201
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Lindwall C, Fothergill T, Richards LJ. Commissure formation in the mammalian forebrain. Curr Opin Neurobiol 2007; 17:3-14. [PMID: 17275286 DOI: 10.1016/j.conb.2007.01.008] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Accepted: 01/18/2007] [Indexed: 01/06/2023]
Abstract
Commissural formation in the mammalian brain is highly organised and regulated both by the cell-autonomous expression of transcription factors, and by non-cell-autonomous mechanisms including the formation of midline glial structures and their expression of specific axon guidance molecules. These mechanisms channel axons into the correct path and enable the subsequent connection of specific brain areas to their appropriate targets. Several key findings have been made over the past two years, including the discovery of novel mechanisms of action that 'classical' guidance factors such as the Slits, Netrins, and their receptors have in axon guidance. Moreover, novel guidance factors such as members of the Wnt family, and extracellular matrix components such as heparan sulphate proteoglycans, have been shown to be important for mammalian brain commissure formation. Additionally, there have been significant discoveries regarding the role of FGF signalling in the formation of midline glial structures. In this review, we discuss the most recent advances in the field that have contributed to our current understanding of commissural development in the telencephalon.
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Affiliation(s)
- Charlotta Lindwall
- The University of Queensland, School of Biomedical Sciences and The Queensland Brain Institute, St Lucia, Queensland 4072, Australia
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202
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Hur EM, Kim KT. A role of local signalling in the establishment and maintenance of the asymmetrical architecture of a neuron. J Neurochem 2007; 101:600-10. [PMID: 17217410 DOI: 10.1111/j.1471-4159.2006.04372.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Significant progress has been made in the identification of intrinsic and extrinsic factors involved in the development of nervous system. It is remarkable that the establishment and maintenance of the asymmetrical architecture of a neuron is coordinated by a limited repertoire of signalling machineries. However, the details of signalling mechanisms responsible for creating specificity and diversity required for proper development of the nervous system remain largely to be investigated. An emerging body of evidence suggests that specificity and diversity can be achieved by differential regulation of signalling components at distinct subcellular localizations. Many aspects of neuronal polarization and morphogenesis are attributed to localized signalling. Further diversity and specificity of receptor signalling can be achieved by the regulation of molecules outside the cell. Recent evidence suggests that extracellular matrix molecules are essential extrinsic cues that function to foster the growth of neurons. Therefore, it is important to understand where the signalling machineries are activated and how they are combined with other factors in order to understand the molecular mechanism underlying neuronal development.
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Affiliation(s)
- Eun-Mi Hur
- Department of Life Science and Division of Molecular and Life Sciences, Systems Biodynamics NCRC, Pohang University of Science and Technology, Pohang, South Korea
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203
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Toyofuku T, Kikutani H. Semaphorin Signaling During Cardiac Development. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 600:109-17. [PMID: 17607950 DOI: 10.1007/978-0-387-70956-7_9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Toshihiko Toyofuku
- Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, Osaka, Japan
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204
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Evans IR, Renne T, Gertler FB, Nobes CD. Ena/VASP proteins mediate repulsion from ephrin ligands. J Cell Sci 2006; 120:289-98. [PMID: 17179204 DOI: 10.1242/jcs.03333] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Ena/VASP proteins negatively regulate cell motility and contribute to repulsion from several guidance cues; however, there is currently no evidence for a role downstream of Eph receptors. Eph receptors mediate repulsion from ephrins at sites of intercellular contact during several developmental migrations. For example, the expression of ephrin-Bs in posterior halves of somites restricts neural crest cell migration to the anterior halves. Here we show that ephrin-B2 destabilises neural crest cell lamellipodia when presented in a substrate-bound or soluble form. Our timelapse studies show that repulsive events are associated with the rearward collapse and subsequent loss of lamellipodia as membrane ruffles. We hypothesise that Ena/VASP proteins contribute to repulsion from ephrins by destabilising cellular protrusions and show that Ena/VASP-deficient fibroblasts exhibit reduced repulsion from both ephrin-A and ephrin-B stripes compared to wild-type controls. Moreover, when EphB4 and ephrin-B2 were expressed in neighbouring Swiss 3T3 fibroblasts, VASP and Mena co-accumulated with activated Eph receptors at protrusions formed by EphB4-expressing cells. Sequestration of Ena/VASP proteins away from the periphery of these cells inhibited Eph receptor internalisation, a process that facilitates repulsion. Our results suggest that Ena/VASP proteins regulate ephrin-induced Eph receptor signalling events, possibly by destabilising lamellipodial protrusions.
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Affiliation(s)
- Iwan R Evans
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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205
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Garbe DS, Das A, Dubreuil RR, Bashaw GJ. beta-Spectrin functions independently of Ankyrin to regulate the establishment and maintenance of axon connections in the Drosophila embryonic CNS. Development 2006; 134:273-84. [PMID: 17121810 DOI: 10.1242/dev.02653] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
alpha- and beta-Spectrin are major components of a submembrane cytoskeletal network connecting actin filaments to integral plasma membrane proteins. Besides its structural role in red blood cells, the Spectrin network is thought to function in non-erythroid cells during protein targeting and membrane domain formation. Here, we demonstrate that beta-Spectrin is required in neurons for proper midline axon guidance in the Drosophila embryonic CNS. In beta-spectrin mutants many axons inappropriately cross the CNS midline, suggesting a role for beta-Spectrin in midline repulsion. Surprisingly, neither the Ankyrin-binding nor the pleckstrin homology (PH) domains of beta-Spectrin are required for accurate guidance decisions. alpha-Spectrin is dependent upon beta-Spectrin for its normal subcellular localization and/or maintenance, whereas alpha-spectrin mutants exhibit a redistribution of beta-Spectrin to the axon scaffold. beta-spectrin mutants show specific dose-dependent genetic interactions with the midline repellent slit and its neuronal receptor roundabout (robo), but not with other guidance molecules. The results suggest that beta-Spectrin contributes to midline repulsion through the regulation of Slit-Robo pathway components. We propose that the Spectrin network is playing a role independently of Ankyrin in the establishment and/or maintenance of specialized membrane domains containing guidance molecules that ensure the fidelity of axon repulsion at the midline.
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Affiliation(s)
- David S Garbe
- Department of Neuroscience, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104, USA
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206
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Yang L, Bashaw GJ. Son of sevenless directly links the Robo receptor to rac activation to control axon repulsion at the midline. Neuron 2006; 52:595-607. [PMID: 17114045 DOI: 10.1016/j.neuron.2006.09.039] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Revised: 09/13/2006] [Accepted: 09/29/2006] [Indexed: 11/23/2022]
Abstract
Son of sevenless (Sos) is a dual specificity guanine nucleotide exchange factor (GEF) that regulates both Ras and Rho family GTPases and thus is uniquely poised to integrate signals that affect both gene expression and cytoskeletal reorganization. Here, using genetics, biochemistry, and cell biology, we demonstrate that Sos is recruited to the plasma membrane, where it forms a ternary complex with the Roundabout receptor and the SH3-SH2 adaptor protein Dreadlocks (Dock) to regulate Rac-dependent cytoskeletal rearrangement in response to the Slit ligand. Intriguingly, the Ras and Rac-GEF activities of Sos can be uncoupled during Robo-mediated axon repulsion; Sos axon guidance function depends on its Rac-GEF activity, but not its Ras-GEF activity. These results provide in vivo evidence that the Ras and RhoGEF domains of Sos are separable signaling modules and support a model in which Robo recruits Sos to the membrane via Dock to activate Rac during midline repulsion.
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MESH Headings
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/metabolism
- Animals
- Cell Communication/physiology
- Cell Line, Tumor
- Cell Membrane/metabolism
- Cues
- Cytoskeleton/genetics
- Cytoskeleton/metabolism
- Drosophila/cytology
- Drosophila/embryology
- Drosophila/metabolism
- Drosophila Proteins
- Gene Expression Regulation, Developmental/physiology
- Growth Cones/metabolism
- Growth Cones/ultrastructure
- Humans
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/metabolism
- Nervous System/cytology
- Nervous System/embryology
- Nervous System/metabolism
- Protein Structure, Tertiary/physiology
- Protein Transport/physiology
- Receptors, Immunologic/genetics
- Receptors, Immunologic/metabolism
- Signal Transduction/physiology
- Son of Sevenless Protein, Drosophila/chemistry
- Son of Sevenless Protein, Drosophila/genetics
- Son of Sevenless Protein, Drosophila/metabolism
- rac GTP-Binding Proteins/genetics
- rac GTP-Binding Proteins/metabolism
- Roundabout Proteins
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Affiliation(s)
- Long Yang
- Department of Neuroscience, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA
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207
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Joly W, Mugat B, Maschat F. Engrailed controls the organization of the ventral nerve cord through frazzled regulation. Dev Biol 2006; 301:542-54. [PMID: 17126316 DOI: 10.1016/j.ydbio.2006.10.019] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2005] [Revised: 09/20/2006] [Accepted: 10/14/2006] [Indexed: 11/19/2022]
Abstract
In Drosophila, the ventral nerve cord (VNC) architecture is built from neuroblasts that are specified during embryonic development, mainly by transcription factors. Here we show that Engrailed, a homeodomain transcription factor known to be involved in the establishment of neuroblast identity, is also directly implicated in the regulation of axonal guidance cues. Posterior commissures (PC) are missing in engrailed mutant embryos, and axonal pathfinding defects are observed when Engrailed is ectopically expressed at early stages, prior to neuronal specification. We also show that frazzled, enabled, and trio, all of which are potential direct targets of Engrailed and are involved in axonal navigation, interact genetically with engrailed to form posterior commissures in the developing VNC. The regulation of frazzled expression in engrailed-expressing neuroblasts contributes significantly to the formation of the posterior commissures by acting on axon growth. Finally, we identified a small genomic fragment within intron 1 of frazzled that can mediate activation by Engrailed in vivo when fused to a GFP reporter. These results indicate that Engrailed's function during the segregation of the neuroblasts is crucial for regulating different actors that are later involved in axon guidance.
