESH Headings
- Amino Acid Substitution
- Animals
- Biolistics
- Cell Line, Tumor/ultrastructure
- Codon, Nonsense
- Cognition Disorders/genetics
- Cognition Disorders/physiopathology
- Dendrites/ultrastructure
- Genes, Dominant
- Hippocampus/drug effects
- Hippocampus/metabolism
- Hippocampus/ultrastructure
- Humans
- Long-Term Potentiation
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/physiopathology
- Mental Retardation, X-Linked/psychology
- Mice
- Morphogenesis
- Mutation, Missense
- NIH 3T3 Cells
- Neuroblastoma/pathology
- Organ Culture Techniques
- Protein Serine-Threonine Kinases/chemistry
- Protein Serine-Threonine Kinases/deficiency
- Protein Serine-Threonine Kinases/genetics
- Protein Serine-Threonine Kinases/physiology
- Protein Structure, Tertiary
- Pseudopodia/ultrastructure
- Pyramidal Cells/physiology
- RNA, Antisense/pharmacology
- RNA, Antisense/toxicity
- RNA, Small Interfering/pharmacology
- RNA, Small Interfering/toxicity
- Rats
- Receptors, AMPA/deficiency
- Recombinant Fusion Proteins/physiology
- Transfection
- p21-Activated Kinases
Collapse
Affiliation(s)
- Bernadett Boda
- Department of Basic Neuroscience, Centre Medical Universitaire, 1211 Geneva 4, Switzerland
| | | | | | | | | | | | | | | |
Collapse
|
296
|
Abstract
Eph receptor tyrosine kinases mould the behaviour of many cell types by binding membrane-anchored ligands, ephrins, at sites of cell-cell contact. Eph signals affect both of the contacting cells and can produce diverse biological responses. New models explain how quantitative variations in the densities and signalling abilities of Eph receptors and ephrins could account for the different effects that are elicited on axon guidance, cell adhesion and cell migration during development, homeostasis and disease.
Collapse
Affiliation(s)
- Elena B Pasquale
- The Burnham Institute, 10901 N. Torrey Pines Road, La Jolla, California 92037, USA.
| |
Collapse
|
297
|
Schiller MR, Blangy A, Huang J, Mains RE, Eipper BA. Induction of lamellipodia by Kalirin does not require its guanine nucleotide exchange factor activity. Exp Cell Res 2005; 307:402-17. [PMID: 15950621 DOI: 10.1016/j.yexcr.2005.03.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Revised: 03/18/2005] [Accepted: 03/18/2005] [Indexed: 11/26/2022]
Abstract
Guanine nucleotide exchange factor (GEF) domains of the Dbl family occur in a variety of proteins that include multiple protein-protein and protein-lipid interaction domains. We used an epithelial-derived cell line to investigate the mechanisms by which the two GEF domains of Kalirin, a neuronal Rho GEF, influence morphology. As expected, Kal-GEF1, an efficient GEF for Rac1 and RhoG, induced the formation of lamellipodia resembling those induced by active Rac1. Although Kal-GEF1 activated Rac and Pak, its ability to induce formation of lamellipodia was not blocked by dominant negative Rho GTPases or by catalytically inactive Pak. Consistent with this, a catalytically inactive mutant of Kal-GEF1 induced formation of lamellipodia and activated Pak. Active Pak was required for the GEF-activity independent effect of Kal-GEF1 and the lamellipodia produced were filled with ribs of filamentous actin. Kal-GEF1 and a GEF-dead mutant co-immunoprecipitated with Pak. The interaction of Kal-GEF1 with Pak is indirect and requires the regulatory protein binding domain of Pak. Filamin A, which is known to interact with and activate Pak, binds to both catalytically active and inactive Kal-GEF1, providing a link by which catalytically inactive Kal-GEF1 can activate Pak and induce lamellipodia. Together, our results indicate that Kal-GEF1 induces lamellipodia through activation of Pak, where GEF activity is not required. GEF-activity-independent effects on downstream targets may be a general property of RhoGEFs.
Collapse
Affiliation(s)
- Martin R Schiller
- Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030-3401, USA.
| | | | | | | | | |
Collapse
|
298
|
|
299
|
Kennedy MB, Beale HC, Carlisle HJ, Washburn LR. Integration of biochemical signalling in spines. Nat Rev Neurosci 2005; 6:423-34. [PMID: 15928715 DOI: 10.1038/nrn1685] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Short-term and long-term changes in the strength of synapses in neural networks underlie working memory and long-term memory storage in the brain. These changes are regulated by many biochemical signalling pathways in the postsynaptic spines of excitatory synapses. Recent findings about the roles and regulation of the small GTPases Ras, Rap and Rac in spines provide new insights into the coordination and cooperation of different pathways to effect synaptic plasticity. Here, we present an initial working representation of the interactions of five signalling cascades that are usually studied individually. We discuss their integrated function in the regulation of postsynaptic plasticity.
Collapse
Affiliation(s)
- Mary B Kennedy
- Division of Biology 216-76, California Institute of Technology, Pasadena, California 91125, USA.
| | | | | | | |
Collapse
|
300
|
Abstract
Many forms of mental retardation and cognitive disability are associated with abnormalities in dendritic spine morphology. Visualization of spines using live-imaging techniques provides convincing evidence that spine morphology is altered in response to certain forms of LTP-inducing stimulation. Thus, information storage at the cellular level appears to involve changes in spine morphology that support changes in synaptic strength produced by certain patterns of synaptic activity. Because the structure of a spine is determined by its underlying actin cytoskeleton, there has been much effort to identify signaling pathways linking synaptic activity to control of actin polymerization. This review, part of the TINS Synaptic Connectivity series, discusses recent studies that implicate EphB and NMDA receptors in the regulation of actin-binding proteins through modulation of Rho family small GTPases.
Collapse
Affiliation(s)
- Holly J Carlisle
- California Institute of Technology, Division of Biology 216-76, Pasadena, CA 91125, USA
| | | |
Collapse
|