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Atkins M, Nicol X, Fassier C. Microtubule remodelling as a driving force of axon guidance and pruning. Semin Cell Dev Biol 2023; 140:35-53. [PMID: 35710759 DOI: 10.1016/j.semcdb.2022.05.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 04/26/2022] [Accepted: 05/31/2022] [Indexed: 01/28/2023]
Abstract
The establishment of neuronal connectivity relies on the microtubule (MT) cytoskeleton, which provides mechanical support, roads for axonal transport and mediates signalling events. Fine-tuned spatiotemporal regulation of MT functions by tubulin post-translational modifications and MT-associated proteins is critical for the coarse wiring and subsequent refinement of neuronal connectivity. The defective regulation of these processes causes a wide range of neurodevelopmental disorders associated with connectivity defects. This review focuses on recent studies unravelling how MT composition, post-translational modifications and associated proteins influence MT functions in axon guidance and/or pruning to build functional neuronal circuits. We here summarise experimental evidence supporting the key role of this network as a driving force for growth cone steering and branch-specific axon elimination. We further provide a global overview of the MT-interactors that tune developing axon behaviours, with a special emphasis on their emerging versatility in the regulation of MT dynamics/structure. Recent studies establishing the key and highly selective role of the tubulin code in the regulation of MT functions in axon pathfinding are also reported. Finally, our review highlights the emerging molecular links between these MT regulation processes and guidance signals that wire the nervous system.
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Affiliation(s)
- Melody Atkins
- INSERM, UMR-S 1270, Institut du Fer à Moulin, Sorbonne Université, F-75005 Paris, France
| | - Xavier Nicol
- Institut de la Vision, Sorbonne Université, INSERM, CNRS, F-75012 Paris, France
| | - Coralie Fassier
- Institut de la Vision, Sorbonne Université, INSERM, CNRS, F-75012 Paris, France.
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2
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Yun T, Ko HR, Ahn J, Jin EJ, Jo JM, Kwon IS, Cho SW, Chang YS, Park WS, Ahn JY. B23/Nucleophosmin promotes reconstitution of synaptic path in hippocampus after injury. Biochem Biophys Res Commun 2019; 508:1082-1087. [PMID: 30553452 DOI: 10.1016/j.bbrc.2018.12.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 12/03/2018] [Accepted: 12/05/2018] [Indexed: 10/27/2022]
Abstract
B23, also known as nucleophosmin (NPM), is multifunctional protein directly implicated in cell proliferation, cell cycle progression, and cell survival. In the current study, in addition to confirming its anti-apoptotic function in neuronal survival, we demonstrated that the spatial-temporal expression profile of B23 during development of hippocampal neurons is high in the embryonic stage, down-regulated after birth, and preferentially localized at the tips of growing neuritis and branching points. Overexpression of B23 promotes axon growth with abundant branching points in growing hippocampal neurons, but depletion of B23 impairs axon growth, leading to neuronal death. Following injury to the trisynaptic path in hippocampal slice, overexpression of B23 remarkably increased the number and length of regenerative fibers in the mossy fiber path. Our study suggests that B23 expression in developing neurons is essential for neuritogenesis and axon growth and that up-regulation of B23 may be a strategy for enhancing the reconstitution of synaptic paths after injury to hippocampal synapses.
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Affiliation(s)
- Taegwan Yun
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea; Single Cell Network Research Center, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Hyo Rim Ko
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea; Single Cell Network Research Center, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Jaeyoung Ahn
- Department of Medicine, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Eun-Ju Jin
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea; Single Cell Network Research Center, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Jung Min Jo
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Il-Sun Kwon
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea
| | - Sung-Woo Cho
- Department of Biochemistry and Molecular Biology, University of Ulsan, College of Medicine, Seoul, 05505, South Korea
| | - Yun Sil Chang
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, and Department of Health Sciences and Technology, SAIHST, Sungkyunkwan University, South Korea; Stem Cell & Regenerative Medicine Institute, Samsung Medical Center, Seoul, 06351, South Korea
| | - Won Soon Park
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, and Department of Health Sciences and Technology, SAIHST, Sungkyunkwan University, South Korea; Stem Cell & Regenerative Medicine Institute, Samsung Medical Center, Seoul, 06351, South Korea.
| | - Jee-Yin Ahn
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea; Single Cell Network Research Center, Sungkyunkwan University School of Medicine, Suwon, 16419, South Korea; Samsung Biomedical Research Institute, Samsung Medical Center, Seoul, 06351, South Korea.
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3
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Fuschini G, Cotrufo T, Ros O, Muhaisen A, Andrés R, Comella JX, Soriano E. Syntaxin-1/TI-VAMP SNAREs interact with Trk receptors and are required for neurotrophin-dependent outgrowth. Oncotarget 2018; 9:35922-35940. [PMID: 30542508 PMCID: PMC6267591 DOI: 10.18632/oncotarget.26307] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 10/24/2018] [Indexed: 01/19/2023] Open
Abstract
SNARE proteins are essential components of the machinery that regulates vesicle trafficking and exocytosis. Their role is critical for the membrane-fusion processes that occur during neurotransmitter release. However, research in the last decade has also unraveled the relevance of these proteins in membrane expansion and cytoskeletal rearrangements during developmental processes such as neuronal migration and growth cone extension and attraction. Neurotrophins are neurotrophic factors that are required for many cellular functions throughout the brain, including neurite outgrowth and guidance, synaptic formation, and plasticity. Here we show that neurotrophin Trk receptors form a specific protein complex with the t-SNARE protein Syntaxin 1, both in vivo and in vitro. We also demonstrate that blockade of Syntaxin 1 abolishes neurotrophin-dependent growth of axons in neuronal cultures and decreases exocytotic events at the tip of axonal growth cones. 25-kDa soluble N-ethylmaleimide-sensitive factor attachment protein and Vesicle-associated membrane protein 2 do not participate in the formation of this SNARE complex, while tetanus neurotoxin-insensitive vesicle-associated membrane protein interacts with Trk receptors; knockdown of this (v) SNARE impairs Trk-dependent outgrowth. Taken together, our results support the notion that an atypical SNARE complex comprising Syntaxin 1 and tetanus neurotoxin-insensitive vesicle-associated membrane protein is required for axonal neurotrophin function.
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Affiliation(s)
- Giulia Fuschini
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
| | - Tiziana Cotrufo
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
- Vall d'Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
| | - Oriol Ros
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
| | - Ashraf Muhaisen
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Vall d'Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
| | - Rosa Andrés
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
| | - Joan X. Comella
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
- Vall d'Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
| | - Eduardo Soriano
- Department of Cell Biology, Physiology and Immunology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28031 Madrid, Spain
- Vall d'Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
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Ren Y, Mlodzianoski MJ, Lee AC, Huang F, Suter DM. A low-cost microwell device for high-resolution imaging of neurite outgrowth in 3D. J Neural Eng 2018; 15:035001. [PMID: 29363623 DOI: 10.1088/1741-2552/aaaa32] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
OBJECTIVE Current neuronal cell culture is mostly performed on two-dimensional (2D) surfaces, which lack many of the important features of the native environment of neurons, including topographical cues, deformable extracellular matrix, and spatial isotropy or anisotropy in three dimensions. Although three-dimensional (3D) cell culture systems provide a more physiologically relevant environment than 2D systems, their popularity is greatly hampered by the lack of easy-to-make-and-use devices. We aim to develop a widely applicable 3D culture procedure to facilitate the transition of neuronal cultures from 2D to 3D. APPROACH We made a simple microwell device for 3D neuronal cell culture that is inexpensive, easy to assemble, and fully compatible with commonly used imaging techniques, including super-resolution microscopy. MAIN RESULTS We developed a novel gel mixture to support 3D neurite regeneration of Aplysia bag cell neurons, a system that has been extensively used for quantitative analysis of growth cone dynamics in 2D. We found that the morphology and growth pattern of bag cell growth cones in 3D culture closely resemble the ones of growth cones observed in vivo. We demonstrated the capability of our device for high-resolution imaging of cytoskeletal and signaling proteins as well as organelles. SIGNIFICANCE Neuronal cell culture has been a valuable tool for neuroscientists to study the behavior of neurons in a controlled environment. Compared to 2D, neurons cultured in 3D retain the majority of their native characteristics, while offering higher accessibility, control, and repeatability. We expect that our microwell device will facilitate a wider adoption of 3D neuronal cultures to study the mechanisms of neurite regeneration.