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Affiliation(s)
- Willy Joly
- Institute of Human Genetics, IGH, UPR 1142, 141 rue de la Cardonille, 34396 Montpellier Cedex 5, France
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208
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Li X, Chen Y, Liu Y, Gao J, Gao F, Bartlam M, Wu JY, Rao Z. Structural basis of Robo proline-rich motif recognition by the srGAP1 Src homology 3 domain in the Slit-Robo signaling pathway. J Biol Chem 2006; 281:28430-7. [PMID: 16857672 PMCID: PMC2031215 DOI: 10.1074/jbc.m604135200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Slit-Robo (sr) GTPase-activating protein (GAPs) are important components in the intracellular pathway mediating Slit-Robo signaling in axon guidance and cell migration. We report the first crystal structure of the srGAP1 SH3 domain at 1.8-A resolution. The unusual side chain conformation of the conserved Phe-13 in the P1 pocket renders the ligand binding pocket shallow and narrow, which contributes toward the low binding affinity. Moreover, the opposing electrostatic charge and the hydrophobic properties of the P3 specificity pocket are consistent with the observed binding characteristics of the srGAP1 SH3 domain to its ligand. Surface plasmon resonance experiments indicate that the srGAP1 SH3 domain interacts with its natural ligand inaCtoN orientation. The srGAP1 SH3 domain can bind to both the CC2 and CC3 motifs in vitro. The N-terminal two acidic residues in the CC3 motif recognition site are necessary for srGAP1 SH3 domain binding. A longer CC3 peptide (CC3-FL) binds with greater affinity than its shorter counterpart, suggesting that the residues surrounding the proline-rich core are important for protein-peptide interactions. Our study reveals previously unknown properties of the srGAP-Robo interaction. Our data provide a structural basis for the srGAP-Robo interaction, consistent with the role of the Robo intracellular domain in interacting with other downstream signaling molecules and mediating versatile and dynamic responses to axon guidance and cell migration cues.
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Affiliation(s)
- Xiaofeng Li
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
- National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China
| | - Yushu Chen
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
- National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China
| | - Yiwei Liu
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
| | - Jia Gao
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
| | - Feng Gao
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
| | - Mark Bartlam
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
- National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China
| | - Jane Y. Wu
- National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China
- Department of Neurology; Center of Genetic Medicine, Lurie Cancer Center; Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Zihe Rao
- “Tsinghua-IBP Joint Research Group for Structural Biology”, Tsinghua University, Beijing 100084, China
- National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China
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209
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Abstract
Sprouty-related proteins with an EVH1 domain (Spreds) belong to a new protein family harboring a conserved N-terminal EVH1 domain, which is related to the VASP (vasodilator-stimulated phosphoprotein) EVH1 domain (Enabled/VASP homology 1 domain) and a C-terminal Sprouty-related domain, typical for Sprouty proteins. Spreds were, like Sproutys, initially discovered as inhibitors of the Ras/MAPK pathway, and the SPR (Sprouty-related) domains of both protein families seem to be very important for many protein interactions and cellular processes. VASP was initially characterized as a proline-rich substrate of protein kinases A and G in human platelets and later shown to be a scaffold protein, regulating both signal transduction pathways and the actin filament system. The VASP-EVH1 domain is known to bind specifically to a FP(4) binding motif, which is, for example, present in the focal adhesion proteins vinculin and zyxin. In this review we give a structural and functional overview on these three protein families and ask whether nature plays a modular protein domain puzzle with stable exchangeable elements or if these closely related domains have various functions when pasted in a different protein context.
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Affiliation(s)
- Karin Bundschu
- Abteilung Biochemie und Molekulare Biologie, Universität Ulm, 89081 Ulm, Germany.
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210
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Werbowetski-Ogilvie TE, Seyed Sadr M, Jabado N, Angers-Loustau A, Agar NYR, Wu J, Bjerkvig R, Antel JP, Faury D, Rao Y, Del Maestro RF. Inhibition of medulloblastoma cell invasion by Slit. Oncogene 2006; 25:5103-12. [PMID: 16636676 PMCID: PMC2072874 DOI: 10.1038/sj.onc.1209524] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 01/27/2006] [Accepted: 02/22/2006] [Indexed: 11/09/2022]
Abstract
Invasion of brain tumor cells has made primary malignant brain neoplasms among the most recalcitrant to therapeutic strategies. We tested whether the secreted protein Slit2, which guides the projection of axons and developing neurons, could modulate brain tumor cell invasion. Slit2 inhibited the invasion of medulloblastoma cells in a variety of in vitro models. The effect of Slit2 was inhibited by the Robo ectodomain. Time-lapse videomicroscopy indicated that Slit2 reduced medulloblastoma invasion rate without affecting cell direction or proliferation. Both medulloblastoma and glioma tumors express Robo1 and Slit2, but only medulloblastoma invasion is inhibited by recombinant Slit2 protein. Downregulation of activated Cdc42 may contribute to this differential response. Our findings reinforce the concept that neurodevelopmental cues such as Slit2 may provide insights into brain tumor invasion.
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Affiliation(s)
- T E Werbowetski-Ogilvie
- Brain Tumour Research Centre, Montreal Neurological Institute, McGill University, Montreal, QC, Canada
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211
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Hohenester E, Hussain S, Howitt JA. Interaction of the guidance molecule Slit with cellular receptors. Biochem Soc Trans 2006; 34:418-21. [PMID: 16709176 DOI: 10.1042/bst0340418] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Slits are large secreted glycoproteins characterized by an unusual tandem of four LRR (leucine-rich repeat) domains in their N-terminal half. Slit proteins were initially described as repulsive guidance cues in neural development, but it has become clear that they have additional important functions, for instance in the vasculature and immune system. Genetic studies have identified two types of cellular receptors for Slits: Robos (Roundabout) and the HS (heparan sulphate) proteoglycan syndecan. The intracellular signalling cascade downstream of Robo activation is slowly being elucidated, but the mechanism of transmembrane signalling by Robo has remained obscure. No active signalling role for syndecan has yet been demonstrated. Slit-HS interactions may be important for shaping the presumed Slit gradient or presenting Slit at its target cell surface. Recent studies have mapped the binding sites for Robos and HS/heparin to discrete Slit domains. Robos bind to the second LRR domain of Slit, whereas HS/heparin binds with very high affinity to the C-terminal portion of Slit. Slit activity is likely to be modulated by physiological proteolytic cleavage in the region separating the Robo and HS/heparin-binding sites.
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Affiliation(s)
- E Hohenester
- Division of Cell and Molecular Biology, Imperial College London, South Kensington Campus, UK
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212
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Murray MJ, Davidson CM, Hayward NM, Brand AH. The Fes/Fer non-receptor tyrosine kinase cooperates with Src42A to regulate dorsal closure in Drosophila. Development 2006; 133:3063-73. [PMID: 16831834 DOI: 10.1242/dev.02467] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Fes/Fer non-receptor tyrosine kinases regulate cell adhesion and cytoskeletal reorganisation through the modification of adherens junctions. Unregulated Fes/Fer kinase activity has been shown to lead to tumours in vivo. Here, we show that Drosophila Fer localises to adherens junctions in the dorsal epidermis and regulates a major morphological event, dorsal closure. Mutations in Src42A cause defects in dorsal closure similar to those seen in dfer mutant embryos. Furthermore, Src42A mutations enhance the dfer mutant phenotype, suggesting that Src42A and DFer act in the same cellular process. We show that DFer is required for the formation of the actin cable in leading edge cells and for normal rates of dorsal closure. We have isolated a gain-of-function mutation in dfer (dfergof) that expresses an N-terminally fused form of the protein, similar to oncogenic forms of vertebrate Fer. dfergof blocks dorsal closure and causes axon misrouting. We find that in dfer loss-of-function mutants beta-catenin is hypophosphorylated, whereas in dfergof beta-catenin is hyperphosphorylated. Phosphorylated beta-catenin is removed from adherens junctions and degraded, thus implicating DFer in the regulation of adherens junctions.
