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Hou ST, Jiang SX, Smith RA. Permissive and repulsive cues and signalling pathways of axonal outgrowth and regeneration. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 267:125-81. [PMID: 18544498 DOI: 10.1016/s1937-6448(08)00603-5] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Successful axonal outgrowth in the adult central nervous system (CNS) is central to the process of nerve regeneration and brain repair. To date, much of the knowledge on axonal guidance and outgrowth comes from studies on neuritogenesis and patterning during development where distal growth cones constantly sample the local environment and respond to specific physical and trophic influences. Opposing permissive (e.g., growth factors) and hostile signals (e.g., repulsive cues) are processed, leading to growth cone remodelling, and a concomitant restructuring of the cytoskeleton, thereby permitting pioneering extension and a potential for establishing synaptic connections. Repulsive cues, such as semaphorins, ephrins and myelin-secreted inhibitory glycoproteins, act through their respective receptors to affect the collapsing or turning of growth cones via several pathways, such as the Rho GTPases signalling which precipitates the cytoskeletal changes. One of the direct modulators of microtubules is the family of brain-specific proteins, collapsin response mediator protein (CRMP). Exciting evidence emerged recently that cleavage of CRMPs in response to injury-activated proteases, such as calpain, signals axonal retraction and neuronal death in adult post-mitotic neurons, while blocking this signal transduction prevents axonal retraction and death following excitotoxic insult and cerebral ischemia. Regeneration is minimal in injured postnatal CNS, albeit the occurrence of some limited remodelling in areas where synaptic plasticity is prevalent. Frequently in the absence of axonal regeneration, there is not only an inevitable loss of functional connections, but also a loss of neurons, such as through the actions of dependence receptors. Deciphering the cues and signalling pathways of axonal guidance and outgrowth may hold the key to fully understanding nerve regeneration and brain repair, thereby opening the way for developing potential therapeutics.
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Affiliation(s)
- Sheng T Hou
- Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada
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252
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Hsouna A, VanBerkum MFA. Abelson tyrosine kinase and Calmodulin interact synergistically to transduce midline guidance cues in the Drosophila embryonic CNS. Int J Dev Neurosci 2007; 26:345-54. [PMID: 18243630 DOI: 10.1016/j.ijdevneu.2007.12.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 12/17/2007] [Accepted: 12/18/2007] [Indexed: 11/18/2022] Open
Abstract
Calmodulin and Abelson tyrosine kinase are key signaling molecules transducing guidance cues at the Drosophila embryonic midline. A reduction in the signaling strength of either pathway alone induces ectopic midline crossing errors in a few segments. When Calmodulin and Abelson signaling levels are simultaneously reduced, the frequency of ectopic crossovers is synergistically enhanced as all segments exhibit crossing errors. But as the level of signaling is further reduced, commissures begin to fuse and large gaps form in the longitudinal connectives. Quantitative analysis suggests that the level of Abelson activity is particularly important. Like Calmodulin, Abelson interacts with son-of-sevenless to increase ectopic crossovers suggesting all three contribute to midline repulsive signaling. Axons cross the midline in almost every segment if Frazzled is co-overexpressed with the Calmodulin inhibitor, but the crossovers induced by the Calmodulin inhibitor itself do not require endogenous Frazzled. Thus, Calmodulin and Abelson tyrosine kinase are key signaling molecules working synergistically to transduce both midline attractive and repulsive cues. While they may function downstream of specific receptors, the emergence of commissural and longitudinal connective defects point to a novel convergence of Calmodulin and Abelson signaling during the regulation of actin and myosin dynamics underlying a guidance decision.
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Affiliation(s)
- Anita Hsouna
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA
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253
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Cebrià F. Regenerating the central nervous system: how easy for planarians! Dev Genes Evol 2007; 217:733-48. [PMID: 17999079 DOI: 10.1007/s00427-007-0188-6] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2007] [Accepted: 10/03/2007] [Indexed: 11/29/2022]
Abstract
The regenerative capabilities of freshwater planarians (Platyhelminthes) are very difficult to match. A fragment as tiny as 1/279th of the planarian body is able to regenerate a whole animal within very few days [Morgan. Arch Entwm 7:364-397 (1898)]. Although the planarian central nervous system (CNS) may appear quite morphologically simple, recent studies have shown it to be more complex at the molecular level, revealing a high degree of molecular compartmentalization in planarian cephalic ganglia. Planarian neural genes include homologues of well-known transcription factors and genes involved in human diseases, neurotransmission, axon guidance, signaling pathways, and RNA metabolism. The availability of hundreds of genes expressed in planarian neurons coupled with the ability to silence them through the use of RNA interference makes it possible to start unraveling the molecular mechanisms underlying CNS regeneration. In this review, I discuss current knowledge on the planarian nervous system and the genes involved in its regeneration, and I discuss some of the important questions that remain to be answered.