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Affiliation(s)
- Yuan Ren
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, United States of America
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5
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Yao L, Li Y. The Role of Direct Current Electric Field-Guided Stem Cell Migration in Neural Regeneration. Stem Cell Rev Rep 2017; 12:365-75. [PMID: 27108005 DOI: 10.1007/s12015-016-9654-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Effective directional axonal growth and neural cell migration are crucial in the neural regeneration of the central nervous system (CNS). Endogenous currents have been detected in many developing nervous systems. Experiments have demonstrated that applied direct current (DC) electric fields (EFs) can guide axonal growth in vitro, and attempts have been made to enhance the regrowth of damaged spinal cord axons using DC EFs in in vivo experiments. Recent work has revealed that the migration of stem cells and stem cell-derived neural cells can be guided by DC EFs. These studies have raised the possibility that endogenous and applied DC EFs can be used to direct neural tissue regeneration. Although the mechanism of EF-directed axonal growth and cell migration has not been fully understood, studies have shown that the polarization of cell membrane proteins and the activation of intracellular signaling molecules are involved in the process. The application of EFs is a promising biotechnology for regeneration of the CNS.
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Affiliation(s)
- Li Yao
- Department of Biological Sciences, Wichita State University, Wichita, KS, 67260, USA.
| | - Yongchao Li
- Department of Biological Sciences, Wichita State University, Wichita, KS, 67260, USA
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Ko HR, Kwon IS, Hwang I, Jin EJ, Shin JH, Brennan-Minnella AM, Swanson R, Cho SW, Lee KH, Ahn JY. Akt1-Inhibitor of DNA binding2 is essential for growth cone formation and axon growth and promotes central nervous system axon regeneration. eLife 2016; 5. [PMID: 27938661 PMCID: PMC5153247 DOI: 10.7554/elife.20799] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Accepted: 11/28/2016] [Indexed: 02/02/2023] Open
Abstract
Mechanistic studies of axon growth during development are beneficial to the search for neuron-intrinsic regulators of axon regeneration. Here, we discovered that, in the developing neuron from rat, Akt signaling regulates axon growth and growth cone formation through phosphorylation of serine 14 (S14) on Inhibitor of DNA binding 2 (Id2). This enhances Id2 protein stability by means of escape from proteasomal degradation, and steers its localization to the growth cone, where Id2 interacts with radixin that is critical for growth cone formation. Knockdown of Id2, or abrogation of Id2 phosphorylation at S14, greatly impairs axon growth and the architecture of growth cone. Intriguingly, reinstatement of Akt/Id2 signaling after injury in mouse hippocampal slices redeemed growth promoting ability, leading to obvious axon regeneration. Our results suggest that Akt/Id2 signaling is a key module for growth cone formation and axon growth, and its augmentation plays a potential role in CNS axonal regeneration. DOI:http://dx.doi.org/10.7554/eLife.20799.001
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Affiliation(s)
- Hyo Rim Ko
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Il-Sun Kwon
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Inwoo Hwang
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Eun-Ju Jin
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Joo-Ho Shin
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Angela M Brennan-Minnella
- The Department of Neurology, University of California, San Francisco Medical Center, San Francisco, United States
| | - Raymond Swanson
- The Department of Neurology, University of California, San Francisco Medical Center, San Francisco, United States
| | - Sung-Woo Cho
- Department of Biochemistry and Molecular Biology, University of Ulsan, College of Medicine, Seoul, Republic of Korea
| | - Kyung-Hoon Lee
- Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Department of Anatomy, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
| | - Jee-Yin Ahn
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.,Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
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7
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Rappaz B, Lai Wing Sun K, Correia JP, Wiseman PW, Kennedy TE. FLIM FRET Visualization of Cdc42 Activation by Netrin-1 in Embryonic Spinal Commissural Neuron Growth Cones. PLoS One 2016; 11:e0159405. [PMID: 27482713 PMCID: PMC4970703 DOI: 10.1371/journal.pone.0159405] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 07/02/2016] [Indexed: 12/29/2022] Open
Abstract
Netrin-1 is an essential extracellular chemoattractant that signals through its receptor DCC to guide commissural axon extension in the embryonic spinal cord. DCC directs the organization of F-actin in growth cones by activating an intracellular protein complex that includes the Rho GTPase Cdc42, a critical regulator of cell polarity and directional migration. To address the spatial distribution of signaling events downstream of netrin-1, we expressed the FRET biosensor Raichu-Cdc42 in cultured embryonic rat spinal commissural neurons. Using FLIM-FRET imaging we detected rapid activation of Cdc42 in neuronal growth cones following application of netrin-1. Investigating the signaling mechanisms that control Cdc42 activation by netrin-1, we demonstrate that netrin-1 rapidly enriches DCC at the leading edge of commissural neuron growth cones and that netrin-1 induced activation of Cdc42 in the growth cone is blocked by inhibiting src family kinase signaling. These findings reveal the activation of Cdc42 in embryonic spinal commissural axon growth cones and support the conclusion that src family kinase activation downstream of DCC is required for Cdc42 activation by netrin-1.
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Affiliation(s)
- Benjamin Rappaz
- Program in NeuroEngineering, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Physics, McGill University, Montreal, QC, H3A 2T8, Canada
| | - Karen Lai Wing Sun
- Program in NeuroEngineering, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montreal, QC, H3A 2B4, Canada
| | - James P. Correia
- Program in NeuroEngineering, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montreal, QC, H3A 2B4, Canada
| | - Paul W. Wiseman
- Program in NeuroEngineering, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Physics, McGill University, Montreal, QC, H3A 2T8, Canada
- Department of Chemistry, McGill University, Montreal, QC, H3A 0B8, Canada
| | - Timothy E. Kennedy
- Program in NeuroEngineering, McGill University, Montreal, QC, H3A 2B4, Canada
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montreal, QC, H3A 2B4, Canada
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8
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Cammarata GM, Bearce EA, Lowery LA. Cytoskeletal social networking in the growth cone: How +TIPs mediate microtubule-actin cross-linking to drive axon outgrowth and guidance. Cytoskeleton (Hoboken) 2016; 73:461-76. [PMID: 26783725 DOI: 10.1002/cm.21272] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/08/2016] [Accepted: 01/08/2016] [Indexed: 11/08/2022]
Abstract
The growth cone is a unique structure capable of guiding axons to their proper destinations. Within the growth cone, extracellular guidance cues are interpreted and then transduced into physical changes in the actin filament (F-actin) and microtubule cytoskeletons, providing direction and movement. While both cytoskeletal networks individually possess important growth cone-specific functions, recent data over the past several years point towards a more cooperative role between the two systems. Facilitating this interaction between F-actin and microtubules, microtubule plus-end tracking proteins (+TIPs) have been shown to link the two cytoskeletons together. Evidence suggests that many +TIPs can couple microtubules to F-actin dynamics, supporting both microtubule advance and retraction in the growth cone periphery. In addition, growing in vitro and in vivo data support a secondary role for +TIPs in which they may participate as F-actin nucleators, thus directly influencing F-actin dynamics and organization. This review focuses on how +TIPs may link F-actin and microtubules together in the growth cone, and how these interactions may influence axon guidance. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
| | | | - Laura Anne Lowery
- Department of Biology, Boston College, Chestnut Hill, Massachusetts.
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9
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Low Density Lipoprotein Receptor Related Proteins as Regulators of Neural Stem and Progenitor Cell Function. Stem Cells Int 2016; 2016:2108495. [PMID: 26949399 PMCID: PMC4754494 DOI: 10.1155/2016/2108495] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 11/24/2015] [Accepted: 01/06/2016] [Indexed: 12/20/2022] Open
Abstract
The central nervous system (CNS) is a highly organised structure. Many signalling systems work in concert to ensure that neural stem cells are appropriately directed to generate progenitor cells, which in turn mature into functional cell types including projection neurons, interneurons, astrocytes, and oligodendrocytes. Herein we explore the role of the low density lipoprotein (LDL) receptor family, in particular family members LRP1 and LRP2, in regulating the behaviour of neural stem and progenitor cells during development and adulthood. The ability of LRP1 and LRP2 to bind a diverse and extensive range of ligands, regulate ligand endocytosis, recruit nonreceptor tyrosine kinases for direct signal transduction and signal in conjunction with other receptors, enables them to modulate many crucial neural cell functions.