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Affiliation(s)
- Michael J Murray
- The Gurdon Institute and Department of Physiology, Development and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
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213
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Chang C, Adler CE, Krause M, Clark SG, Gertler FB, Tessier-Lavigne M, Bargmann CI. MIG-10/lamellipodin and AGE-1/PI3K promote axon guidance and outgrowth in response to slit and netrin. Curr Biol 2006; 16:854-62. [PMID: 16618541 DOI: 10.1016/j.cub.2006.03.083] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2005] [Revised: 03/19/2006] [Accepted: 03/24/2006] [Indexed: 12/27/2022]
Abstract
BACKGROUND The cytoplasmic C. elegans protein MIG-10 affects cell migrations and is related to mammalian proteins that bind phospholipids and Ena/VASP actin regulators. In cultured cells, mammalian MIG-10 promotes lamellipodial growth and Ena/VASP proteins induce filopodia. RESULTS We show here that during neuronal development, mig-10 and the C. elegans Ena/VASP homolog unc-34 cooperate to guide axons toward UNC-6 (netrin) and away from SLT-1 (Slit). The single mutants have relatively mild phenotypes, but mig-10; unc-34 double mutants arrest early in development with severe axon guidance defects. In axons that are guided toward ventral netrin, unc-34 is required for the formation of filopodia and mig-10 increases the number of filopodia. In unc-34 mutants, developing axons that lack filopodia are still guided to netrin through lamellipodial growth. In addition to its role in axon guidance, mig-10 stimulates netrin-dependent axon outgrowth in a process that requires the age-1 phosphoinositide-3 lipid kinase but not unc-34. CONCLUSIONS mig-10 and unc-34 organize intracellular responses to both attractive and repulsive axon guidance cues. mig-10 and age-1 lipid signaling promote axon outgrowth; unc-34 and to a lesser extent mig-10 promote filopodia formation. Surprisingly, filopodia are largely dispensable for accurate axon guidance.
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Affiliation(s)
- Chieh Chang
- Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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214
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Quinn CC, Pfeil DS, Chen E, Stovall EL, Harden MV, Gavin MK, Forrester WC, Ryder EF, Soto MC, Wadsworth WG. UNC-6/netrin and SLT-1/slit guidance cues orient axon outgrowth mediated by MIG-10/RIAM/lamellipodin. Curr Biol 2006; 16:845-53. [PMID: 16563765 DOI: 10.1016/j.cub.2006.03.025] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2005] [Revised: 03/09/2006] [Accepted: 03/10/2006] [Indexed: 12/30/2022]
Abstract
BACKGROUND Axon migrations are guided by extracellular cues that can act as repellants or attractants. However, the logic underlying the manner through which attractive and repulsive responses are determined is unclear. Many extracellular guidance cues, and the cellular components that mediate their signals, have been implicated in both types of responses. RESULTS Genetic analyses indicate that MIG-10/RIAM/lamellipodin, a cytoplasmic adaptor protein, functions downstream of the attractive guidance cue UNC-6/netrin and the repulsive guidance cue SLT-1/slit to direct the ventral migration of the AVM and PVM axons in C. elegans. Furthermore, overexpression of MIG-10 in the absence of UNC-6 and SLT-1 induces a multipolar phenotype with undirected outgrowths. Addition of either UNC-6 or SLT-1 causes the neurons to become monopolar. Moreover, the ability of UNC-6 or SLT-1 to direct the axon ventrally is enhanced by the MIG-10 overexpression. We also demonstrate that an interaction between MIG-10 and UNC-34, a protein that promotes actin-filament extension, is important in the response to guidance cues and that MIG-10 colocalizes with actin in cultured cells, where it can induce the formation of lamellipodia. CONCLUSIONS We conclude that MIG-10 mediates the guidance of AVM and PVM axons in response to the extracellular UNC-6 and SLT-1 guidance cues. The attractive and repulsive guidance cues orient MIG-10-dependant axon outgrowth to cause a directional response.
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Affiliation(s)
- Christopher C Quinn
- Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
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215
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Zhang Y, Tu Y, Gkretsi V, Wu C. Migfilin interacts with vasodilator-stimulated phosphoprotein (VASP) and regulates VASP localization to cell-matrix adhesions and migration. J Biol Chem 2006; 281:12397-407. [PMID: 16531412 DOI: 10.1074/jbc.m512107200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cell migration is a complex process that is coordinately regulated by cell-matrix adhesion and actin cytoskeleton. We report here that migfilin, a recently identified component of cell-matrix adhesions, is a biphasic regulator of cell migration. Loss of migfilin impairs cell migration. Surprisingly, overexpression of migfilin also reduces cell migration. Molecularly, we have identified vasodilator-stimulated phosphoprotein (VASP) as a new migfilin-binding protein. The interaction is mediated by the VASP EVH1 domain and a single L104PPPPP site located within the migfilin proline-rich domain. Migfilin and VASP form a complex in both suspended and adhered cells, and in the latter, they co-localize in cell-matrix adhesions. Functionally, migfilin facilitates VASP localization to cell-matrix adhesions. Using two different approaches (VASP-binding defective migfilin mutants and small interfering RNA-mediated VASP knockdown), we show that the interaction with VASP is crucially involved in migfilin-mediated regulation of cell migration. Our results identify migfilin as an important regulator of cell migration and provide new information on the mechanism by which migfilin regulates this process.
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Affiliation(s)
- Yongjun Zhang
- Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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216
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217
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Strickland P, Shin GC, Plump A, Tessier-Lavigne M, Hinck L. Slit2 and netrin 1 act synergistically as adhesive cues to generate tubular bi-layers during ductal morphogenesis. Development 2006; 133:823-32. [PMID: 16439476 DOI: 10.1242/dev.02261] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Development of many organs, including the mammary gland, involves ductal morphogenesis. Mammary ducts are bi-layered tubular structures comprising an outer layer of cap/myoepithelial cells (MECs) and an inner layer of luminal epithelial cells (LECs). Slit2 is expressed by cells in both layers, with secreted SLIT2 broadly distributed throughout the epithelial compartment. By contrast, Robo1 is expressed specifically by cap/MECs. Loss-of-function mutations in Slit2 and Robo1 yield similar phenotypes, characterized by disorganized end buds (EBs) reminiscent of those present in Ntn1(-/-) glands, suggesting that SLIT2 and NTN1 function in concert during mammary development. Analysis of Slit2(-/-);Ntn1(-/-) glands demonstrates an enhanced phenotype that extends through the ducts and is characterized by separated cell layers and occluded lumens. Aggregation assays show that Slit2(-/-);Ntn1(-/-) cells, in contrast to wild-type cells, do not form bi-layered organoids, a defect rescued by addition of SLIT2. NTN1 has no effect alone, but synergistically enhances this rescue. Thus, our data establish a novel role for SLIT2 as an adhesive cue, acting in parallel with NTN1 to generate cell boundaries along ducts during bi-layered tube formation.
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Affiliation(s)
- Phyllis Strickland
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, 95064, USA
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218
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Moresco EMY, Donaldson S, Williamson A, Koleske AJ. Integrin-mediated dendrite branch maintenance requires Abelson (Abl) family kinases. J Neurosci 2006; 25:6105-18. [PMID: 15987940 PMCID: PMC6725048 DOI: 10.1523/jneurosci.1432-05.2005] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Dendrite arbor structure is a critical determinant of nervous system function that must be actively maintained throughout life, but the signaling pathways that regulate dendrite maintenance are essentially unknown. We report that the Abelson (Abl) and Abl-related gene (Arg) nonreceptor tyrosine kinases are required for maintenance of cortical dendrites in the mouse brain. arg-/- cortical dendrites initially develop normally and are indistinguishable from wild-type dendrites at postnatal day 21. Dendrite branches are not efficiently maintained in arg-/- neurons, leading to a reduction in dendrite arbor size by early adulthood. More severe dendrite loss is observed in abl-/-arg-/- neurons. Elevation of Arg kinase activity in primary cortical neurons promotes axon and dendrite branching. Activation of integrin receptors by adhesion to laminin-1 or Semaphorin 7A also promotes neurite branching in cortical neurons, but this response is absent in arg-/- neurons because of the reduced dynamic behavior of mutant neurite branches. These data suggest that integrin signaling through Abl and Arg support cortical dendrite branch maintenance by promoting dendrite branch dynamics in response to adhesive cues.
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Affiliation(s)
- Eva Marie Yang Moresco
- Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06520-8024, USA
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219
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Piper M, Anderson R, Dwivedy A, Weinl C, van Horck F, Leung KM, Cogill E, Holt C. Signaling mechanisms underlying Slit2-induced collapse of Xenopus retinal growth cones. Neuron 2006; 49:215-28. [PMID: 16423696 PMCID: PMC3689199 DOI: 10.1016/j.neuron.2005.12.008] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Revised: 09/23/2005] [Accepted: 12/05/2005] [Indexed: 10/25/2022]
Abstract
Slits mediate multiple axon guidance decisions, but the mechanisms underlying the responses of growth cones to these cues remain poorly defined. We show here that collapse induced by Slit2-conditioned medium (Slit2-CM) in Xenopus retinal growth cones requires local protein synthesis (PS) and endocytosis. Slit2-CM elicits rapid activation of translation regulators and MAP kinases in growth cones, and inhibition of MAPKs or disruption of heparan sulfate blocks Slit2-CM-induced PS and repulsion. Interestingly, Slit2-CM causes a fast PS-dependent decrease in cytoskeletal F-actin concomitant with a PS-dependent increase in the actin-depolymerizing protein cofilin. Our findings reveal an unexpected link between Slit2 and cofilin in growth cones and suggest that local translation of actin regulatory proteins contributes to repulsion.