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Affiliation(s)
- Francesc Cebrià
- Departament de Genètica, Facultat de Biologia, Institut de Biomedicina de la Universitat de Barcelona (IBUB), Barcelona, Catalunya, Spain.
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254
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Yaron A, Zheng B. Navigating their way to the clinic: emerging roles for axon guidance molecules in neurological disorders and injury. Dev Neurobiol 2007; 67:1216-31. [PMID: 17514715 DOI: 10.1002/dneu.20512] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The mechanisms underlying formation of the basic network of the nervous system are of fundamental interest in developmental neurobiology. During the wiring of the nervous system, newborn neurons send axons that travel long distances to their targets. These axons are directed by environmental cues, known as guidance cues, to their correct destinations. Through extensive studies in vertebrates and invertebrates many of the guidance cues and their receptors have been identified. Recently, guidance molecules have been suggested to have important roles in pathological conditions of the nervous system. Mutations in guidance receptors have been associated with hereditary neurological disorders, and deregulation of guidance cues might be associated with predisposition to epilepsy. In addition, it was suggested that guidance molecules play roles in the ability of the adult nervous system to recover and repair after injury. Thus, molecules that were first discovered as "developmental cues" are now emerging as important factors in neurological disease and injury in the adult.
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Affiliation(s)
- Avraham Yaron
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
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255
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Nural HF, Todd Farmer W, Mastick GS. The Slit receptor Robo1 is predominantly expressed via the Dutt1 alternative promoter in pioneer neurons in the embryonic mouse brain and spinal cord. Gene Expr Patterns 2007; 7:837-45. [PMID: 17826360 PMCID: PMC2080859 DOI: 10.1016/j.modgep.2007.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2007] [Revised: 07/27/2007] [Accepted: 07/31/2007] [Indexed: 10/23/2022]
Abstract
Robo1 is a member of the Roundabout (Robo) family of receptors for the Slit axon guidance cues. In mice (and humans), the Robo1 locus has alternative promoters producing two transcript isoforms, Robo1 and Dutt1. These isoforms have unique 5' termini, predicted to encode distinct N-terminal amino acids, but share the rest of their 3' exons. To determine the spatial expression of the Robo1 and Dutt1 isoforms, we generated isoform-specific RNA probes, and carried out in situ hybridization on E10.5 mouse embryos, the stage in early neuron differentiation when many major axon pathways are established. The two isoforms had distinct expression patterns that partially overlapped. Dutt1 was the predominant isoform, with widespread expression in regions of post-mitotic neurons and neuroepithelial cells. The Robo1 isoform had a distinct expression pattern restricted to subsets of neurons, many of which were Dutt1-negative. Dutt1 was the main isoform expressed in spinal cord commissural neurons. For both probes, the main hybridization signal was limited to two spots in the nuclei of individual cells. This study shows distinct expression patterns for the Dutt1 and Robo1 alternative promoters in the embryonic nervous system.
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256
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Morlot C, Thielens NM, Ravelli RBG, Hemrika W, Romijn RA, Gros P, Cusack S, McCarthy AA. Structural insights into the Slit-Robo complex. Proc Natl Acad Sci U S A 2007; 104:14923-8. [PMID: 17848514 PMCID: PMC1975871 DOI: 10.1073/pnas.0705310104] [Citation(s) in RCA: 141] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Indexed: 01/27/2023] Open
Abstract
Slits are large multidomain leucine-rich repeat (LRR)-containing proteins that provide crucial guidance cues in neuronal and vascular development. More recently, Slits have been implicated in heart morphogenesis, angiogenesis, and tumor metastasis. Slits are ligands for the Robo (Roundabout) receptors, which belong to the Ig superfamily of transmembrane signaling molecules. The Slit-Robo interaction is mediated by the second LRR domain of Slit and the two N-terminal Ig domains of Robo, but the molecular details of this interaction and how it induces signaling remain unclear. Here we describe the crystal structures of the second LRR domain of human Slit2 (Slit2 D2), the first two Ig domains of its receptor Robo1 (Ig1-2), and the minimal complex between these proteins (Slit2 D2-Robo1 Ig1). Slit2 D2 binds with its concave surface to the side of Ig1 with electrostatic and hydrophobic contact regions mediated by residues that are conserved in other family members. Surface plasmon resonance experiments and a mutational analysis of the interface confirm that Ig1 is the primary domain for binding Slit2. These structures provide molecular insight into Slit-Robo complex formation and will be important for the development of novel cancer therapeutics.