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10
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Smirnova L, Harris G, Delp J, Valadares M, Pamies D, Hogberg HT, Waldmann T, Leist M, Hartung T. A LUHMES 3D dopaminergic neuronal model for neurotoxicity testing allowing long-term exposure and cellular resilience analysis. Arch Toxicol 2015; 90:2725-2743. [PMID: 26647301 PMCID: PMC5065586 DOI: 10.1007/s00204-015-1637-z] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Accepted: 11/09/2015] [Indexed: 12/21/2022]
Abstract
Several shortcomings of current Parkinson’s disease (PD) models limit progress in identification of environmental contributions to disease pathogenesis. The conditionally immortalized cell line LUHMES promises to make human dopaminergic neuronal cultures more easily available, but these cells are difficult to culture for extended periods of time. We overcame this problem by culturing them in 3D with minor medium modifications. The 3D neuronal aggregates allowed penetration by small molecules and sufficient oxygen and nutrient supply for survival of the innermost cells. Using confocal microscopy, gene expression, and flow cytometry, we characterized the 3D model and observed a highly reproducible differentiation process. Visualization and quantification of neurites in aggregates was achieved by adding 2 % red fluorescent protein-transfected LUHMES cells. The mitochondrial toxicants and established experimental PD agents, rotenone and MPP+, perturbed genes involved in one-carbon metabolism and transsulfuration pathways (ASS1, CTH, and SHTM2) as in 2D cultures. We showed, for the first time in LUHMES, down-regulation of mir-7, a miRNA known to target alpha-synuclein and to be involved in PD. This was observed as early as 12 h after rotenone exposure, when pro-apoptotic mir-16 and rotenone-sensitive mir-210 were not yet significantly perturbed. Finally, washout experiments demonstrated that withdrawal of rotenone led to counter-regulation of mir-7 and ASS1, CTH, and SHTM2 genes. This suggests a possible role of these genes in direct cellular response to the toxicant, and the model appears to be suitable to address the processes of resilience and recovery in neurotoxicology and Parkinson’s disease in future studies.
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Affiliation(s)
- L Smirnova
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA.
| | - G Harris
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
| | - J Delp
- Center for Alternatives to Animal Testing (CAAT), Department of Biology, University of Konstanz, Konstanz, Germany
| | - M Valadares
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
| | - D Pamies
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
| | - H T Hogberg
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
| | - T Waldmann
- Center for Alternatives to Animal Testing (CAAT), Department of Biology, University of Konstanz, Konstanz, Germany
| | - M Leist
- Center for Alternatives to Animal Testing (CAAT), Department of Biology, University of Konstanz, Konstanz, Germany
| | - T Hartung
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
- Center for Alternatives to Animal Testing (CAAT), Department of Biology, University of Konstanz, Konstanz, Germany
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11
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Tamariz E, Varela-Echavarría A. The discovery of the growth cone and its influence on the study of axon guidance. Front Neuroanat 2015; 9:51. [PMID: 26029056 PMCID: PMC4432662 DOI: 10.3389/fnana.2015.00051] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Accepted: 04/13/2015] [Indexed: 11/25/2022] Open
Abstract
For over a century, there has been a great deal of interest in understanding how neural connectivity is established during development and regeneration. Interest in the latter arises from the possibility that knowledge of this process can be used to re-establish lost connections after lesion or neurodegeneration. At the end of the XIX century, Santiago Ramón y Cajal discovered that the distal tip of growing axons contained a structure that he called the growth cone. He proposed that this structure enabled the axon's oriented growth in response to attractants, now known as chemotropic molecules. He further proposed that the physical properties of the surrounding tissues could influence the growth cone and the direction of growth. This seminal discovery afforded a plausible explanation for directed axonal growth and has led to the discovery of axon guidance mechanisms that include diffusible attractants and repellants and guidance cues anchored to cell membranes or extracellular matrix. In this review the major events in the development of this field are discussed.
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Affiliation(s)
- Elisa Tamariz
- Instituto de Ciencias de la Salud, Universidad VeracruzanaXalapa, Mexico
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12
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Abstract
The p21 activated kinases (Paks) are well known effector proteins for the Rho GTPases Cdc42 and Rac. The Paks contain 6 members, which fall into 2 families of proteins. The first family consists of Paks 1, 2, and 3, and the second consists of Paks 4, 5, and 6. While some of the Paks are ubiquitously expressed, others have more restrictive tissue specificity. All of them are found in the nervous system. Studies using cell culture, transgenic mice, and knockout mice, have revealed important roles for the Paks in cytoskeletal organization and in many aspects of cell growth and development. This review discusses the basic structures of the Paks, and their roles in cell growth, development, and in cancer.
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Affiliation(s)
- Chetan K Rane
- Susan Lehman Cullman Laboratory for Cancer Research; Department of Chemical Biology; Ernest Mario School of Pharmacy; Rutgers The State University of New Jersey; Piscataway, NJ USA
| | - Audrey Minden
- Susan Lehman Cullman Laboratory for Cancer Research; Department of Chemical Biology; Ernest Mario School of Pharmacy; Rutgers The State University of New Jersey; Piscataway, NJ USA
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13
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Zeng J, Huang Z, Yin G, Qin J, Chen X, Gu J. Fabrication of conductive NGF-conjugated polypyrrole–poly(l-lactic acid) fibers and their effect on neurite outgrowth. Colloids Surf B Biointerfaces 2013; 110:450-7. [DOI: 10.1016/j.colsurfb.2013.05.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 04/15/2013] [Accepted: 05/08/2013] [Indexed: 12/28/2022]
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Gallo G. Mechanisms underlying the initiation and dynamics of neuronal filopodia: from neurite formation to synaptogenesis. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 301:95-156. [PMID: 23317818 DOI: 10.1016/b978-0-12-407704-1.00003-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Filopodia are finger-like cellular protrusions found throughout the metazoan kingdom and perform fundamental cellular functions during development and cell migration. Neurons exhibit a wide variety of extremely complex morphologies. In the nervous system, filopodia underlie many major morphogenetic events. Filopodia have roles spanning the initiation and guidance of neuronal processes, axons and dendrites to the formation of synaptic connections. This chapter addresses the mechanisms of the formation and dynamics of neuronal filopodia. Some of the major lessons learned from the study of neuronal filopodia are (1) there are multiple mechanisms that can regulate filopodia in a context-dependent manner, (2) that filopodia are specialized subcellular domains, (3) that filopodia exhibit dynamic membrane recycling which also controls aspects of filopodial dynamics, (4) that neuronal filopodia contain machinery for the orchestration of the actin and microtubule cytoskeleton, and (5) localized protein synthesis contributes to neuronal filopodial dynamics.
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Affiliation(s)
- Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Center for Neural Repair and Rehabilitation, Department of Anatomy and Cell Biology, Temple University, Philadelphia, PA, USA.
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15
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Morita S, Miyata S. Synaptic localization of growth-associated protein 43 in cultured hippocampal neurons during synaptogenesis. Cell Biochem Funct 2012; 31:400-11. [PMID: 23055398 DOI: 10.1002/cbf.2914] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2012] [Revised: 09/11/2012] [Accepted: 09/12/2012] [Indexed: 11/07/2022]
Abstract
Growth-associated protein 43 (GAP-43), a novel axonal phosphoprotein, is originally identified as a growth-cone-specific protein of developing neurons in vitro. The expression of GAP-43 is also shown to be up-regulated concomitant with increased synaptic plasticity in the brains in vivo, but how GAP-43 is concerned with synaptic plasticity is not well understood. In the present study, therefore, we aimed to elucidate subcellular localization of GAP-43 as culture development of rat hippocampal neurons. Western blotting showed that the expression of GAP-43 in the cerebral and hippocampal tissues was prominently high at postnatal days 14 and 21 or the active period of synaptogenesis. Double-labelling immunohistochemistry with an axonal marker Tau revealed that the immunoreactivity of GAP-43 was seen throughout axons of cultured hippocampal neurons but stronger at axonal puncta of developing neurons than axonal processes. Double-labelling immunohistochemistry with presynaptic terminal markers of synapsin and synaptotagmin revealed that the immunoreactivity of GAP-43 was observed mostly at weak synapsin- and synaptotagmin-positive puncta rather than strong ones. The quantitative analysis of immunofluorescent intensity showed a clear inverse correlation between GAP-43 and either synapsin or synaptotagmin expression. These data indicate that GAP-43 is highly expressed at immature growing axonal terminals and its expression is decreased along with the maturation of synaptogenesis.
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Affiliation(s)
- Shoko Morita
- Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
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16
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Jean DC, Baas PW, Black MM. A novel role for doublecortin and doublecortin-like kinase in regulating growth cone microtubules. Hum Mol Genet 2012; 21:5511-27. [PMID: 23001563 DOI: 10.1093/hmg/dds395] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Doublecortin (DCX) and doublecortin-like kinase (DCLK), closely related family members, are microtubule-associated proteins with overlapping functions in both neuronal migration and axonal outgrowth. In growing axons, these proteins appear to have their primary functions in the growth cone. Here, we used siRNA to deplete these proteins from cultured rat sympathetic neurons. Normally, microtubules in the growth cone exhibit a gently curved contour as they extend from the base of the cone toward its periphery. However, following depletion of DCX and DCLK, microtubules throughout the growth cone become much more curvy, with many microtubules exhibiting multiple prominent bends over relatively short distances, creating a configuration that we termed wave-like folds. Microtubules with these folds appeared as if they were buckling in response to powerful forces. Indeed, inhibition of myosin-II, which generates forces on the actin cytoskeleton to push microtubules in the growth cone back toward the axonal shaft, significantly decreases the frequency of these wave-like folds. In addition, in the absence of DCX and DCLK, the depth of microtubule invasion into filopodia is reduced compared with controls, and at a functional level, growth cone responses to substrate guidance cues are altered. Conversely, overexpression of DCX results in microtubules that are straighter than usual, suggesting that higher levels of these proteins can enable an even greater resistance to folding. These findings support a role for DCX and DCLK in enabling microtubules to overcome retrograde actin-based forces, thereby facilitating the ability of the growth cone to carry out its crucial path-finding functions.