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Affiliation(s)
- Michael Piper
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Richard Anderson
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Asha Dwivedy
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Christine Weinl
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Francis van Horck
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Kin Mei Leung
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Emily Cogill
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
| | - Christine Holt
- Department of Physiology, Development and Neuroscience University of Cambridge Downing Street Cambridge United Kingdom
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220
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Li W, Li Y, Gao FB. Abelson, enabled, and p120 catenin exert distinct effects on dendritic morphogenesis in Drosophila. Dev Dyn 2006; 234:512-22. [PMID: 16003769 DOI: 10.1002/dvdy.20496] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Neurons exhibit diverse dendritic branching patterns that are important for their function. However, the signaling pathways that control the formation of different dendritic structures remain largely unknown. To address this issue in vivo, we use the peripheral nervous system (PNS) of Drosophila as a model system. Through both loss-of-function and gain-of-function analyses in vivo, we show here that the nonreceptor tyrosine kinase Abelson (Abl), an important regulator of cytoskeleton dynamics, inhibits dendritic branching of dendritic arborization (DA) sensory neurons in Drosophila. Enabled (Ena), a substrate for Abl, promotes the formation of both dendritic branches and actin-rich spine-like protrusions of DA neurons, an effect opposite to that of Abl. In contrast, p120 catenin (p120 ctn) primarily enhances the development of spine-like protrusions. These results suggest that Ena is a key regulator of dendritic branching and that different regulators of the actin cytoskeleton exert distinct effects on dendritic morphogenesis.
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Affiliation(s)
- Wenjun Li
- Gladstone Institute of Neurological Disease, San Francisco, California, USA
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221
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Hiramoto M, Hiromi Y. ROBO directs axon crossing of segmental boundaries by suppressing responsiveness to relocalized Netrin. Nat Neurosci 2006; 9:58-66. [PMID: 16341212 DOI: 10.1038/nn1612] [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] [Received: 09/15/2005] [Accepted: 11/09/2005] [Indexed: 11/09/2022]
Abstract
Networks in the CNS consist of neural modules that are connected in a repetitive array. Whereas individual modules contain guidance information along which axons track within the unit, these guidance cues hinder axon extension across module boundaries. We investigated how axons solve this 'boundary problem' by analyzing the longitudinal connections of neuromeres in Drosophila melanogaster. The initial trajectory of the longitudinal axons is guided by Netrin, which is localized on commissural axons by its receptor, Frazzled. The Netrin cue on the commissure of the next segment can act as a barrier to longitudinal axons, inhibiting their extension and misguiding them contralaterally along the commissure. We show that, before reaching the segmental boundary, the longitudinal axons' responsiveness to Netrin presented on the commissure is suppressed by Roundabout (ROBO), through counteracting Gq signaling. The absence of suppression causes the robo phenotype: longitudinal axons project toward the midline, as if running around a roundabout (rotary).
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Affiliation(s)
- Masaki Hiramoto
- Department of Developmental Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan.
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222
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Abstract
Commissural axons grow along complex pathways toward, across, and beyond the midline of the central nervous system. Taking commissural axons in the vertebrate spinal cord and the Drosophila ventral nerve cord as examples, we examine how commissural axon pathfinding is regulated by the Slit family of guidance cues and their Robo family receptors. We extract several principles that seem likely to apply to other axons and other contexts, such as the reiterative use of the same guidance molecules in distinct pathfinding decisions, the transcriptional specification of a pathway, the posttranscriptional regulation of growth along the pathway, and the possible role of feedback mechanisms to ensure the fidelity of pathfinding choices. Such mechanisms may help explain how a relatively small number of guidance molecules can generate complex and stereotyped wiring patterns. We also highlight the many gaps in our understanding of commissural axon pathfinding and question some widely accepted views. We hope that this review encourages further efforts to tackle these questions, in the expectation that this system will continue to reveal the general principles of axon pathfinding.
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Affiliation(s)
- Barry J Dickson
- Research Institute of Molecular Pathology (IMP), A-1030 Vienna, Austria.
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223
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Lilien J, Balsamo J. The regulation of cadherin-mediated adhesion by tyrosine phosphorylation/dephosphorylation of beta-catenin. Curr Opin Cell Biol 2005; 17:459-65. [PMID: 16099633 DOI: 10.1016/j.ceb.2005.08.009] [Citation(s) in RCA: 378] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Accepted: 08/03/2005] [Indexed: 11/18/2022]
Abstract
The formation of stable cell-cell adhesions by type I cadherins depends on the association of their cytoplasmic domain with beta-catenin, and of beta-catenin with alpha-catenin. The binding of beta-catenin to these partners is regulated by phosphorylation of at least three critical tyrosine residues. Each of these residues is targeted by one or more specific kinases: Y142 by Fyn, Fer and cMet; Y489 by Abl; and Y654 by Src and the epidermal growth factor receptor. Developmental and physiological signals have been identified that initiate the specific phosphorylation and dephosphorylation of these residues, regulating cadherin function during neurite outgrowth, permeability of airway epithelium and synapse remodeling, and possibly initiating epithelial cell migration during development and metastasis.
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Affiliation(s)
- Jack Lilien
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242, USA.
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224
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Camurri L, Mambetisaeva E, Davies D, Parnavelas J, Sundaresan V, Andrews W. Evidence for the existence of two Robo3 isoforms with divergent biochemical properties. Mol Cell Neurosci 2005; 30:485-93. [PMID: 16226035 DOI: 10.1016/j.mcn.2005.07.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Revised: 07/22/2005] [Accepted: 07/25/2005] [Indexed: 11/18/2022] Open
Abstract
Robo3 is a member of the roundabout (Robo) family of proteins that plays a key role in axon guidance and cell migration in the developing nervous system. Recent studies have shown that Robo3 plays a crucial role in controlling axon guidance at the midline of the CNS. Here we describe and compare two human Robo3 isoforms, Robo3A and Robo3B, which differ by the insertion of 26 amino acids at the N-terminus, and these forms appear to be evolutionary conserved. We investigated the bioactivity of these isoforms and show that they have different binding properties to Slit, and that orthologs of these forms are expressed in the mouse embryo. In addition, we show that, like other members of the Robo family, Robo3 can bind homophilically, but it is also capable of binding heterophilically to Robo1 and NCAM. We propose that these properties of Robo3 may contribute to its function at the midline of the CNS.
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Affiliation(s)
- Laura Camurri
- MRC Centre for Developmental Neurobiology, New Hunt's House, King's College, London, Guy's Campus, London SE1 1UL, UK
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225
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Galler AB, García Arguinzonis MI, Baumgartner W, Kuhn M, Smolenski A, Simm A, Reinhard M. VASP-dependent regulation of actin cytoskeleton rigidity, cell adhesion, and detachment. Histochem Cell Biol 2005; 125:457-74. [PMID: 16267652 DOI: 10.1007/s00418-005-0091-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2005] [Indexed: 01/13/2023]
Abstract
Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) proteins are established regulators of actin-based motility, platelet aggregation, and growth cone guidance. However, the molecular mechanisms involved essentially remain elusive. Here we report on a novel mechanism of VASP action, namely the regulation of tensile strength, contractility, and rigidity of the actin cytoskeleton. Compared to wild-type cells fibroblasts derived from VASP-deficient mice have thicker and more stable actin stress fibres. Furthermore focal adhesions are enlarged, myosin light chain phosphorylation is increased, and the rigidity of the filament-supported plasma membrane is elevated about three- to fourfold, as is evident from atomic force microscopy. Moreover, fibronectin-coated beads adhere stronger to the surface of VASP-deficient cells. The resistance of these beads to mechanical displacement by laser tweezers is dramatically increased in an F-actin-dependent mode. Cytoskeletal stabilization coincides with slower cell adhesion and detachment, while overall adhesion is increased. Interestingly, many of these effects observed in VASP (-/-) cells are recapitulated in VASP-overexpressing cells, hinting towards a balanced stoichiometry necessary for appropriate VASP function. Taken together, our results suggest that VASP regulates surface protrusion formation and cell adhesion through modulation of the mechanical properties of the actin cytoskeleton.
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Affiliation(s)
- Annette B Galler
- Institute for Clinical Biochemistry and Pathobiochemistry, University of Würzburg, Josef-Schneider-Str. 2, 97080, Würzburg, Germany
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226
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Kalil K, Dent EW. Touch and go: guidance cues signal to the growth cone cytoskeleton. Curr Opin Neurobiol 2005; 15:521-6. [PMID: 16143510 DOI: 10.1016/j.conb.2005.08.005] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Accepted: 08/24/2005] [Indexed: 11/19/2022]
Abstract
Growth cones, the highly motile tips of growing axons, guide axons to their targets by responding to molecular cues. Growth cone behaviors such as advancing, retracting, turning and branching are driven by the dynamics and reorganization of the actin and microtubule cytoskeleton through signaling pathways linked to guidance cue receptors. Actin filaments play a major part in growth cone motility, and because of their peripheral locations were thought to be the primary target of molecular cues. However, recent studies have shown that dynamic microtubules can penetrate the growth cone periphery where guidance molecules can influence them directly. Moreover, guidance cues can regulate growth cone steering by modulating dynamic actin-microtubule interactions.
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Affiliation(s)
- Katherine Kalil
- Department of Anatomy, University of Wisconsin-Madison, 1300 University Avenue, Madison, WI 53706, USA.
