1
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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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Dumoulin A, Stoeckli ET. Looking for Guidance - Models and Methods to Study Axonal Navigation. Neuroscience 2023; 508:30-39. [PMID: 35940454 DOI: 10.1016/j.neuroscience.2022.08.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 07/29/2022] [Accepted: 08/01/2022] [Indexed: 01/17/2023]
Abstract
The molecular mechanisms of neural circuit formation have been of interest to Santiago Ramón y Cajal and thousands of neuroscientists sharing his passion for neural circuits ever since. Cajal was a brilliant observer and taught us about the connections and the morphology of neurons in the adult and developing nervous system. Clearly, we will not learn about molecular mechanisms by just looking at brain sections or cells in culture. Technically, we had to come a long way to today's possibilities that allow us to perturb target gene expression and watch the consequences of our manipulations on navigating axons in situ. In this review, we summarize landmark steps towards modern live-imaging approaches used to study the molecular basis of axon guidance.
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Affiliation(s)
- Alexandre Dumoulin
- Department of Molecular Life Sciences and Neuroscience Center Zurich, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Esther T Stoeckli
- Department of Molecular Life Sciences and Neuroscience Center Zurich, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
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3
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Atherton J, Stouffer M, Francis F, Moores CA. Visualising the cytoskeletal machinery in neuronal growth cones using cryo-electron tomography. J Cell Sci 2022; 135:274968. [PMID: 35383828 PMCID: PMC9016625 DOI: 10.1242/jcs.259234] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Accepted: 03/02/2022] [Indexed: 12/12/2022] Open
Abstract
Neurons extend axons to form the complex circuitry of the mature brain. This depends on the coordinated response and continuous remodelling of the microtubule and F-actin networks in the axonal growth cone. Growth cone architecture remains poorly understood at nanoscales. We therefore investigated mouse hippocampal neuron growth cones using cryo-electron tomography to directly visualise their three-dimensional subcellular architecture with molecular detail. Our data showed that the hexagonal arrays of actin bundles that form filopodia penetrate and terminate deep within the growth cone interior. We directly observed the modulation of these and other growth cone actin bundles by alteration of individual F-actin helical structures. Microtubules with blunt, slightly flared or gently curved ends predominated in the growth cone, frequently contained lumenal particles and exhibited lattice defects. Investigation of the effect of absence of doublecortin, a neurodevelopmental cytoskeleton regulator, on growth cone cytoskeleton showed no major anomalies in overall growth cone organisation or in F-actin subpopulations. However, our data suggested that microtubules sustained more structural defects, highlighting the importance of microtubule integrity during growth cone migration. Summary: Cryo-electron tomographic reconstruction of neuronal growth cone subdomains reveals distinctive F-actin and microtubule cytoskeleton architectures and modulation at molecular detail.