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Affiliation(s)
- Daphney C Jean
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA
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17
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Vitriol EA, Zheng JQ. Growth cone travel in space and time: the cellular ensemble of cytoskeleton, adhesion, and membrane. Neuron 2012; 73:1068-81. [PMID: 22445336 DOI: 10.1016/j.neuron.2012.03.005] [Citation(s) in RCA: 174] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/05/2012] [Indexed: 10/28/2022]
Abstract
Growth cones, found at the tip of axonal projections, are the sensory and motile organelles of developing neurons that enable axon pathfinding and target recognition for precise wiring of the neural circuitry. To date, many families of conserved guidance molecules and their corresponding receptors have been identified that work in space and time to ensure billions of axons to reach their targets. Research in the past two decades has also gained significant insight into the ways in which growth cones translate extracellular signals into directional migration. This review aims to examine new progress toward understanding the cellular mechanisms underlying directional motility of the growth cone and to discuss questions that remain to be addressed. Specifically, we will focus on the cellular ensemble of cytoskeleton, adhesion, and membrane and examine how the intricate interplay between these processes orchestrates the directed movement of growth cones.
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Affiliation(s)
- Eric A Vitriol
- Department of Cell Biology and Neurology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA
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18
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Myers JP, Robles E, Ducharme-Smith A, Gomez TM. Focal adhesion kinase modulates Cdc42 activity downstream of positive and negative axon guidance cues. J Cell Sci 2012; 125:2918-29. [PMID: 22393238 DOI: 10.1242/jcs.100107] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
There is biochemical, imaging and functional evidence that Rho GTPase signaling is a crucial regulator of actin-based structures such as lamellipodia and filopodia. However, although Rho GTPases are believed to serve similar functions in growth cones, the spatiotemporal dynamics of Rho GTPase signaling has not been examined in living growth cones in response to known axon guidance cues. Here we provide the first measurements of Cdc42 activity in living growth cones acutely stimulated with both growth-promoting and growth-inhibiting axon-guidance cues. Interestingly, we find that both permissive and repulsive factors can work by modulating Cdc42 activity, but in opposite directions. We find that the growth-promoting factors laminin and BDNF activate Cdc42, whereas the inhibitor Slit2 reduces Cdc42 activity in growth cones. Remarkably, we find that regulation of focal adhesion kinase (FAK) activity is a common upstream modulator of Cdc42 by BDNF, laminin and Slit. These findings suggest that rapid modulation of Cdc42 signaling through FAK by receptor activation underlies changes in growth cone motility in response to permissive and repulsive guidance cues.
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Affiliation(s)
- Jonathan P Myers
- Department of Neuroscience, Medical Scientist Training Program and Neuroscience Training Program, University of Wisconsin, Madison, WI 53706, USA
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19
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Yao L, Pandit A, Yao S, McCaig CD. Electric field-guided neuron migration: a novel approach in neurogenesis. TISSUE ENGINEERING PART B-REVIEWS 2011; 17:143-53. [PMID: 21275787 DOI: 10.1089/ten.teb.2010.0561] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Effective directional neuron migration is crucial in development of the central nervous system and for neurogenesis. Endogenous electrical signals are present in many developing systems and crucial cellular behaviors such as neuronal cell division, cell migration, and cell differentiation are all under the influence of such endogenous electrical cues. Preclinical in vivo studies have used electric fields (EFs) to attempt to enhance regrowth of damaged spinal cord axons with some success. Recent evidence shows that small EFs not only guide axonal growth, but also direct the earlier events of neuronal migration and neuronal cell division. This raises the possibility that applied or endogenous EFs, perhaps in combination, may direct transplanted neural stem cells, or regenerating neurons, to the desired site after brain injury or neuron degeneration. The high complexity of both structure and function of the nervous system, however, poses significant challenges to techniques for applying EFs to promote neurogenesis. The evolution of functional biomaterials and nanotechnology may provide promising solutions for the application of EFs in guiding neuron migration and neurogenesis within the central nervous system.
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Affiliation(s)
- Li Yao
- Network of Excellence for Functional Biomaterials, National Center for Biomedical Engineering Science, National University of Ireland, Galway, Ireland
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20
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Buel GR, Rush J, Ballif BA. Fyn promotes phosphorylation of collapsin response mediator protein 1 at tyrosine 504, a novel, isoform-specific regulatory site. J Cell Biochem 2011; 111:20-8. [PMID: 20506281 DOI: 10.1002/jcb.22659] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In vertebrates the collapsin response mediator proteins (CRMPs) are encoded by five highly related genes. CRMPs are cytosolic phosphoproteins abundantly expressed in developing and mature mammalian brains. CRMPs are best understood as effectors of Semaphorin 3A signaling regulating growth cone collapse in migratory neurons. Phosphorylation in the carboxyl-terminal regulatory domain of CRMPs by several serine/threonine kinases has been described. These phoshorylation events appear to function, at least in part, to disrupt the interaction of CRMPs with tubulin heterodimers. In a large-scale phosphoproteomic analysis of murine brain, we recently identified a number of in vivo tyrosine phosphorylation sites on CRMP isoforms. Using biochemical approaches and quantitative mass spectrometry we demonstrate that one of these sites, CRMP1 tyrosine 504 (Y504), is a primary target of the Src family of tyrosine kinases (SFKs), specifically Fyn. Y504 is adjacent to CDK5 and GSK-3beta sites that regulate the interaction of CRMPs with tubulin. Although Y504 is highly conserved among vertebrate CRMP1 orthologs, a residue corresponding to Y504 is absent in CRMP isoforms 2-5. This suggests an isoform-specific regulatory role for CRMP1 Y504 phosphorylation and may help explain the observation that CRMP1-deficient mice exhibit neuronal migration defects not compensated for by CRMPs 2-5.
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Affiliation(s)
- Gwen R Buel
- Department of Biology, University of Vermont, 120A Marsh Life Science Building, 109 Carrigan Drive, Burlington, Vermont 05405, USA
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21
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Marsick BM, Flynn KC, Santiago-Medina M, Bamburg JR, Letourneau PC. Activation of ADF/cofilin mediates attractive growth cone turning toward nerve growth factor and netrin-1. Dev Neurobiol 2010; 70:565-88. [PMID: 20506164 DOI: 10.1002/dneu.20800] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Proper neural circuitry requires that growth cones, motile tips of extending axons, respond to molecular guidance cues expressed in the developing organism. However, it is unclear how guidance cues modify the cytoskeleton to guide growth cone pathfinding. Here, we show acute treatment with two attractive guidance cues, nerve growth factor (NGF) and netrin-1, for embryonic dorsal root ganglion and temporal retinal neurons, respectively, results in increased growth cone membrane protrusion, actin polymerization, and filamentous actin (F-actin). ADF/cofilin (AC) family proteins facilitate F-actin dynamics, and we found the inactive phosphorylated form of AC is decreased in NGF- or netrin-1-treated growth cones. Directly increasing AC activity mimics addition of NGF or netrin-1 to increase growth cone protrusion and F-actin levels. Extracellular gradients of NGF, netrin-1, and a cell-permeable AC elicit attractive growth cone turning and increased F-actin barbed ends, F-actin accumulation, and active AC in growth cone regions proximal to the gradient source. Reducing AC activity blunts turning responses to NGF and netrin. Our results suggest that gradients of NGF and netrin-1 locally activate AC to promote actin polymerization and subsequent growth cone turning toward the side containing higher AC activity.
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Affiliation(s)
- Bonnie M Marsick
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA
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22
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Ahmed El-Said W, Yea CH, Jung M, Kim H, Choi JW. Analysis of effect of nanoporous alumina substrate coated with polypyrrole nanowire on cell morphology based on AFM topography. Ultramicroscopy 2010; 110:676-81. [DOI: 10.1016/j.ultramic.2010.02.031] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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23
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Watanabe TM, Tokuo H, Gonda K, Higuchi H, Ikebe M. Myosin-X induces filopodia by multiple elongation mechanism. J Biol Chem 2010; 285:19605-14. [PMID: 20392702 DOI: 10.1074/jbc.m109.093864] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Filopodia are actin-rich finger-like cytoplasmic projections extending from the leading edge of cells. Unconventional myosin-X is involved in the protrusion of filopodia. However, the underlying mechanism of myosin-X-induced filopodia formation is obscure. Here, we studied the movements of myosin-X during filopodia protrusion using a total internal reflection microscope to clarify the mechanism of myosin-X-induced filopodia formation. Myosin-X was recruited to the discrete site at the leading edge where it assembles with exponential kinetics before the filopodia extension. The myosin-X-induced filopodia showed repeated extension-retraction cycles with each extension of 2.4 microm, which was critical to produce long filopodia. Myosin-X, lacking the FERM domain, could move to the tip as does the wild type. However, it was transported toward the cell body during filopodia retraction, did not undergo multiple extension-retraction cycles, and failed to produce long filopodia. During the filopodia protrusion, the single molecules of full-length myosin-X moved within filopodia. The majority of the fluorescence spots showed two-step photobleaching, suggesting that the moving myosin-X is a dimer. Deletion of the FERM domain did not change the movement at the single molecule level with the same velocity of approximately 600 nm/s as wild-type, suggesting that the myosin-X in filopodia moves without interaction with the attached membrane via the FERM domain. Based upon these results, we have proposed a model of myosin-X-induced filopodia protrusion.