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227
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Hannula-Jouppi K, Kaminen-Ahola N, Taipale M, Eklund R, Nopola-Hemmi J, Kääriäinen H, Kere J. The axon guidance receptor gene ROBO1 is a candidate gene for developmental dyslexia. PLoS Genet 2005; 1:e50. [PMID: 16254601 PMCID: PMC1270007 DOI: 10.1371/journal.pgen.0010050] [Citation(s) in RCA: 216] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2005] [Accepted: 09/21/2005] [Indexed: 11/21/2022] Open
Abstract
Dyslexia, or specific reading disability, is the most common learning disorder with a complex, partially genetic basis, but its biochemical mechanisms remain poorly understood. A locus on Chromosome 3, DYX5, has been linked to dyslexia in one large family and speech-sound disorder in a subset of small families. We found that the axon guidance receptor gene ROBO1, orthologous to the Drosophila roundabout gene, is disrupted by a chromosome translocation in a dyslexic individual. In a large pedigree with 21 dyslexic individuals genetically linked to a specific haplotype of ROBO1 (not found in any other chromosomes in our samples), the expression of ROBO1 from this haplotype was absent or attenuated in affected individuals. Sequencing of ROBO1 in apes revealed multiple coding differences, and the selection pressure was significantly different between the human, chimpanzee, and gorilla branch as compared to orangutan. We also identified novel exons and splice variants of ROBO1 that may explain the apparent phenotypic differences between human and mouse in heterozygous loss of ROBO1. We conclude that dyslexia may be caused by partial haplo-insufficiency for ROBO1 in rare families. Thus, our data suggest that a slight disturbance in neuronal axon crossing across the midline between brain hemispheres, dendrite guidance, or another function of ROBO1 may manifest as a specific reading disability in humans.
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Affiliation(s)
| | | | - Mikko Taipale
- Department of Medical Genetics, University of Helsinki, Finland
- European Molecular Biology Laboratory, Gene Expression Programme, Heidelberg, Germany
| | - Ranja Eklund
- Department of Medical Genetics, University of Helsinki, Finland
| | - Jaana Nopola-Hemmi
- Department of Medical Genetics, University of Helsinki, Finland
- Department of Pediatrics, Jorvi Hospital, Espoo, Finland
| | - Helena Kääriäinen
- Department of Medical Genetics, The Family Federation of Finland, Helsinki, Finland
- Department of Medical Genetics, University of Turku, Turku, Finland
| | - Juha Kere
- Department of Medical Genetics, University of Helsinki, Finland
- Department of Biosciences at Novum and Clinical Research Centre, Karolinska Institutet, Stockholm, Sweden
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228
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Klagsbrun M, Eichmann A. A role for axon guidance receptors and ligands in blood vessel development and tumor angiogenesis. Cytokine Growth Factor Rev 2005; 16:535-48. [PMID: 15979925 DOI: 10.1016/j.cytogfr.2005.05.002] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Nerves and blood vessels resemble each other in their ability to form branching networks. They are in close proximity suggesting possible molecular interactions. The patterning of nerves and blood vessels are not random but are regulated by attractive and repulsive cues. Four major neuronal guidance factors that are sensed by growth cones have been identified, Semaphorin, Ephrin, Slit and Netrin, and their cognate receptors, neuropilin, Eph, roundabouts (Robo) and uncoordinated-5 (UNC5). Unexpectedly, these ligand/receptor pairs also regulate developmental and tumor angiogenesis. Together, there is strong evidence that development of the nervous and vascular systems are regulated by common cues.
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Affiliation(s)
- Michael Klagsbrun
- Vascular Biology Program, Department of Surgery, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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229
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Ghenea S, Boudreau JR, Lague NP, Chin-Sang ID. The VAB-1 Eph receptor tyrosine kinase and SAX-3/Robo neuronal receptors function together during C. elegans embryonic morphogenesis. Development 2005; 132:3679-90. [PMID: 16033794 DOI: 10.1242/dev.01947] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Mutations that affect the single C. elegans Eph receptor tyrosine kinase VAB-1 cause defects in cell movements during embryogenesis. Here, we provide genetic and molecular evidence that the VAB-1 Eph receptor functions with another neuronal receptor, SAX-3/Robo, for proper embryogenesis. Our analysis of sax-3 mutants shows that SAX-3/Robo functions with the VAB-1 Eph receptor for gastrulation cleft closure and ventral epidermal enclosure. In addition, SAX-3 functions autonomously for epidermal morphogenesis independently of VAB-1. A double-mutant combination between vab-1 and slt-1 unmasks a role for the SLT-1 ligand in embryogenesis. We provide evidence for a physical interaction between the VAB-1 tyrosine kinase domain and the juxtamembrane and CC1 region of the SAX-3/Robo receptor. Gene dosage, non-allelic non-complementation experiments and co-localization of the two receptors are consistent with a model in which these two receptors form a complex and function together during embryogenesis.
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Affiliation(s)
- Simona Ghenea
- Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada
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230
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Jia L, Cheng L, Raper J. Slit/Robo signaling is necessary to confine early neural crest cells to the ventral migratory pathway in the trunk. Dev Biol 2005; 282:411-21. [PMID: 15950606 DOI: 10.1016/j.ydbio.2005.03.021] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2004] [Revised: 03/09/2005] [Accepted: 03/21/2005] [Indexed: 10/25/2022]
Abstract
Neural crest cells migrate along two discrete pathways within the trunk of developing embryos. In the chick, early migrating crest cells are confined to a ventral pathway medial to the dermamyotome while later cells migrate on a dorsal pathway lateral to the dermamyotome. Here we show that Slits are expressed in the dermamyotome, that early migrating crest cells express the Slit receptors Robo 1 and Robo 2, that Slit2 repels migrating crest cells in an in vitro assay, and that the misexpression of a dominant-negative Robo1 receptor induces a significant fraction of early crest cells to migrate ectopically in the dorso-lateral pathway. These findings suggest that Slits, most likely those expressed in the dermamyotome, help to confine the migration of early crest cells to the ventral pathway.
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Affiliation(s)
- Li Jia
- Department of Neuroscience, University of Pennsylvania School of Medicine, 1115, BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
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231
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Menzies AS, Aszodi A, Williams SE, Pfeifer A, Wehman AM, Goh KL, Mason CA, Fassler R, Gertler FB. Mena and vasodilator-stimulated phosphoprotein are required for multiple actin-dependent processes that shape the vertebrate nervous system. J Neurosci 2005; 24:8029-38. [PMID: 15371503 PMCID: PMC6729793 DOI: 10.1523/jneurosci.1057-04.2004] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ena/vasodilator-stimulated phosphoprotein (VASP) proteins regulate the geometry of the actin cytoskeleton, thereby influencing cell morphology and motility. Analysis of invertebrate mutants implicates Ena/VASP function in several actin-dependent processes such as axon and dendritic guidance, cell migration, and dorsal closure. In vertebrates, genetic analysis of Ena/VASP function is hindered by the broad and overlapping expression of the three highly related family members Mena (Mammalian enabled), VASP, and EVL (Ena-VASP like). Mice deficient in either Mena or VASP exhibit subtle defects in forebrain commissure formation and platelet aggregation, respectively. In this study, we investigated the consequence of deleting both Mena and VASP. Mena-/-VASP-/- double mutants die perinatally and display defects in neurulation, craniofacial structures, and the formation of several fiber tracts in the CNS and peripheral nervous system.
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Affiliation(s)
- A Sheila Menzies
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
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232
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Abstract
How axons in the developing nervous system successfully navigate to their correct targets is a fundamental problem in neurobiology. Understanding the mechanisms that mediate axon guidance will give important insight into how the nervous system is correctly wired during development and may have implications for therapeutic approaches to developmental brain disorders and nerve regeneration. Achieving this understanding will require unraveling the molecular logic that ensures the proper expression and localization of axon guidance cues and receptors, and elucidating the signaling events that regulate the growth cone cytoskeleton in response to guidance receptor activation. Studies of axon guidance at the midline of many experimental systems, from the ventral midline of Drosophila to the vertebrate spinal cord, have led to important mechanistic insights into the complex problem of wiring the nervous system. Here we review recent advances in understanding the regulation of midline axon guidance, with a particular emphasis on the contributions made from molecular genetic studies of invertebrate model systems.
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Affiliation(s)
- David S Garbe
- Department of Neuroscience, University of Pennsylvania, School of Medicine, Philadelphia, PA 19104, USA
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233
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Bhat KM. Slit-roundabout signaling neutralizes netrin-Frazzled-mediated attractant cue to specify the lateral positioning of longitudinal axon pathways. Genetics 2005; 170:149-59. [PMID: 15716500 PMCID: PMC1449716 DOI: 10.1534/genetics.104.036863] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Accepted: 01/26/2005] [Indexed: 11/18/2022] Open
Abstract
An extending axon growth cone is subjected to attractant and repellent cues. It is not clear how these growth cones discriminate the two opposing forces and select their projection paths. Here, we report that in the Drosophila nerve cord the growth cones of longitudinal tracts are subjected to attraction by the Netrin-Frazzled pathway. However, the midline Slit neutralizes this pathway in a Robo-dependent manner and prevents Netrin-Frazzled-mediated attraction of longitudinal tracts. Our results suggest that the loss of a neutralizing effect on the Netrin-mediated attraction is responsible for the longitudinal tracts entering the midline in slit mutants as opposed to a loss of repulsion as is currently believed. This effect is not via a direct inhibition of Frazzled by Robo; instead, it is at a level downstream of Frazzled. Thus, the growth cones of longitudinal tracts subjected to two opposing forces are able to block one with the other and specify their correct lateral positioning along the midline.