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Affiliation(s)
- Joseph Atherton
- Randall Centre for Cell and Molecular Biophysics, King's College, London SE1 1YR, UK.,Institute of Structural and Molecular Biology, Birkbeck, University of London, London WC1E 7HX, UK
| | - Melissa Stouffer
- INSERM UMR-S 1270, 17 Rue du Fer à Moulin, 75005 Paris, France.,Sorbonne University UMR-S 1270, 4 Place Jussieu, 75005 Paris, France.,Institut du Fer à Moulin, 17 Rue du Fer à Moulin, 75005 Paris, France.,Institute of Science and Technology Austria, Am campus 1, 3400 Klosterneuberg, Austria
| | - Fiona Francis
- INSERM UMR-S 1270, 17 Rue du Fer à Moulin, 75005 Paris, France.,Sorbonne University UMR-S 1270, 4 Place Jussieu, 75005 Paris, France.,Institut du Fer à Moulin, 17 Rue du Fer à Moulin, 75005 Paris, France
| | - Carolyn A Moores
- Institute of Structural and Molecular Biology, Birkbeck, University of London, London WC1E 7HX, UK
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4
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Sánchez-Huertas C, Herrera E. With the Permission of Microtubules: An Updated Overview on Microtubule Function During Axon Pathfinding. Front Mol Neurosci 2021; 14:759404. [PMID: 34924953 PMCID: PMC8675249 DOI: 10.3389/fnmol.2021.759404] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 11/01/2021] [Indexed: 01/27/2023] Open
Abstract
During the establishment of neural circuitry axons often need to cover long distances to reach remote targets. The stereotyped navigation of these axons defines the connectivity between brain regions and cellular subtypes. This chemotrophic guidance process mostly relies on the spatio-temporal expression patterns of extracellular proteins and the selective expression of their receptors in projection neurons. Axon guidance is stimulated by guidance proteins and implemented by neuronal traction forces at the growth cones, which engage local cytoskeleton regulators and cell adhesion proteins. Different layers of guidance signaling regulation, such as the cleavage and processing of receptors, the expression of co-receptors and a wide variety of intracellular cascades downstream of receptors activation, have been progressively unveiled. Also, in the last decades, the regulation of microtubule (MT) assembly, stability and interactions with the submembranous actin network in the growth cone have emerged as crucial effector mechanisms in axon pathfinding. In this review, we will delve into the intracellular signaling cascades downstream of guidance receptors that converge on the MT cytoskeleton of the growing axon. In particular, we will focus on the microtubule-associated proteins (MAPs) network responsible of MT dynamics in the axon and growth cone. Complementarily, we will discuss new evidences that connect defects in MT scaffold proteins, MAPs or MT-based motors and axon misrouting during brain development.
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Affiliation(s)
- Carlos Sánchez-Huertas
- Instituto de Neurociencias, Consejo Superior de Investigaciones Científicas-Universidad Miguel Hernández (CSIC-UMH), Alicante, Spain
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5
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Sengupta T, Koonce NL, Vázquez-Martínez N, Moyle MW, Duncan LH, Emerson SE, Han X, Shao L, Wu Y, Santella A, Fan L, Bao Z, Mohler W, Shroff H, Colón-Ramos DA. Differential adhesion regulates neurite placement via a retrograde zippering mechanism. eLife 2021; 10:71171. [PMID: 34783657 PMCID: PMC8843091 DOI: 10.7554/elife.71171] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 11/15/2021] [Indexed: 11/13/2022] Open
Abstract
During development, neurites and synapses segregate into specific neighborhoods or layers within nerve bundles. The developmental programs guiding placement of neurites in specific layers, and hence their incorporation into specific circuits, are not well understood. We implement novel imaging methods and quantitative models to document the embryonic development of the C. elegans brain neuropil, and discover that differential adhesion mechanisms control precise placement of single neurites onto specific layers. Differential adhesion is orchestrated via developmentally-regulated expression of the IgCAM SYG-1, and its partner ligand SYG-2. Changes in SYG-1 expression across neuropil layers result in changes in adhesive forces, which sort SYG-2-expressing neurons. Sorting to layers occurs, not via outgrowth from the neurite tip, but via an alternate mechanism of retrograde zippering, involving interactions between neurite shafts. Our study indicates that biophysical principles from differential adhesion govern neurite placement and synaptic specificity in vivo in developing neuropil bundles.