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Affiliation(s)
- Tomonobu M Watanabe
- World Premier International Research Center Initiative, Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan
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24
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An essential role of the aPKC-Aurora A-NDEL1 pathway in neurite elongation by modulation of microtubule dynamics. Nat Cell Biol 2009; 11:1057-68. [PMID: 19668197 DOI: 10.1038/ncb1919] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Accepted: 06/19/2009] [Indexed: 11/08/2022]
Abstract
Orchestrated remodelling of the cytoskeketon is prominent during neurite extension. In contrast with the extensive characterization of actin filament regulation, little is known about the dynamics of microtubules during neurite extension. Here we identify an atypical protein kinase C (aPKC)-Aurora A-NDEL1 pathway that is crucial for the regulation of microtubule organization during neurite extension. aPKC phosphorylates Aurora A at Thr 287 (T287), which augments interaction with TPX2 and facilitates activation of Aurora A at the neurite hillock, followed by phosphorylation of NDEL1 at S251 and recruitment. Suppression of aPKC, Aurora A or TPX2, or disruption of Ndel1, results in severe impairment of neurite extension. Analysis of microtubule dynamics with a microtubule plus-end marker revealed that suppression of the aPKC-Aurora A-NDEL1 pathway resulted in a significant decrease in the frequency of microtubule emanation from the microtubule organizing centre (MTOC), suggesting that Aurora A acts downstream of aPKC. These findings demonstrate a surprising role of aPKC-Aurora A-NDEL1 pathway in microtubule remodelling during neurite extension.
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25
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Mingorance-Le Meur A, Mohebiany AN, O'Connor TP. Varicones and growth cones: two neurite terminals in PC12 cells. PLoS One 2009; 4:e4334. [PMID: 19183810 PMCID: PMC2629561 DOI: 10.1371/journal.pone.0004334] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Accepted: 12/19/2008] [Indexed: 11/19/2022] Open
Abstract
The rat adrenal pheochromocytoma PC12 cell line is one of the traditional models for the study of neurite outgrowth and growth cone behavior. To clarify to what extent PC12 neurite terminals can be compared to neuronal growth cones, we have analyzed their morphology and protein distribution in fixed PC12 cells by immunocytochemistry. Our results show that that PC12 cells display a special kind of neurite terminal that includes a varicosity in close association with a growth cone. This hybrid terminal, or "varicone", is characterized by the expression of specific markers not typically present in neuronal growth cones. For example, we show that calpain-2 is a specific marker of varicones and can be detected even before the neurite develops. Our data also shows that a fraction of PC12 neurites end in regular growth cones, which we have compared to hippocampal neurites as a control. We also report the extraordinary incidence of varicones in the literature referred to as "growth cones". In summary, we provide evidence of two different kinds of neurite terminals in PC12 cells, including a PC12-specific terminal, which implies that care must be taken when using them as a model for neuronal growth cones or neurite outgrowth.
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Affiliation(s)
- Ana Mingorance-Le Meur
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada.
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26
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Abstract
Actin filaments are thin polymers of the 42 kD protein actin. In mature axons a network of subaxolemmal actin filaments provide stability for membrane integrity and a substrate for short distance transport of cargos. In developing neurons dynamic regulation of actin polymerization and organization mediates axonal morphogenesis and axonal pathfinding to synaptic targets. Other changes in axonal shape, collateral branching, branch retraction, and axonal regeneration, also depend on actin filament dynamics. Actin filament organization is regulated by a diversity of actin-binding proteins (ABP). ABP are the focus of complex extrinsic and intrinsic signaling pathways, and many neurological pathologies and dysfunctions arise from defective regulation of ABP function.
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Affiliation(s)
- Paul C Letourneau
- Department of Neuroscience, 6-145 Jackson Hall, University of Minnesota, Minneapolis, MN 55455, USA.
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27
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Computational model provides insight into the distinct responses of neurons to chemical and topographical cues. Ann Biomed Eng 2008; 37:363-74. [PMID: 19067167 DOI: 10.1007/s10439-008-9613-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 11/24/2008] [Indexed: 11/27/2022]
Abstract
Neuronal cell polarization (i.e., establishment of an axon) and axon guidance are mediated and controlled by mechanical and chemical signals from the environment. Unfortunately, an integrated approach to study cell-substrate interactions in a unified framework incorporating structural and chemical effects of the substrate has been lacking. In this paper, we present a new model combining experimental and computational methods to better understand the distinct behavior of E18 hippocampal neurons in response to topographical vs. immobilized chemical cues. We present results from our coarse-grain physiological computational model that correctly describes previously observed phenomena and predicts behavior that was subsequently tested through new experiments. The model differentiates topographical from chemical cues via a difference in cue spacing in these two substrates. Using the feature size spacing for topographical cues and a minimum step size, governed by the physics of filopodia protrusion, for chemical cues, the model successfully mimics the trend observed in experimental polarization probability for four different topographical feature sizes and constant chemical cue spacing. Our results not only show good agreement with experiments, but also provide novel suggestions for development of substrates for finer control of neuronal cell polarization.
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28
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Ruff RL, McKerracher L, Selzer ME. Repair and Neurorehabilitation Strategies for Spinal Cord Injury. Ann N Y Acad Sci 2008; 1142:1-20. [DOI: 10.1196/annals.1444.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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29
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Fonner JM, Forciniti L, Nguyen H, Byrne JD, Kou YF, Syeda-Nawaz J, Schmidt CE. Biocompatibility implications of polypyrrole synthesis techniques. Biomed Mater 2008; 3:034124. [PMID: 18765899 DOI: 10.1088/1748-6041/3/3/034124] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Polypyrrole (PPy) is an inherently conducting polymer that has shown great promise for biomedical applications within the nervous system. However, to effectively use PPy as a biomaterial implant, it is important to understand and reproducibly control the electrical properties, physical topography and surface chemistry of the polymer. Although there is much research published on the use of PPy in various applications, there is no systematic study linking the methodologies used for PPy synthesis to PPy's basic polymeric properties (e.g., hydrophilicity, surface roughness), and to the biological effects these properties have on cells. Electrochemically synthesized PPy films differ greatly in their characteristics depending on synthesis parameters such as dopant, substrate and thickness, among other parameters. In these studies, we have used three dopants (chloride (Cl), tosylate (ToS), polystyrene sulfonate (PSS)), two substrates (gold and indium tin oxide-coated glass), and a range of thicknesses, to measure and compare the biomedically important characteristics of surface roughness, contact angle, conductivity, dopant stability and cell adhesion (using PC-12 cells and Schwann cells). As predicted, we discovered large differences in roughness depending on the dopant used and the thickness of the film, while substrate choice had little effect. From contact angle measurements, PSS was found to yield the most hydrophilic material, most likely because of free charges from the long PSS chains exposed on the surface of the PPy. ToS-doped PPy films were tenfold more conductive than Cl- or PSS-doped films. X-ray photoelectron spectroscopy studies were used to evaluate dopant concentrations of PPy films stored in water and phosphate buffered saline over 14 days, and conductance studies over the same timeframe measured electrical stability. PSS proved to be the most stable dopant, though all films experienced significant decay in conductivity and dopant concentration. Cell adhesion studies demonstrated the dependence of cell outcome on film thickness and dopant choice. The strengths and weaknesses of different synthesis parameters, as demonstrated by these experiments, are critical design factors that must be leveraged when designing biomedical implants. The results of these studies should provide practical insight to researchers working with conducting polymers, and particularly PPy, on the relationships between synthesis parameters, polymeric properties and biological compatibility.