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Affiliation(s)
- Cecile Morlot
- *European Molecular Biology Laboratory, 6 Rue Jules Horowitz, BP 181, 38042 Grenoble, France
| | - Nicole M. Thielens
- Laboratoire d'Enzymologie Moleculaire, Institut de Biologie Structurale J. P. Ebel, 38027 Grenoble Cedex 1, France; and
| | - Raimond B. G. Ravelli
- *European Molecular Biology Laboratory, 6 Rue Jules Horowitz, BP 181, 38042 Grenoble, France
| | | | | | - Piet Gros
- Department of Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Stephen Cusack
- *European Molecular Biology Laboratory, 6 Rue Jules Horowitz, BP 181, 38042 Grenoble, France
| | - Andrew A. McCarthy
- *European Molecular Biology Laboratory, 6 Rue Jules Horowitz, BP 181, 38042 Grenoble, France
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257
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Li WC, Cooke T, Sautois B, Soffe SR, Borisyuk R, Roberts A. Axon and dendrite geography predict the specificity of synaptic connections in a functioning spinal cord network. Neural Dev 2007; 2:17. [PMID: 17845723 PMCID: PMC2071915 DOI: 10.1186/1749-8104-2-17] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Accepted: 09/10/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND How specific are the synaptic connections formed as neuronal networks develop and can simple rules account for the formation of functioning circuits? These questions are assessed in the spinal circuits controlling swimming in hatchling frog tadpoles. This is possible because detailed information is now available on the identity and synaptic connections of the main types of neuron. RESULTS The probabilities of synapses between 7 types of identified spinal neuron were measured directly by making electrical recordings from 500 pairs of neurons. For the same neuron types, the dorso-ventral distributions of axons and dendrites were measured and then used to calculate the probabilities that axons would encounter particular dendrites and so potentially form synaptic connections. Surprisingly, synapses were found between all types of neuron but contact probabilities could be predicted simply by the anatomical overlap of their axons and dendrites. These results suggested that synapse formation may not require axons to recognise specific, correct dendrites. To test the plausibility of simpler hypotheses, we first made computational models that were able to generate longitudinal axon growth paths and reproduce the axon distribution patterns and synaptic contact probabilities found in the spinal cord. To test if probabilistic rules could produce functioning spinal networks, we then made realistic computational models of spinal cord neurons, giving them established cell-specific properties and connecting them into networks using the contact probabilities we had determined. A majority of these networks produced robust swimming activity. CONCLUSION Simple factors such as morphogen gradients controlling dorso-ventral soma, dendrite and axon positions may sufficiently constrain the synaptic connections made between different types of neuron as the spinal cord first develops and allow functional networks to form. Our analysis implies that detailed cellular recognition between spinal neuron types may not be necessary for the reliable formation of functional networks to generate early behaviour like swimming.
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Affiliation(s)
- Wen-Chang Li
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
| | - Tom Cooke
- Centre for Theoretical and Computational Neuroscience, University of Plymouth, Plymouth PL4 8AA, UK
| | - Bart Sautois
- Department of Applied Mathematics and Computer Science, Ghent University, Krijgslaan 281-S9, B-9000 Ghent, Belgium
| | - Stephen R Soffe
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
| | - Roman Borisyuk
- Centre for Theoretical and Computational Neuroscience, University of Plymouth, Plymouth PL4 8AA, UK
| | - Alan Roberts
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
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258
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Imondi R, Jevince AR, Helms AW, Johnson JE, Kaprielian Z. Mis-expression of L1 on pre-crossing spinal commissural axons disrupts pathfinding at the ventral midline. Mol Cell Neurosci 2007; 36:462-71. [PMID: 17884558 PMCID: PMC2111042 DOI: 10.1016/j.mcn.2007.08.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Revised: 07/30/2007] [Accepted: 08/06/2007] [Indexed: 10/22/2022] Open
Abstract
In vertebrates, spinal commissural axons project along a transverse path toward and across the floor plate (FP). Post-crossing commissural axons alter their responsiveness to FP-associated guidance cues and turn to project longitudinally in a fasciculated manner prior to extending away from the midline. The upregulation of the neural cell adhesion molecule L1 on crossed commissural axon segments has been proposed to facilitate pathfinding on the contralateral side of the FP. To explore this possibility in vivo, we used Math1 regulatory sequences to target L1 to commissural axons before they cross the ventral midline. L1 mis-expression did not alter the distribution of commissural axon-associated markers or the ventral extension of commissural axons toward the midline. However, commissural axons often stalled or inappropriately projected into the longitudinal plane at the ipsilateral FP margin. These observations suggest that L1-mediated pathfinding decisions are normally delayed until axons have crossed the ventral midline (VM).