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Affiliation(s)
- Titas Sengupta
- Yale University School of Medicine, New Haven, United States
| | - Noelle L Koonce
- Yale University School of Medicine, New Haven, United States
| | | | - Mark W Moyle
- Yale University School of Medicine, New Haven, United States
| | | | - Sarah E Emerson
- Yale University School of Medicine, New Haven, United States
| | - Xiaofei Han
- National Institutes of Health, Bethesda, United States
| | - Lin Shao
- Yale University School of Medicine, New Haven, United States
| | - Yicong Wu
- National Institutes of Health, Bethesda, United States
| | - Anthony Santella
- Developmental Biology Program, Molecular Cytology Core, Sloan-Kettering Institute, New York, United States
| | - Li Fan
- Helen and Robert Appel Alzheimer's Disease Institute, Weill Cornell Medicine, New York, United States
| | - Zhirong Bao
- Developmental Biology Program, Sloan-Kettering Institute, New York, United States
| | - William Mohler
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, United States
| | - Hari Shroff
- National Institutes of Health, Bethesda, United States
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6
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Kundu T, Dutta P, Nagar D, Maiti S, Ghose A. Coupling of dynamic microtubules to F-actin by Fmn2 regulates chemotaxis of neuronal growth cones. J Cell Sci 2021; 134:jcs252916. [PMID: 34313311 DOI: 10.1242/jcs.252916] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 05/26/2021] [Indexed: 12/20/2022] Open
Abstract
Dynamic co-regulation of the actin and microtubule subsystems enables the highly precise and adaptive remodelling of the cytoskeleton necessary for critical cellular processes, such as axonal pathfinding. The modes and mediators of this interpolymer crosstalk, however, are inadequately understood. We identify Fmn2, a non-diaphanous-related formin associated with cognitive disabilities, as a novel regulator of cooperative actin-microtubule remodelling in growth cones of both chick and zebrafish neurons. We show that Fmn2 stabilizes microtubules in the growth cones of cultured spinal neurons and in vivo. Super-resolution imaging revealed that Fmn2 facilitates guidance of exploratory microtubules along actin bundles into the chemosensory filopodia. Using live imaging, biochemistry and single-molecule assays, we show that a C-terminal domain in Fmn2 is necessary for the dynamic association between microtubules and actin filaments. In the absence of the cross-bridging function of Fmn2, filopodial capture of microtubules is compromised, resulting in destabilized filopodial protrusions and deficits in growth cone chemotaxis. Our results uncover a critical function for Fmn2 in actin-microtubule crosstalk in neurons and demonstrate that the modulation of microtubule dynamics via associations with F-actin is central to directional motility.
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Affiliation(s)
- Tanushree Kundu
- Indian Institute of Science Education and Research (IISER) Pune, Dr Homi Bhabha Road, Pune 411008, India
| | - Priyanka Dutta
- Indian Institute of Science Education and Research (IISER) Pune, Dr Homi Bhabha Road, Pune 411008, India
| | - Dhriti Nagar
- Indian Institute of Science Education and Research (IISER) Pune, Dr Homi Bhabha Road, Pune 411008, India
| | - Sankar Maiti
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, Nadia, West Bengal, India
| | - Aurnab Ghose
- Indian Institute of Science Education and Research (IISER) Pune, Dr Homi Bhabha Road, Pune 411008, India
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7
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Leong SY, Edzuka T, Goshima G, Yamada M. Kinesin-13 and Kinesin-8 Function during Cell Growth and Division in the Moss Physcomitrella patens. THE PLANT CELL 2020; 32:683-702. [PMID: 31919299 PMCID: PMC7054034 DOI: 10.1105/tpc.19.00521] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 10/25/2019] [Accepted: 01/07/2020] [Indexed: 05/03/2023]
Abstract
Kinesin-13 and Kinesin-8 are well-known microtubule (MT) depolymerases that regulate MT length and chromosome movement in animal mitosis. While much is unknown about plant Kinesin-8, Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) Kinesin-13 have been shown to depolymerize MTs in vitro. However, the mitotic function of both kinesins has yet to be determined in plants. Here, we generated complete null mutants of Kinesin-13 and Kinesin-8 in moss (Physcomitrella patens). Both kinesins were found to be nonessential for viability, but the Kinesin-13 knockout (KO) line had increased mitotic duration and reduced spindle length, whereas the Kinesin-8 KO line did not display obvious mitotic defects. Surprisingly, spindle MT poleward flux, which is mediated by Kinesin-13 in animals, was retained in the absence of Kinesin-13. MT depolymerase activity was not detectable for either kinesin in vitro, while MT catastrophe-inducing activity (Kinesin-13) or MT gliding activity (Kinesin-8) was observed. Interestingly, both KO lines showed waviness in their protonema filaments, which correlated with positional instability of the MT foci in their tip cells. Taken together, the results suggest that plant Kinesin-13 and Kinesin-8 have diverged in both mitotic function and molecular activity, acquiring roles in regulating MT foci positioning for directed tip growth.