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Affiliation(s)
- John M Fonner
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas, 1 University Station, MC C0800, Austin, TX 78712, USA
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30
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Schaefer AW, Schoonderwoert VTG, Ji L, Mederios N, Danuser G, Forscher P. Coordination of actin filament and microtubule dynamics during neurite outgrowth. Dev Cell 2008; 15:146-62. [PMID: 18606148 DOI: 10.1016/j.devcel.2008.05.003] [Citation(s) in RCA: 180] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2006] [Revised: 01/16/2008] [Accepted: 05/05/2008] [Indexed: 01/07/2023]
Abstract
Although much evidence suggests that axon growth and guidance depend on well-coordinated cytoskeletal dynamics, direct characterization of the corresponding molecular events has remained a challenge. Here, we address this outstanding problem by examining neurite outgrowth stimulated by local application of cell adhesion substrates. During acute outgrowth, the advance of organelles and underlying microtubules was correlated with regions of attenuated retrograde actin network flow in the periphery. Interestingly, as adhesion sites matured, contractile actin arc structures, known to be regulated by the Rho/Rho Kinase/myosin II signaling cascade, became more robust and coordinated microtubule movements in the growth cone neck. When Rho Kinase was inhibited, although growth responses occurred with less of a delay, microtubules failed to consolidate into a single axis of growth. These results reveal a role for Rho Kinase and myosin II contractility in regulation of microtubule behavior during neuronal growth.
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Affiliation(s)
- Andrew W Schaefer
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511, USA
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31
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Cox BC, Marritt AM, Perry DC, Kellar KJ. Transport of multiple nicotinic acetylcholine receptors in the rat optic nerve: high densities of receptors containing alpha6 and beta3 subunits. J Neurochem 2008; 105:1924-38. [PMID: 18266937 DOI: 10.1111/j.1471-4159.2008.05282.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are abundant in the rat retina and at least seven heteromeric subtypes have been detected. Axons of retinal ganglion cells form the optic nerve and innervate areas of the brain important for visual processing, including the lateral geniculate nucleus, the superior colliculus, and the pretectal nucleus. Development of eye-specific layers in these projection areas are dependent upon retinal waves which are initially mediated by nAChRs [Feller et al., Science 272 (1996), 1182; Penn et al., Science 279 (1998), 2108; Bansal et al., J. Neurosci. 20 (2000), 7672]. Unilateral eye-enucleation studies in the rat indicate that nAChRs are on the terminals of optic nerve axons, where they may mediate influences of acetylcholine on visual pathways. In this study, we use radioligand binding and immunoprecipitation with subunit-selective antibodies to investigate the subunit composition of nAChRs in the rat optic nerve. We found multiple nAChR subtypes in the optic nerve, all of which contain the beta2 subunit. Most of these receptors are mixed heteromeric subtypes, composed of at least three different subunits. Included among these subtypes is the highest percentage and density of alpha6- and beta3-containing nAChRs of any area of the rat CNS that has been reported.
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Affiliation(s)
- Brandon C Cox
- Department of Pharmacology, Georgetown University School of Medicine, Washington, Washington DC, USA
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32
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Local stabilization of microtubule assembly improves recovery of facial nerve function after repair. Exp Neurol 2008; 209:131-44. [DOI: 10.1016/j.expneurol.2007.09.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2007] [Revised: 09/03/2007] [Accepted: 09/10/2007] [Indexed: 11/23/2022]
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33
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Tokuo H, Mabuchi K, Ikebe M. The motor activity of myosin-X promotes actin fiber convergence at the cell periphery to initiate filopodia formation. ACTA ACUST UNITED AC 2007; 179:229-38. [PMID: 17954606 PMCID: PMC2064759 DOI: 10.1083/jcb.200703178] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Filopodia are actin-rich fingerlike protrusions found at the leading edge of migrating cells and are believed to play a role in directional sensing. Previous studies have shown that myosin-X (myoX) promotes filopodia formation and that this is mediated through its ability to deliver specific cargoes to the cell periphery (Tokuo, H., and M. Ikebe. 2004. Biochem Biophys. Commun. 319:214-220; Zhang, H., J.S. Berg, Z. Li, Y. Wang, P. Lang, A.D. Sousa, A. Bhaskar, R.E. Cheney, and S. Stromblad. 2004. Nat. Cell Biol. 6:523-531; Bohil, A.B., B.W. Robertson, and R.E. Cheney. 2006. Proc. Natl. Acad. Sci. USA. 103:12411-12416; Zhu, X.J., C.Z. Wang, P.G. Dai, Y. Xie, N.N. Song, Y. Liu, Q.S. Du, L. Mei, Y.Q. Ding, and W.C. Xiong. 2007. Nat. Cell Biol. 9:184-192). In this study, we show that the motor function of myoX and not the cargo function is critical for initiating filopodia formation. Using a dimer-inducing technique, we find that myoX lacking its cargo-binding tail moves laterally at the leading edge of lamellipodia and induces filopodia in living cells. We conclude that the motor function of the two-headed form of myoX is critical for actin reorganization at the leading edge, leading to filopodia formation.
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Affiliation(s)
- Hiroshi Tokuo
- Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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Dwivedy A, Gertler FB, Miller J, Holt CE, Lebrand C. Ena/VASP function in retinal axons is required for terminal arborization but not pathway navigation. Development 2007; 134:2137-46. [PMID: 17507414 PMCID: PMC3792372 DOI: 10.1242/dev.002345] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family of proteins is required for filopodia formation in growth cones and plays a crucial role in guidance cue-induced remodeling of the actin cytoskeleton. In vivo studies with pharmacological inhibitors of actin polymerization have previously provided evidence for the view that filopodia are needed for growth cone navigation in the developing visual pathway. Here we have re-examined this issue using an alternative strategy to generate growth cones without filopodia in vivo by artificially targeting Xena/XVASP (Xenopus homologs of Ena/VASP) proteins to mitochondria in retinal ganglion cells (RGCs). We used the specific binding of the EVH1 domain of the Ena/VASP family of proteins with the ligand motif FP4 to sequester the protein at the mitochondria surface. RGCs with reduced function of Xena/XVASP proteins extended fewer axons out of the eye and possessed dynamic lamellipodial growth cones missing filopodia that advanced slowly in the optic tract. Surprisingly, despite lacking filopodia, the axons navigated along the optic pathway without obvious guidance errors, indicating that the Xena/XVASP family of proteins and filopodial protrusions are non-essential for pathfinding in retinal axons. However, depletion of Xena/XVASP proteins severely impaired the ability of growth cones to form branches within the optic tectum, suggesting that this protein family, and probably filopodia, plays a key role in establishing terminal arborizations.
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Affiliation(s)
- Asha Dwivedy
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
| | - Frank B. Gertler
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jeffrey Miller
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Christine E. Holt
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
| | - Cecile Lebrand
- Département de Biologie Cellulaire et de Morphologie, University of Lausanne, Rue de Bugnon, 9, 1005 Lausanne, Switzerland
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Madura T, Kubo T, Tanag M, Matsuda K, Tomita K, Yano K, Hosokawa K. The Rho-Associated Kinase Inhibitor Fasudil Hydrochloride Enhances Neural Regeneration after Axotomy in the Peripheral Nervous System. Plast Reconstr Surg 2007; 119:526-35. [PMID: 17230085 DOI: 10.1097/01.prs.0000246380.40596.29] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND The Rho family of small GTPases is responsible for various processes involving actin cytoskeleton in eukaryotic cells, including neurite outgrowth. Several substances found at the peripheral nerve injury site were shown to activate one member of this family, Rho. The activation of Rho leads to neurite outgrowth inhibition and the development of posttraumatic neuropathic pain. The authors used the clinically tested Rho-associated kinase inhibitor fasudil hydrochloride to enhance the functional recovery of the peripheral nerve in the rat. METHODS In the peroneal nerve interpositional graft model, the authors administered fasudil (experimental groups) or saline (control groups) (1) intraperitoneally and (2) directly into the graft by microinjection (n = 6 animals per experimental condition). Neural recovery was assessed during postoperative follow-up lasting 80 days by peroneal functional index, electrophysiologic, and histomorphometric analyses. RESULTS The peroneal functional index returned to values not significantly different from preoperative values on days 55 (fasudil injected into the graft) and 60 (fasudil injected intraperitoneally) in the experimental groups. In the control groups, this took 70 (saline injected intraperitoneally) and 75 days (saline injected into the graft). These results are supported by electrophysiologic and histomorphologic assessments. CONCLUSIONS The authors determined that fasudil hydrochloride was capable of accelerating the functional regeneration after peripheral nerve axotomy, which is consistent with the results of reports about Rho cascade disruption in the central nervous system. Because fasudil hydrochloride is a clinically tested drug, it could be used to enhance neural regeneration in human patients as well.
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Affiliation(s)
- Tomas Madura
- Department of Plastic Surgery, Osaka University Graduate School of Medicine, Osaka, Japan.