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Affiliation(s)
- Ralph Imondi
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Angela R. Jevince
- Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Amy W. Helms
- Departments of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75235
| | - Jane E. Johnson
- Departments of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75235
| | - Zaven Kaprielian
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
- Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461
- Author for correspondence: Zaven Kaprielian, Departments of Pathology and Neuroscience, Albert Einstein College of Medicine, Kennedy Center, Rm. 624, 1410 Pelham Parkway South, Bronx, NY 10461, Phone: (718) 430-2162, Fax: (718) 430-3758,
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259
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Curinga G, Smith GM. Molecular/genetic manipulation of extrinsic axon guidance factors for CNS repair and regeneration. Exp Neurol 2007; 209:333-42. [PMID: 17706643 PMCID: PMC2255571 DOI: 10.1016/j.expneurol.2007.06.026] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Revised: 06/25/2007] [Accepted: 06/25/2007] [Indexed: 11/22/2022]
Abstract
During development, guidance molecules play a key role in the formation of complex circuits required for neural functions. With the cessation of development, this exuberant growth process slows and stabilizes, and inhibitory molecules expressed by glia prevent initial attempts for axonal regeneration. In this review, we discuss the expression patterns and relative contribution of several guidance molecules on the regenerative process. Injury to the immature CNS or species capable of regenerating exhibit a complete or partial recapitulation of their developmental guidance patterns, whereas similar injuries to adult mammals results in altered expression that acts to further hinder regeneration. Manipulations of guidance molecules after injury have been used to control detrimental effects of axon sprouting and target regenerating axons within the spinal cord.
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Affiliation(s)
- Gabrielle Curinga
- Department of Physiology and Spinal Cord and Brain Injury Research Center (SCoBIRC), University of Kentucky, Lexington, KY 40536, USA
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260
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Cebrià F, Guo T, Jopek J, Newmark PA. Regeneration and maintenance of the planarian midline is regulated by a slit orthologue. Dev Biol 2007; 307:394-406. [PMID: 17553481 PMCID: PMC2148499 DOI: 10.1016/j.ydbio.2007.05.006] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Revised: 05/02/2007] [Accepted: 05/04/2007] [Indexed: 01/06/2023]
Abstract
Several families of evolutionarily conserved axon guidance cues orchestrate the precise wiring of the nervous system during embryonic development. The remarkable plasticity of freshwater planarians provides the opportunity to study these molecules in the context of neural regeneration and maintenance. Here we characterize a homologue of the Slit family of guidance cues from the planarian Schmidtea mediterranea. Smed-slit is expressed along the planarian midline, in both dorsal and ventral domains. RNA interference (RNAi) targeting Smed-slit results in the collapse of many newly regenerated tissues at the midline; these include the cephalic ganglia, ventral nerve cords, photoreceptors, and the posterior digestive system. Surprisingly, Smed-slit RNAi knockdown animals also develop morphologically distinguishable, ectopic neural structures near the midline in uninjured regions of intact and regenerating planarians. These results suggest that Smed-slit acts not only as a repulsive cue required for proper midline formation during regeneration but that it may also act to regulate the behavior of neural precursors at the midline in intact planarians.
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Affiliation(s)
- Francesc Cebrià
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, B107 Chemical and Life Sciences Laboratory, 601 South Goodwin Avenue, Urbana, IL 61801, USA
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261
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Tornieri K, Rehder V. Nitric oxide release from a single cell affects filopodial motility on growth cones of neighboring neurons. Dev Neurobiol 2007; 67:1932-43. [PMID: 17874460 DOI: 10.1002/dneu.20572] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Nitric oxide (NO), a gaseous messenger, has been reported to be involved in a variety of functions in the nervous system, ranging from neuronal pathfinding to learning and memory. We have shown previously that the application of NO via NO donors to growth cones of identified Helisoma buccal neurons B5 in vitro induces an increase in filopodial length, a decrease in filopodial number, and a slowing in neurite advance. It is unclear, however, whether NO released from a physiological source would affect growth cone dynamics. Here we used cell bodies of identified neurons known to express the NO synthesizing enzyme nitric oxide synthase (NOS) as a source of constitutive NO production and tested their effect on growth cones of other cells in a sender-receiver paradigm. We showed that B5 cell bodies induced a rapid increase in filopodial length in NO-responsive growth cones, and that this effect was blocked by the NOS inhibitor 7-NI, suggesting that the effect was mediated by NO. Inhibition of soluble guanylyl cyclase (sGC) with ODQ blocked filopodial elongation induced by B5 somata, confirming that NO acted via sGC. We also demonstrate that the effect of NO was reversible and that a cell releasing NO can affect growth cones over a distance of at least 100 microm. Our results suggest that NO released from a physiological source can affect the motility of nearby growth cones and thus should be considered a signaling molecule with the potential to affect the outcome of neuronal pathfinding in vivo.
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Affiliation(s)
- Karine Tornieri
- Department of Biology, Georgia State University, Atlanta, GA 30302-4010, USA
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