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Affiliation(s)
- Krishna Moorthi Bhat
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322
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234
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Badour K, Zhang J, Siminovitch KA. Involvement of the Wiskott-Aldrich syndrome protein and other actin regulatory adaptors in T cell activation. Semin Immunol 2005; 16:395-407. [PMID: 15541654 DOI: 10.1016/j.smim.2004.08.019] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The actin cytoskeleton is a dynamic structure recognized for many years as integral to the coupling of external stimuli to cell activation and ensuing changes in morphology and movement. It is only recently, however, that a molecular understanding of actin involvement in these activities has emerged coincident with the identification of cytosolic signaling effectors that couple extracellular stimuli to induction of actin nucleation. Notable among these actin regulatory effectors are members of the Wiskott-Aldrich syndrome protein (WASp) family, a group of cytoskeletal adaptors imbued with the capacity to connect various signal transduction pathways to the Arp 2/3 complex and Arp 2/3-mediated actin polymerization. In T cells, the functional characterization of WASp and other actin-modulatory adaptors has proved instrumental in delineating the molecular interactions evoking actin cytoskeletal reorganization downstream of antigen receptor engagement and in clarifying the influence of actin-based processes on T cell activation. In this review, the structural and functional properties of the major actin regulatory cytoskeletal adaptors in T cells are described with an emphasis on the roles of these proteins in fostering the TCR actin cytoskeletal interplay required for induction of T cell activation and expression of dynamic effector responses.
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Affiliation(s)
- Karen Badour
- Department of Medicine, McLaughlin Centre of Molecular Medicine, University of Toronto, Mount Sinai Hospital, Samuel Lunenfeld and Toronto General Hospital Research Institutes, 600 University Avenue, #656A, Toronto, Ont., Canada M5G 1X5.
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235
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Forsthoefel DJ, Liebl EC, Kolodziej PA, Seeger MA. The Abelson tyrosine kinase, the Trio GEF and Enabled interact with the Netrin receptor Frazzled in Drosophila. Development 2005; 132:1983-94. [PMID: 15790972 DOI: 10.1242/dev.01736] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The attractive Netrin receptor Frazzled (Fra), and the signaling molecules Abelson tyrosine kinase (Abl), the guanine nucleotide-exchange factor Trio,and the Abl substrate Enabled (Ena), all regulate axon pathfinding at the Drosophila embryonic CNS midline. We detect genetic and/or physical interactions between Fra and these effector molecules that suggest that they act in concert to guide axons across the midline. Mutations in Abland trio dominantly enhance fra and Netrin mutant CNS phenotypes, and fra;Abl and fra;trio double mutants display a dramatic loss of axons in a majority of commissures. Conversely,heterozygosity for ena reduces the severity of the CNS phenotype in fra, Netrin and trio,Abl mutants. Consistent with an in vivo role for these molecules as effectors of Fra signaling, heterozygosity for Abl, trio or ena reduces the number of axons that inappropriately cross the midline in embryos expressing the chimeric Robo-Fra receptor. Fra interacts physically with Abl and Trio in GST-pulldown assays and in co-immunoprecipitation experiments. In addition, tyrosine phosphorylation of Trio and Fra is elevated in S2 cells when Abl levels are increased. Together, these data suggest that Abl, Trio, Ena and Fra are integrated into a complex signaling network that regulates axon guidance at the CNS midline.
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Affiliation(s)
- David J Forsthoefel
- The Ohio State University, Department of Molecular Genetics and Center for Molecular Neurobiology, Columbus, OH 43210, USA
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236
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Hu H, Li M, Labrador JP, McEwen J, Lai EC, Goodman CS, Bashaw GJ. Cross GTPase-activating protein (CrossGAP)/Vilse links the Roundabout receptor to Rac to regulate midline repulsion. Proc Natl Acad Sci U S A 2005; 102:4613-8. [PMID: 15755809 PMCID: PMC555501 DOI: 10.1073/pnas.0409325102] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The regulators of the Rho-family GTPases, GTPase-activating proteins (GAPs) and guanine exchange factors (GEFs), play important roles in axon guidance. By means of a functional genomic study of the Rho-family GEFs and GAPs in Drosophila, we have identified a Rho-family GAP, CrossGAP (CrGAP), which is involved in Roundabout (Robo) receptor-mediated repulsive axon guidance. CrGAP physically associates with the Robo receptor. Too much or too little CrGAP activity leads to defects in Robo-mediated repulsion at the midline choice point. The CrGAP gain-of-function phenotype mimics the loss-of-function phenotypes of both Robo and Rac. Dosage-sensitive genetic interactions among CrGAP, Robo, and Rac support a model in which CrGAP transduces signals downstream of Robo receptor to regulate Rac-dependent cytoskeletal changes.
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Affiliation(s)
- Hailan Hu
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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237
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Withee J, Galligan B, Hawkins N, Garriga G. Caenorhabditis elegans WASP and Ena/VASP proteins play compensatory roles in morphogenesis and neuronal cell migration. Genetics 2005; 167:1165-76. [PMID: 15280232 PMCID: PMC1470955 DOI: 10.1534/genetics.103.025676] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We report here that WASP and Ena/VASP family proteins play overlapping roles in C. elegans morphogenesis and neuronal cell migration. Specifically, these studies demonstrate that UNC-34/Ena plays a role in morphogenesis that is revealed only in the absence of WSP-1 function and that WSP-1 has a role in neuronal cell migration that is revealed only in the absence of UNC-34/Ena activity. To identify additional genes that act in parallel to unc-34/ena during morphogenesis, we performed a screen for synthetic lethals in an unc-34 null mutant background utilizing an RNAi feeding approach. To our knowledge, this is the first reported RNAi-based screen for genetic interactors. As a result of this screen, we identified a second C. elegans WASP family protein, wve-1, that is most homologous to SCAR/WAVE proteins. Animals with impaired wve-1 function display defects in gastrulation, fail to undergo proper morphogenesis, and exhibit defects in neuronal cell migrations and axon outgrowth. Reducing wve-1 levels in either unc-34/ena or wsp-1 mutant backgrounds also leads to a significant enhancement of the gastrulation and morphogenesis defects. Thus, unc-34/ena, wsp-1, and wve-1 play overlapping roles during embryogenesis and unc-34/ena and wsp-1 play overlapping roles in neuronal cell migration. These observations show that WASP and Ena/VASP proteins can compensate for each other in vivo and provide the first demonstration of a role for Ena/VASP proteins in gastrulation and morphogenesis. In addition, our results provide the first example of an in vivo role for WASP family proteins in neuronal cell migrations and cytokinesis in metazoans.
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Affiliation(s)
- Jim Withee
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204, USA
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238
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Keleman K, Ribeiro C, Dickson BJ. Comm function in commissural axon guidance: cell-autonomous sorting of Robo in vivo. Nat Neurosci 2005; 8:156-63. [PMID: 15657595 DOI: 10.1038/nn1388] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2004] [Accepted: 12/23/2004] [Indexed: 11/09/2022]
Abstract
Commissureless (Comm) controls axon guidance across the Drosophila melanogaster midline by regulating surface levels of Robo, the receptor for the midline repellent Slit. Two different models have been proposed for how Comm regulates Robo: a 'sorting' model and a 'clearance' model, both based on studies using heterologous cells in vitro. Here, we test these two models in vivo. We establish a genetic rescue assay for Comm, and use this assay to show that midline crossing does not require the presence of Comm in midline cells, as proposed by the clearance model. Moreover, by monitoring the trafficking of a Robo-green fluorescent protein (GFP) fusion in living embryos, we demonstrate that Comm prevents the delivery of Robo-GFP to the growth cone, as predicted by the sorting model. It has also been suggested that Comm must be ubiquitinated by the Nedd4 ubiquitin ligase. We show here, however, that ubiquitination of Comm is not required for its function in vitro or in vivo, and that Nedd4 is unlikely to function in axon guidance at the midline.
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Affiliation(s)
- Krystyna Keleman
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Dr. Bohr-Gasse 3-5, A-1030 Vienna, Austria
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239
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Yeo SY, Miyashita T, Fricke C, Little MH, Yamada T, Kuwada JY, Huh TL, Chien CB, Okamoto H. Involvement of Islet-2 in the Slit signaling for axonal branching and defasciculation of the sensory neurons in embryonic zebrafish. Mech Dev 2005; 121:315-24. [PMID: 15110042 DOI: 10.1016/j.mod.2004.03.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2003] [Revised: 03/15/2004] [Accepted: 03/15/2004] [Indexed: 11/21/2022]
Abstract
In Drosophila melanogaster, Slit acts as a repulsive cue for the growth cones of the commissural axons which express a receptor for Slit, Roundabout (Robo), thus preventing the commissural axons from crossing the midline multiple times. Experiments using explant culture have shown that vertebrate Slit homologues also act repulsively for growth cone navigation and neural migration, and promote branching and elongation of sensory axons. Here, we demonstrate that overexpression of Slit2 in vivo in transgenic zebrafish embryos severely affected the behavior of the commissural reticulospinal neurons (Mauthner neurons), promoted branching of the peripheral axons of the trigeminal sensory ganglion neurons, and induced defasciculation of the medial longitudinal fascicles. In addition, Slit2 overexpression caused defasciculation and deflection of the central axons of the trigeminal sensory ganglion neurons from the hindbrain entry point. The central projection was restored by either functional repression or mutation of Robo2, supporting its role as a receptor mediating the Slit signaling in vertebrate neurons. Furthermore, we demonstrated that Islet-2, a LIM/homeodomain-type transcription factor, is essential for Slit2 to induce axonal branching of the trigeminal sensory ganglion neurons, suggesting that factors functioning downstream of Islet-2 are essential for mediating the Slit signaling for promotion of axonal branching.