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Affiliation(s)
- Shu Yao Leong
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Tomoya Edzuka
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Gohta Goshima
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Moé Yamada
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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8
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Clarke A, McQueen PG, Fang HY, Kannan R, Wang V, McCreedy E, Buckley T, Johannessen E, Wincovitch S, Giniger E. Dynamic morphogenesis of a pioneer axon in Drosophila and its regulation by Abl tyrosine kinase. Mol Biol Cell 2020; 31:452-465. [PMID: 31967935 PMCID: PMC7185889 DOI: 10.1091/mbc.e19-10-0563] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The fundamental problem in axon growth and guidance is to understand how cytoplasmic signaling modulates the cytoskeleton to produce directed growth cone motility. We here dissect this process using live imaging of the TSM1 axon of the developing Drosophila wing. We find that the growth cone is almost purely filopodial, and that it extends by a protrusive mode of growth. Quantitative analysis reveals two separate groups of growth cone properties that together account for growth cone structure and dynamics. The core morphological features of the growth cone are strongly correlated with one another and define two discrete morphs. Genetic manipulation of a critical mediator of axon guidance signaling, Abelson (Abl) tyrosine kinase, shows that while Abl weakly modulates the ratio of the two morphs it does not greatly change their properties. Rather, Abl primarily regulates the second group of properties, which report the organization and distribution of actin in the growth cone and are coupled to growth cone velocity. Other experiments dissect the nature of that regulation of actin organization and how it controls the spatial localization of filopodial dynamics and thus axon extension. Together, these observations suggest a novel, probabilistic mechanism by which Abl biases the stochastic fluctuations of growth cone actin to direct axon growth and guidance.
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Affiliation(s)
- Akanni Clarke
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.,Department of Biochemistry and Molecular Medicine, George Washington University School of Medicine/NIH Graduate Partnership Program, Washington, DC 20037
| | - Philip G McQueen
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Hsiao Yu Fang
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Ramakrishnan Kannan
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Victor Wang
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Evan McCreedy
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Tyler Buckley
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Erika Johannessen
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Stephen Wincovitch
- National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892
| | - Edward Giniger
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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9
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Clarke A, McQueen PG, Fang HY, Kannan R, Wang V, McCreedy E, Wincovitch S, Giniger E. Abl signaling directs growth of a pioneer axon in Drosophila by shaping the intrinsic fluctuations of actin. Mol Biol Cell 2020; 31:466-477. [PMID: 31967946 PMCID: PMC7185895 DOI: 10.1091/mbc.e19-10-0564] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The fundamental problem in axon growth and guidance is understanding how cytoplasmic signaling modulates the cytoskeleton to produce directed growth cone motility. Live imaging of the TSM1 axon of the developing Drosophila wing has shown that the essential role of the core guidance signaling molecule, Abelson (Abl) tyrosine kinase, is to modulate the organization and spatial localization of actin in the advancing growth cone. Here, we dissect in detail the properties of that actin organization and its consequences for growth cone morphogenesis and motility. We show that advance of the actin mass in the distal axon drives the forward motion of the dynamic filopodial domain that defines the growth cone. We further show that Abl regulates both the width of the actin mass and its internal organization, spatially biasing the intrinsic fluctuations of actin to achieve net advance of the actin, and thus of the dynamic filopodial domain of the growth cone, while maintaining the essential coherence of the actin mass itself. These data suggest a model whereby guidance signaling systematically shapes the intrinsic, stochastic fluctuations of actin in the growth cone to produce axon growth and guidance.