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Zhang CL, Wilson JA, Williams J, Chiu SY. Action Potentials Induce Uniform Calcium Influx in Mammalian Myelinated Optic Nerves. J Neurophysiol 2006; 96:695-709. [PMID: 16835363 DOI: 10.1152/jn.00083.2006] [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: 11/22/2022] Open
Abstract
The myelin sheath enables saltatory conduction by demarcating the axon into a narrow nodal region for excitation and an extended, insulated internodal region for efficient spread of passive current. This anatomical demarcation produces a dramatic heterogeneity in ionic fluxes during excitation, a classical example being the restriction of Na influx at the node. Recent studies have revealed that action potentials also induce calcium influx into myelinated axons of mammalian optic nerves. Does calcium influx in myelinated axons show spatial heterogeneity during nerve excitation? To address this, we analyzed spatial profiles of axonal calcium transients during action potentials by selectively staining axons with calcium indicators and subjected the data to theoretical analysis with parameters for axial calcium diffusion empirically determined using photolysis of caged compounds. The results show surprisingly that during action potentials, calcium influx occurs uniformly along an axon of a fully myelinated mouse optic nerve.
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Affiliation(s)
- Chuan-Li Zhang
- Dept. of Physiology, University of Wisconsin School of Medicine, 1300 University Ave., 277 Medical Science Bldg., Madison, WI 53706, USA
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Shekarabi M, Moore SW, Tritsch NX, Morris SJ, Bouchard JF, Kennedy TE. Deleted in colorectal cancer binding netrin-1 mediates cell substrate adhesion and recruits Cdc42, Rac1, Pak1, and N-WASP into an intracellular signaling complex that promotes growth cone expansion. J Neurosci 2006; 25:3132-41. [PMID: 15788770 PMCID: PMC6725078 DOI: 10.1523/jneurosci.1920-04.2005] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Extracellular cues direct axon extension by regulating growth cone morphology. The netrin-1 receptor deleted in colorectal cancer (DCC) is required for commissural axon extension to the floor plate in the embryonic spinal cord. Here we demonstrate that challenging embryonic rat spinal commissural neurons with netrin-1, either in solution or as a substrate, causes DCC-dependent increases in growth cone surface area and filopodia number, which we term growth cone expansion. We provide evidence that DCC influences growth cone morphology by at least two mechanisms. First, DCC mediates an adhesive interaction with substrate-bound netrin-1. Second, netrin-1 binding to DCC recruits an intracellular signaling complex that directs the organization of actin. We show that netrin-1-induced growth cone expansion requires Cdc42 (cell division cycle 42), Rac1 (Ras-related C3 botulinum toxin substrate 1), Pak1 (p21-activated kinase), and N-WASP (neuronal Wiskott-Aldrich syndrome protein) and that the application of netrin-1 rapidly activates Cdc42, Rac1, and Pak1. Furthermore, netrin-1 recruits Cdc42, Rac1, Pak1, and N-WASP into a complex with the intracellular domain of DCC and Nck1. These findings suggest that DCC influences growth cone morphology by acting both as a transmembrane bridge that links extracellular netrin-1 to the actin cytoskeleton and as the core of a protein complex that directs the organization of actin.
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Affiliation(s)
- Masoud Shekarabi
- Center for Neuronal Survival, Montréal Neurological Institute, McGill University, Montréal, Québec, Canada H3A 2B4
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Pannu R, Barbosa E, Singh AK, Singh I. Attenuation of acute inflammatory response by atorvastatin after spinal cord injury in rats. J Neurosci Res 2005; 79:340-50. [PMID: 15605375 DOI: 10.1002/jnr.20345] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Spinal cord injury (SCI) is a devastating and complex clinical condition involving proinflammatory cytokines and nitric oxide toxicity that produces a predictable pattern of progressive injury entailing neuronal loss, axonal destruction, and demyelination at the site of impact. The involvement of proinflammatory cytokines and inducible nitric oxide synthase (iNOS) in exacerbation of SCI pathology is well documented. We have reported previously the antiinflammatory properties and immunomodulatory activities of statins (3-hydroxy-3-methylglutaryl [HMG]-CoA reductase inhibitors) in the animal model of multiple sclerosis, experimental allergic encephalitis (EAE). The present study was undertaken to investigate the efficacy of atorvastatin (Lipitor; LP) treatment in attenuating SCI-induced pathology. Immunohistochemical detection and real-time PCR analysis showed increased expression of iNOS, tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL-1beta) after SCI. In addition, neuronal apoptosis was detected 24 hr after injury followed by a profound increase in ED1-positive inflammatory infiltrates, glial fibrillary acidic protein (GFAP)-positive reactive astrocytes, and oligodendrocyte apoptosis by 1 week after SCI relative to control. LP treatment attenuated the SCI-induced iNOS, TNFalpha, and IL-1beta expression. LP also provided protection against SCI-induced tissue necrosis, neuronal and oligodendrocyte apoptosis, demyelination, and reactive gliosis. Furthermore, rats treated with LP scored much higher on the locomotor rating scale after SCI (19.13 +/- 0.53) than did untreated rats (9.04 +/- 1.22). This study therefore reports the beneficial effect of atorvastatin for the treatment of SCI-related pathology and disability.
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Affiliation(s)
- Ravinder Pannu
- Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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Williams R, Ryves WJ, Dalton EC, Eickholt B, Shaltiel G, Agam G, Harwood AJ. A molecular cell biology of lithium. Biochem Soc Trans 2005; 32:799-802. [PMID: 15494019 DOI: 10.1042/bst0320799] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Lithium (Li(+)), a mood stabilizer, has profound effects on cultured neurons, offering an opportunity to investigate its cellular biological effects. Here we consider the effect of Li(+) and other psychotropic drugs on growth cone morphology and chemotaxis. Li(+) inhibits GSK-3 (glycogen synthase kinase-3) at a therapeutically relevant concentration. Treated cells show a number of features that arise due to GSK-3 inhibition, such as altered microtubule dynamics, axonal branching and loss of semaphorin 3A-mediated growth cone collapse. Li(+) also causes growth cones to spread; however, a similar effect is seen with two other mood stabilizers, valproic acid and carbamazepine, but without changes in microtubules or axon branching. This common effect of mood stabilizers is mediated by changes in inositol phosphate signalling, not GSK-3 activity. Given the presence of neurogenesis in the adult brain, we speculate that changes in growth cone behaviour could also occur during treatment of mental disorders.
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Affiliation(s)
- R Williams
- MRC Laboratory for Molecular Cell Biology and Department of Biology, University College London, Gower St, London WC1E 6BT, UK
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Breugem CC, Hennekam RCM, van Gemert MJC, van der Horst CMAM. Are Capillary Malformations Neurovenular or Purely Neural? Plast Reconstr Surg 2005; 115:578-87. [PMID: 15692368 DOI: 10.1097/01.prs.0000150150.69479.70] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Corstiaan C Breugem
- Department of Plastic, Reconstructive, and Hand Surgery, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
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Sahly I, Khoutorsky A, Erez H, Prager-Khoutorsky M, Spira ME. On-line confocal imaging of the events leading to structural dedifferentiation of an axonal segment into a growth cone after axotomy. J Comp Neurol 2005; 494:705-20. [PMID: 16374810 DOI: 10.1002/cne.20690] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The transformation of a transected axonal tip into a growth cone (GC) after axotomy is a critical step in the cascade of events leading to regeneration. However, the mechanisms underlying it are largely unknown. In earlier studies we reported that axotomy of cultured Aplysia neurons leads to a transient and local increase in the free intracellular Ca2+ concentration, calpain activation, and localized proteolysis of the submembranal spectrin. In a recent ultrastructural study, we reported that calpain activation is critical for the restructuring of the microtubules and neurofilaments at the cut axonal end to form a compartment in which vesicles accumulate. By using on-line confocal imaging of microtubules (MTs), actin, and vesicles in cultured Aplysia neurons, we studied the kinetics of the transformation and examined some of the mechanisms that orchestrate it. We report that perturbation of the MTs' polymerization by nocodazole inhibits the formation of an MT-based compartment in which the vesicles accumulate, yet actin repolymerization proceeds normally to form a nascent GC's lamellipodium. Nevertheless, under these conditions, the lamellipodium fails to expand and form neurites. When actin filament polymerization is inhibited by cytochalasin D or jasplakinolide, the MT-based compartment is formed and vesicles accumulate at the cut axonal end. However, a GC's lamellipodium is not formed, and the cut axonal end fails to regenerate. A growth-competent GC is formed only when MT restructuring, the accumulation of vesicles, and actin polymerization properly converge in time and space.