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Affiliation(s)
- Sang-Yeob Yeo
- Laboratory for Developmental Gene Regulation, RIKEN Brain Science Institute, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
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240
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Abstract
Blood vessels and nerves are structured in architecturally similar organ systems and show functional relationships. Indeed, vascular and neuronal cells are guided in their journey throughout the body by the same attractive and repulsive factors that respectively activate and inhibit the function of integrin-adhesive receptors.
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Affiliation(s)
- Guido Serini
- Division of Molecular Angiogenesis, Institute for Cancer Research and Treatment, Department of Oncological Sciences, University of Torino School of Medicine, 10060 Candiolo (TO), Italy.
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241
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Galletta BJ, Chakravarti M, Banerjee R, Abmayr SM. SNS: adhesive properties, localization requirements and ectodomain dependence in S2 cells and embryonic myoblasts. Mech Dev 2004; 121:1455-68. [PMID: 15511638 DOI: 10.1016/j.mod.2004.08.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2004] [Revised: 07/20/2004] [Accepted: 08/04/2004] [Indexed: 11/30/2022]
Abstract
The body wall muscles in the Drosophila larva arise from interactions between Duf/Kirre and Irregular chiasm C-roughest (IrreC-rst)-expressing founder myoblasts and sticks-and-stones (SNS)-expressing fusion competent myoblasts in the embryo. Herein, we demonstrate that SNS mediates heterotypic adhesion of S2 cells with Duf/Kirre and IrreC-rst-expressing S2 cells, and colocalizes with these proteins at points of cell contact. These properties are independent of their transmembrane and cytoplasmic domains, and are observed quite readily with GPI-anchored forms of the ectodomains. Heterotypic interactions between Duf/Kirre and SNS-expressing S2 cells occur more rapidly and to a greater extent than homotypic interactions with other Duf/Kirre-expressing cells. In addition, Duf/Kirre and SNS are present in an immunoprecipitable complex from S2 cells. In the embryo, Duf/Kirre and SNS are present at points of contact between founder and fusion competent cells. Moreover, SNS clustering on the cell surface is dependent on Duf/Kirre and/or IrreC-rst. Finally, although the cytoplasmic and transmembrane domains of SNS are expendable for interactions in culture, they are essential for fusion of embryonic myoblasts.
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Affiliation(s)
- Brian J Galletta
- Stowers Institute for Medical Research, 1000 E. 50th St., Kansas City, MO 64110, USA
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242
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Krause M, Leslie JD, Stewart M, Lafuente EM, Valderrama F, Jagannathan R, Strasser GA, Rubinson DA, Liu H, Way M, Yaffe MB, Boussiotis VA, Gertler FB. Lamellipodin, an Ena/VASP ligand, is implicated in the regulation of lamellipodial dynamics. Dev Cell 2004; 7:571-83. [PMID: 15469845 DOI: 10.1016/j.devcel.2004.07.024] [Citation(s) in RCA: 257] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2003] [Revised: 05/25/2004] [Accepted: 07/19/2004] [Indexed: 01/20/2023]
Abstract
Lamellipodial protrusion is regulated by Ena/VASP proteins. We identified Lamellipodin (Lpd) as an Ena/VASP binding protein. Both proteins colocalize at the tips of lamellipodia and filopodia. Lpd is recruited to EPEC and Vaccinia, pathogens that exploit the actin cytoskeleton for their own motility. Lpd contains a PH domain that binds specifically to PI(3,4)P2, an asymmetrically localized signal in chemotactic cells. Lpd's PH domain can localize to ruffles in PDGF-treated fibroblasts. Lpd overexpression increases lamellipodial protrusion velocity, an effect observed when Ena/VASP proteins are overexpressed or artificially targeted to the plasma membrane. Conversely, knockdown of Lpd expression impairs lamellipodia formation, reduces velocity of residual lamellipodial protrusion, and decreases F-actin content. These phenotypes are more severe than loss of Ena/VASP, suggesting that Lpd regulates other effectors of the actin cytoskeleton in addition to Ena/VASP.
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Affiliation(s)
- Matthias Krause
- Department of Biology and Center for Cancer Research, MIT, Cambridge, MA 02139, USA
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243
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Toyofuku T, Zhang H, Kumanogoh A, Takegahara N, Yabuki M, Harada K, Hori M, Kikutani H. Guidance of myocardial patterning in cardiac development by Sema6D reverse signalling. Nat Cell Biol 2004; 6:1204-11. [PMID: 15543137 DOI: 10.1038/ncb1193] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Accepted: 10/27/2004] [Indexed: 11/09/2022]
Abstract
Cardiac chamber formation involves dynamic changes in myocardial organization, including trabeculation and expansion of the compact layer. The positional cues that regulate myocardial patterning, however, remain unclear. Through ligation of the Plexin-A1 receptor, the transmembrane-type semaphorin Sema6D regulates endocardial cell migration. Here, we demonstrate that knockdown of either Sema6D or Plexin-A1 leads to the generation of a small, thin ventricular compact layer and to defective trabeculation. In the heart, expression of the Plexin-A1 extracellular domain alone can rescue the defective trabeculation induced by suppression of Plexin-A1, but not that resulting from defective Sema6D expression. This indicates that reverse signalling by Sema6D occurs within the myocardium. In a ligand-dependent manner, Abl kinase is recruited to the cytoplasmic tail of Sema6D and activated, resulting in phosphorylation of Enabled and dissociation from Sema6D. Constitutive activation of Sema6D signalling enhances the migration of myocardial cells into the trabeculae, whereas inhibition arrests cells within the compact layer. Thus, Sema6D coordinates both compact-layer expansion and trabeculation, functioning as both a ligand and a receptor for Plexin-A1.
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MESH Headings
- Animals
- Cell Movement/genetics
- Chick Embryo
- DNA-Binding Proteins/metabolism
- Heart/embryology
- Heart Defects, Congenital/genetics
- Heart Defects, Congenital/metabolism
- Humans
- Ligands
- Myocardium/cytology
- Myocardium/metabolism
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/metabolism
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/metabolism
- Oncogene Proteins v-abl/genetics
- Oncogene Proteins v-abl/metabolism
- Organogenesis/physiology
- Phosphorylation
- Protein Structure, Tertiary/genetics
- RNA Interference
- RNA, Messenger/metabolism
- Receptors, Cell Surface/deficiency
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/isolation & purification
- Receptors, Cell Surface/metabolism
- Semaphorins/deficiency
- Semaphorins/genetics
- Semaphorins/isolation & purification
- Semaphorins/metabolism
- Signal Transduction/genetics
- Signal Transduction/physiology
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Affiliation(s)
- Toshihiko Toyofuku
- Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
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244
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Howitt JA, Clout NJ, Hohenester E. Binding site for Robo receptors revealed by dissection of the leucine-rich repeat region of Slit. EMBO J 2004; 23:4406-12. [PMID: 15496984 PMCID: PMC526463 DOI: 10.1038/sj.emboj.7600446] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Accepted: 09/22/2004] [Indexed: 11/08/2022] Open
Abstract
Recognition of the large secreted protein Slit by receptors of the Robo family provides fundamental signals in axon guidance and other developmental processes. In Drosophila, Slit-Robo signalling regulates midline crossing and the lateral position of longitudinal axon tracts. We report the functional dissection of Drosophila Slit, using structure analysis, site-directed mutagenesis and in vitro assays. The N-terminal region of Slit consists of a tandem array of four independently folded leucine-rich repeat (LRR) domains, connected by disulphide-tethered linkers. All three Drosophila Robos were found to compete for a single highly conserved site on the concave face of the second LRR domain of Slit. We also found that this domain is sufficient for biological activity in a chemotaxis assay. Other Slit activities may require Slit dimerisation mediated by the fourth LRR domain. Our results show that a small portion of Slit is able to induce Robo signalling and indicate that the distinct functions of Drosophila Robos are encoded in their divergent cytosolic domains.
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MESH Headings
- Amino Acid Sequence
- Animals
- Axons/physiology
- Binding Sites
- Cell Line
- Cell Movement
- Cells, Cultured
- Chromatography, Gel
- Conserved Sequence
- Crystallography, X-Ray
- Culture Media, Conditioned
- Cysteine/chemistry
- Drosophila/chemistry
- Drosophila/genetics
- Drosophila/metabolism
- Drosophila Proteins/chemistry
- Drosophila Proteins/isolation & purification
- Drosophila Proteins/metabolism
- Endothelium, Vascular/cytology
- Humans
- Leucine/chemistry
- Leucine/genetics
- Leucine/metabolism
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Nerve Tissue Proteins/chemistry
- Nerve Tissue Proteins/isolation & purification
- Nerve Tissue Proteins/metabolism
- Protein Binding
- Protein Structure, Tertiary
- Receptors, Immunologic/isolation & purification
- Receptors, Immunologic/metabolism
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/metabolism
- Repetitive Sequences, Amino Acid
- Sequence Homology, Amino Acid
- Umbilical Veins/cytology
- Water/chemistry
- Roundabout Proteins
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Affiliation(s)
- Jason A Howitt
- Department of Biological Sciences, Imperial College London, London, UK.