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Affiliation(s)
- Akanni Clarke
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.,Department of Biochemistry and Molecular Medicine, George Washington University School of Medicine/National Institutes of Health Graduate Partnerships Program, Washington, DC 20037
| | - Philip G McQueen
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Hsiao Yu Fang
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Ramakrishnan Kannan
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Victor Wang
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Evan McCreedy
- Center for Information Technology, National Institutes of Health, Bethesda, MD 20892
| | - Stephen Wincovitch
- National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892
| | - Edward Giniger
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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10
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Shao Q, Yang T, Huang H, Majumder T, Khot BA, Khouzani MM, Alarmanazi F, Gore YK, Liu G. Disease-associated mutations in human TUBB3 disturb netrin repulsive signaling. PLoS One 2019; 14:e0218811. [PMID: 31226147 PMCID: PMC6588280 DOI: 10.1371/journal.pone.0218811] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 06/10/2019] [Indexed: 11/28/2022] Open
Abstract
Missense mutations in the human TUBB3 gene cause a variety of neurological disorders associated with defects in axon guidance and neuronal migration, but the underlying molecular mechanisms are not well understood. Recent studies have shown that direct coupling of dynamic TUBB3 in microtubules with netrin receptors is required for netrin-1-mediated axon guidance, and the interaction of netrin-1 repulsive receptor UNC5C with TUBB3 is involved in netrin-1 mediated axonal repulsion. Here, we report that TUBB3 mutations perturb netrin-1/UNC5C repulsive signaling in the developing nervous system. Among twelve mutants reported in previous studies, five of them show significantly reduced interaction with UNC5C in comparison to the wild-type TUBB3. TUBB3 mutants R262C and R62Q exhibit decreased subcellular colocalization with UNC5C in the peripheral area of the growth cone of primary mouse neurons. Netrin-1 reduces the colocalization of UNC5C with wild-type TUBB3, but not TUBB3 mutants R262C or R62Q, in the growth cone. Results from the in vitro cosedimentation assay indicate that netrin-1 inhibits cosedimentation of UNC5C with polymerized microtubules in primary mouse neurons expressing the wild-type TUBB3, but not R262C or R62Q. Expression of either R262C or R62Q not only blocks netrin-1-induced growth cone collapse and axonal repulsion of primary EGL cells in vitro, but also results in axon projections defects of chicken dorsal root ganglion neurons in ovo. Our study reveals that human TUBB3 mutations specifically perturb netrin-1/UNC5C-mediated repulsion.
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Affiliation(s)
- Qiangqiang Shao
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Tao Yang
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Huai Huang
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Tanushree Majumder
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Bhakti Ajit Khot
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | | | - Farrah Alarmanazi
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Yasmin K. Gore
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
| | - Guofa Liu
- Department of Biological Sciences, University of Toledo, Toledo, OH, United States of America
- * E-mail:
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11
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Ryu JR, Kim JH, Cho HM, Jo Y, Lee B, Joo S, Chae U, Nam Y, Cho IJ, Sun W. A monitoring system for axonal growth dynamics using micropatterns of permissive and Semaphorin 3F chemorepulsive signals. LAB ON A CHIP 2019; 19:291-305. [PMID: 30539180 DOI: 10.1039/c8lc00845k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Neurons reach their correct targets by directional outgrowth of axons, which is mediated by attractive or repulsive cues. Growing axons occasionally cross a field of repulsive cues and stop at intermediate targets on the journey to their final destination. However, it is not well-understood how individual growth cones make decisions, and pass through repulsive territory to reach their permissive target regions. We developed a microcontact printing culture system that could trap individual axonal tips in a permissive dot area surrounded by the repulsive signal, semaphorin 3F (Sema3F). Axons of rat hippocampal neurons on the Sema3F/PLL dot array extended in the checkboard pattern with a significantly slow growth rate. The detailed analysis of the behaviors of axonal growth cones revealed the saccadic dynamics in the dot array system. The trapped axonal tips in the permissive area underwent growth cone enlargement with remarkably spiky filopodia, promoting their escape from the Sema3F constraints with straight extension of axons. This structured axonal growth on the dot pattern was disrupted by increased inter-dot distance, or perturbing intracellular signaling machineries. These data indicate that axons grow against repulsive signals by jumping over the repulsive cues, depending on contact signals and intracellular milieu. Our study suggests that our dot array culture system can be used as a screening system to easily and efficiently evaluate ECM or small molecule inhibitors interfering growth cone dynamics leading to controlling axonal growth.