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Affiliation(s)
- Iman Sahly
- Department of Neurobiology, Institute of Life Science, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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Abstract
The human brain assembles an incredible network of over a billion neurons. Understanding how these connections form during development in order for the brain to function properly is a fundamental question in biology. Much of this wiring takes place during embryonic development. Neurons are generated in the ventricular zone, migrate out, and begin to differentiate. However, neurons are often born in locations some distance from the target cells with which they will ultimately form connections. To form connections, neurons project long axons tipped with a specialized sensing device called a growth cone. The growing axons interact directly with molecules within the environment through which they grow. In order to find their targets, axonal growth cones use guidance molecules that can either attract or repel them. Understanding what these guidance cues are, where they are expressed, and how the growth cone is able to transduce their signal in a directionally specific manner is essential to understanding how the functional brain is constructed. In this chapter, we review what is known about the mechanisms involved in axonal guidance. We discuss how the growth cone is able to sense and respond to its environment and how it is guided by pioneering cells and axons. As examples, we discuss current models for the development of the spinal cord, the cerebral cortex, and the visual and olfactory systems.
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Affiliation(s)
- Céline Plachez
- Department of Anatomy and Neurobiology, University of Maryland, School of Medicine, Baltimore, Maryland 21201, USA
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Dash PK, Orsi SA, Moody M, Moore AN. A role for hippocampal Rho–ROCK pathway in long-term spatial memory. Biochem Biophys Res Commun 2004; 322:893-8. [PMID: 15336547 DOI: 10.1016/j.bbrc.2004.08.004] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2004] [Indexed: 11/17/2022]
Abstract
Morphological changes, including changes in size, shape, and number of synapses, in neurons have been observed in many species and are thought to be critical for long-term memory storage. Actin filaments are intimately involved in neuronal morphology and regulation of their dynamics can influence memory. Rho GTPase plays a prominent role in this process and has been implicated in both pre- and post-synaptic morphological changes. Therefore, we examined the effect of hippocampal manipulation of Rho and ROCK activity on performance in a spatial memory task. Post-training intrahippocampal infusion of an inhibitor of the downstream effector kinase p160ROCK impaired long-term memory. Furthermore, post-training activation of Rho using lysophosphatidic acid (LPA) enhanced long-term spatial memory. This memory enhancing effect of LPA was not mediated via the Erk cascade, as no change in Erk phosphorylation was observed as a result of its administration. Our results demonstrate a role for the Rho-ROCK pathway in hippocampus-dependent spatial memory.
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Affiliation(s)
- Pramod K Dash
- Department of Neurobiology and Anatomy, The Vivian L. Smith Center for Neurologic Research, The University of Texas Medical School, Houston, TX, USA.
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Abstract
It has been recognized for a long time that the neuronal cytoskeleton plays an important part in neurite growth and growth cone pathfinding, the mechanism by which growing axons find an appropriate route through the developing embryo to their target cells. In the growth cone, many intracellular signaling pathways that are activated by guidance cues converge on the growth cone cytoskeleton and regulate its dynamics. Most of the research effort in this area has focussed on the actin, microfilament cytoskeleton of the growth cone, principally because it underlies growth cone motility, the extension and retraction of filopodia and lamellipodia, and these structures are the first to encounter guidance cues during growth cone advance. However, more recently, it has become apparent that the microtubule cytoskeleton also has a role in growth cone pathfinding and is also regulated by guidance cues operating through intracellular signaling pathways via engagement with cell membrane receptors. Furthermore, recent work has revealed an interaction between these two components of the growth cone cytoskeleton that is probably essential for growth cone turning, a fundamental growth cone behavior during pathfinding. In this short review I discuss recent experiments that uncover the function of microtubules in growth cones, how their behavior is regulated, and how they interact with the actin filaments.
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Affiliation(s)
- Phillip R Gordon-Weeks
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, England.
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Abstract
The motile behaviors of growth cones at the ends of elongating axons determine pathways of axonal connections in developing nervous systems. Growth cones express receptors for molecular guidance cues in the local environment, and receptor-guidance cue binding initiates cytoplasmic signaling that regulates the cytoskeleton to control growth cone advance, turning, and branching behaviors. The dynamic actin filaments of growth cones are frequently targets of this regulatory signaling. Rho GTPases are key mediators of signaling by guidance cues, although much remains to be learned about how growth cone responses are orchestrated by Rho GTPase signaling to change the dynamics of polymerization, transport, and disassembly of actin filaments. Binding of neurotrophins to Trk and p75 receptors on growth cones triggers changes in actin filament dynamics to regulate several aspects of growth cone behaviors. Activation of Trk receptors mediates local accumulation of actin filaments, while neurotrophin binding to p75 triggers local decrease in RhoA signaling that promotes lengthening of filopodia. Semaphorin IIIA and ephrin-A2 are guidance cues that trigger avoidance or repulsion of certain growth cones, and in vitro responses to these proteins include growth cone collapse. Dynamic changes in the activities of Rho GTPases appear to mediate responses to these cues, although it remains unclear what the changes are in actin filament distribution and dynamic reorganization that result in growth cone collapse. Growth cones in vivo simultaneously encounter positive and negative guidance cues, and thus, growth cone behaviors during axonal pathfinding reflect the complex integration of multiple signaling activities.
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Affiliation(s)
- Gianluca Gallo
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA
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Zhang CL, Verbny Y, Malek SA, Stys PK, Chiu SY. Nicotinic Acetylcholine Receptors in Mouse and Rat Optic Nerves. J Neurophysiol 2004; 91:1025-35. [PMID: 14762152 DOI: 10.1152/jn.00769.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Receptor-mediated calcium signaling in axons of mouse and rat optic nerves was examined by selectively staining the axonal population with a calcium indicator. Nicotine (1-50 μM) induced an axonal calcium elevation that was eliminated when calcium was removed from the bath, suggesting that nicotine induces calcium influx into axons. The nicotine response was blocked by d-tubocurarine and mecamylamine but not α-bungarotoxin, indicating the presence of calcium permeable, non-α7 nicotinic acetylcholine receptor (nAChR) subtype. Agonist efficacy order for eliciting the axonal nAChR calcium response was cytisine ∼ nicotine >> acetylcholine. The nicotine-mediated calcium response was attenuated during the process of normal myelination, decreasing by approximately 10-fold from P1 (premyelinated) to P30 (myelinated). Nicotine also caused a rapid reduction in the compound action potential in neonatal optic nerves, consistent with a shunting of the membrane after opening of the nonspecific cationic nicotinic channels. Voltagegated calcium channels contributed little to the axonal calcium elevation during nAChR activation. During repetitive stimulations, the compound action potential in neonatal mouse optic nerves underwent a gradual reduction in amplitude that could be partially prevented by d-tubocurarine, suggesting an activity-dependent release of acetylcholine that activates axonal AChRs. We conclude that mammalian optic nerve axons express nAChRs and suggest that these receptors are activated in an activity-dependent fashion during optic nerve development to modulate axon excitability and biology.
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Affiliation(s)
- Chuan-Li Zhang
- Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA
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Dent EW, Tang F, Kalil K. Axon guidance by growth cones and branches: common cytoskeletal and signaling mechanisms. Neuroscientist 2003; 9:343-53. [PMID: 14580119 DOI: 10.1177/1073858403252683] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Growing axons are guided to appropriate targets by responses of their motile growth cones to environmental cues. Interstitial axon branching is also an important form of axon guidance in the mammalian CNS. Visualization of growing axons in cortical slices and in dissociated cortical cultures showed that growth cone pausing behaviors demarcate sites of future axon branching. Studies of vertebrate and invertebrate growth cones suggest common mechanisms that regulate growth cone behaviors and axon branching. These include reorganization of the actin and microtubule cytoskeleton, dynamic interactions between microtubules and actin filaments, effects of axon guidance molecules, actions of actin regulatory proteins, and dynamic changes in intracellular calcium signaling. Future challenges will be to extend high-resolution imaging of single neurons to studies of intracellular events in the intact nervous system and to apply knowledge of developmental mechanisms to the promotion of axon sprouting after injury in the adult CNS.
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Affiliation(s)
- Erik W Dent
- Department of Anatomy, University of Wisconsin, Madison 53706, USA
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Abstract
Recent studies indicate the actin and microtubule cytoskeletons are a final common target of many signaling cascades that influence the developing neuron. Regulation of polymer dynamics and transport are crucial for the proper growth cone motility. This review addresses how actin filaments, microtubules, and their associated proteins play crucial roles in growth cone motility, axon outgrowth, and guidance. We present a working model for cytoskeletal regulation of directed axon outgrowth. An important goal for the future will be to understand the coordinated response of the cytoskeleton to signaling cascades induced by guidance receptor activation.
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Affiliation(s)
- Erik W Dent
- Biology Department, 68-270, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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50
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Abstract
Axon growth inhibitors associated with myelin and the glial scar contribute to the failure of axon regeneration in the injured adult mammalian central nervous system (CNS). A number of these inhibitors, their receptors, and signaling pathways have been identified. These inhibitors can now be neutralized by a variety of approaches that point to the possibility of developing new therapeutic strategies to stimulate regeneration after spinal cord injury.
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Affiliation(s)
- Samuel David
- Centre for Research in Neuroscience, McGill University Health Centre, Montreal General Hospital Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada, H3G 1A4.
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