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245
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Kraut R, Zinn K. Roundabout 2 regulates migration of sensory neurons by signaling in trans. Curr Biol 2004; 14:1319-29. [PMID: 15296748 PMCID: PMC3566263 DOI: 10.1016/j.cub.2004.07.052] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2003] [Revised: 06/08/2004] [Accepted: 06/21/2004] [Indexed: 10/26/2022]
Abstract
BACKGROUND Roundabout (Robo) receptors and their ligand Slit are important regulators of axon guidance and cell migration. The development of Drosophila embryonic sense organs provides a neuronal migration paradigm where the in vivo roles of Slit and Robo can be assayed using genetics. RESULTS Here we show that Slit-Robo signaling controls migration of Drosophila larval sensory neurons that are part of the Chordotonal (Cho) stretch receptor organs. We used live imaging to show that abdominal Cho organs normally migrate ventrally during development, whereas thoracic Cho organs do not. Robo2 overexpression in cis (in the sensory neurons) or in trans (on neighboring visceral mesoderm) transforms abdominal organs to a thoracic morphology and position by blocking migration, while loss of Slit-Robo signaling produces a reverse transformation in which thoracic organs migrate ectopically. Rescue and tissue-specific knockout experiments indicate that trans signaling by Robo2 contributes to the normal positioning of the thoracic Cho organs. The differential positioning of Cho organs between the thorax and abdomen is known to be regulated by Hox genes, and we show that the essential Hox cofactor Homothorax, represses Robo2 expression in the abdominal visceral mesoderm. CONCLUSIONS Our results suggest that segment-specific neuronal migration patterns are directed through a novel signaling complex (the "Slit sandwich") in which Robo2 on the thoracic visceral mesoderm binds to Slit and presents it to Robo receptors on Cho neurons. The differential positioning of Cho organs between thorax and abdomen may be determined by Hox gene-mediated repression of robo2.
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246
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Boukhelifa M, Parast MM, Bear JE, Gertler FB, Otey CA. Palladin is a novel binding partner for Ena/VASP family members. ACTA ACUST UNITED AC 2004; 58:17-29. [PMID: 14983521 DOI: 10.1002/cm.10173] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Palladin is an actin-associated protein that contains proline-rich motifs within its amino-terminal sequence that are similar to motifs found in zyxin, vinculin, and the Listeria protein ActA. These motifs are known to be potential binding sites for the Vasodilator-Stimulated Phosphoprotein (VASP). Here, we demonstrate that palladin is an additional direct binding partner for VASP, by using co-immunoprecipitation and blot overlay techniques with both endogenous palladin and recombinant myc-tagged palladin. These results show that VASP binds to full-length palladin and also to the amino-terminal half of palladin, where the polyproline motifs are located. Using a synthetic peptide array, two discrete binding sites for VASP were identified within palladin's proline-rich amino-terminal domain. Using double-label immunofluorescence staining of fully-spread and actively-spreading fibroblasts, the extent of co-localization of palladin and VASP was explored. These proteins were found to strongly co-localize along stress fibers, and partially co-localize in focal adhesions, lamellipodia, and focal complexes. These results suggest that the recently described actin-associated protein palladin may play an important role in recruiting VASP to sites of actin filament growth, anchorage, and crosslinking.
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Affiliation(s)
- Malika Boukhelifa
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, 27599-7545, USA
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247
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Abstract
A hostile environment and decreased regenerative capacity may contribute to the failure of axon regeneration in the adult central nervous system. Recent studies leading to the identification of several myelin-associated inhibitors and their signaling molecules provide opportunitities to assess the contribution of these inhibitory molecules in restricting axon regeneration. These findings may ultimately allow for the development of strategies to alleviate the inhibitory effects of such molecules in an effort to encourage axon regeneration after spinal cord and brain injury.
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Affiliation(s)
- Zhigang He
- Division of Neuroscience, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
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248
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Miller AL, Wang Y, Mooseker MS, Koleske AJ. The Abl-related gene (Arg) requires its F-actin-microtubule cross-linking activity to regulate lamellipodial dynamics during fibroblast adhesion. ACTA ACUST UNITED AC 2004; 165:407-19. [PMID: 15138293 PMCID: PMC2172189 DOI: 10.1083/jcb.200308055] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Microtubules (MTs) help establish and maintain cell polarity by promoting actin-dependent membrane protrusion at the leading edge of the cell, but the molecular mechanisms that mediate cross-talk between actin and MTs during this process are unclear. We demonstrate that the Abl-related gene (Arg) nonreceptor tyrosine kinase is required for dynamic lamellipodial protrusions after adhesion to fibronectin. arg-/- fibroblasts exhibit reduced lamellipodial dynamics as compared with wild-type fibroblasts, and this defect can be rescued by reexpression of an Arg-yellow fluorescent protein fusion. We show that Arg can bind MTs with high affinity and cross-link filamentous actin (F-actin) bundles and MTs in vitro. MTs concentrate and insert into Arg-induced F-actin-rich cell protrusions. Arg requires both its F-actin-binding domains and its MT-binding domain to rescue the defects in lamellipodial dynamics of arg-/- fibroblasts. These findings demonstrate that Arg can mediate physical contact between F-actin and MTs at the cell periphery and that this cross-linking activity is required for Arg to regulate lamellipodial dynamics in fibroblasts.
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Affiliation(s)
- Ann L Miller
- Department of Molecular Biophysics and Biochemistry, Yale University, SHMC-E31, 333 Cedar St., New Haven, CT 06520, USA
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249
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Lundström A, Gallio M, Englund C, Steneberg P, Hemphälä J, Aspenström P, Keleman K, Falileeva L, Dickson BJ, Samakovlis C. Vilse, a conserved Rac/Cdc42 GAP mediating Robo repulsion in tracheal cells and axons. Genes Dev 2004; 18:2161-71. [PMID: 15342493 PMCID: PMC515293 DOI: 10.1101/gad.310204] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2003] [Accepted: 06/21/2004] [Indexed: 11/25/2022]
Abstract
Slit proteins steer the migration of many cell types through their binding to Robo receptors, but how Robo controls cell motility is not clear. We describe the functional analysis of vilse, a Drosophila gene required for Robo repulsion in epithelial cells and axons. Vilse defines a conserved family of RhoGAPs (Rho GTPase-activating proteins), with representatives in flies and vertebrates. The phenotypes of vilse mutants resemble the tracheal and axonal phenotypes of Slit and Robo mutants at the CNS midline. Dosage-sensitive genetic interactions between vilse, slit, and robo mutants suggest that vilse is a component of robo signaling. Moreover, overexpression of Vilse in the trachea of robo mutants ameliorates the phenotypes of robo, indicating that Vilse acts downstream of Robo to mediate midline repulsion. Vilse and its human homolog bind directly to the intracellular domains of the corresponding Robo receptors and promote the hydrolysis of RacGTP and, less efficiently, of Cdc42GTP. These results together with genetic interaction experiments with robo, vilse, and rac mutants suggest a mechanism whereby Robo repulsion is mediated by the localized inactivation of Rac through Vilse.
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Affiliation(s)
- Annika Lundström
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-106 96 Stockholm, Sweden
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250
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Rodino-Klapac LR, Beattie CE. Zebrafish topped is required for ventral motor axon guidance. Dev Biol 2004; 273:308-20. [PMID: 15328015 DOI: 10.1016/j.ydbio.2004.06.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 05/27/2004] [Accepted: 06/10/2004] [Indexed: 11/21/2022]
Abstract
Zebrafish primary motor axons extend along stereotyped pathways innervating distinct regions of the developing myotome. During development, these axons make stereotyped projections to ventral and dorsal myotome regions. Caudal primary motoneurons, CaPs, pioneer axon outgrowth along ventral myotomes; whereas, middle primary motoneurons, MiPs, extend axons along dorsal myotomes. Although the development and axon outgrowth of these motoneurons has been characterized, cues that determine whether axons will grow dorsally or ventrally have not been identified. The topped mutant was previously isolated in a genetic screen designed to uncover mutations that disrupt primary motor axon guidance. CaP axons in topped mutants fail to enter the ventral myotome at the proper time, stalling at the nascent horizontal myoseptum, which demarcates dorsal from ventral axial muscle. Later developing secondary motor nerves are also delayed in entering the ventral myotome whereas all other axons examined, including dorsally projecting MiP motor axons, are unaffected in topped mutants. Genetic mosaic analysis indicates that Topped function is non-cell autonomous for motoneurons, and when wild-type cells are transplanted into topped mutant embryos, ventromedial fast muscle are the only cell type able to rescue the CaP axon defect. These data suggest that Topped functions in the ventromedial fast muscle and is essential for motor axon outgrowth into the ventral myotome.
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