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Affiliation(s)
- Jae Ryun Ryu
- Department of Anatomy, Brain Korea 21, Korea University College of Medicine, Anam-Dong, Sungbuk-Gu, Seoul, 136-705, Republic of Korea.
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12
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Huang H, Yang T, Shao Q, Majumder T, Mell K, Liu G. Human TUBB3 Mutations Disrupt Netrin Attractive Signaling. Neuroscience 2018; 374:155-171. [PMID: 29382549 DOI: 10.1016/j.neuroscience.2018.01.046] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Revised: 01/16/2018] [Accepted: 01/21/2018] [Indexed: 02/07/2023]
Abstract
Heterozygous missense mutations in human TUBB3 gene result in a spectrum of brain malformations associated with defects in axon guidance, neuronal migration and differentiation. However, the molecular mechanisms underlying mutation-related axon guidance abnormalities are unclear. Recent studies have shown that netrin-1, a canonical guidance cue, induced the interaction of TUBB3 with the netrin receptor deleted in colorectal cancer (DCC). Furthermore, TUBB3 is required for netrin-1-induced axon outgrowth, branching and pathfinding. Here, we provide evidence that TUBB3 mutations impair netrin/DCC signaling in the developing nervous system. The interaction of DCC with most TUBB3 mutants (eight out of twelve) is significantly reduced compared to the wild-type TUBB3. TUBB3 mutants R262C and A302V exhibit decreased subcellular colocalization with DCC in the growth cones of primary neurons. Netrin-1 increases the interaction of endogenous DCC with wild-type human TUBB3, but not R262C or A302V, in primary neurons. Netrin-1 also increases co-sedimentation of DCC with polymerized microtubules (MTs) in primary neurons expressing the wild-type TUBB3, but not R262C or A302V. Expression of either R262C or A302V not only suppresses netrin-1-induced neurite outgrowth, branching and attraction in vitro, but also causes defects in spinal cord commissural axon (CA) projection and pathfinding in ovo. Our study reveals that missense TUBB3 mutations specifically disrupt netrin/DCC-mediated attractive signaling.
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Affiliation(s)
- Huai Huang
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA
| | - Tao Yang
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA
| | - Qiangqiang Shao
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA
| | - Tanushree Majumder
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA
| | - Kristopher Mell
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA
| | - Guofa Liu
- Department of Biological Sciences, University of Toledo, 2801 West Bancroft St., Toledo, OH 43606, USA.
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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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Kif1B Interacts with KBP to Promote Axon Elongation by Localizing a Microtubule Regulator to Growth Cones. J Neurosci 2017; 36:7014-26. [PMID: 27358458 DOI: 10.1523/jneurosci.0054-16.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 05/19/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Delivery of proteins and organelles to the growth cone during axon extension relies on anterograde transport by kinesin motors. Though critical for neural circuit development, the mechanisms of cargo-specific anterograde transport during axon extension are only starting to be explored. Cargos of particular importance for axon outgrowth are microtubule modifiers, such as SCG10 (Stathmin-2). SCG10 is expressed solely during axon extension, localized to growth cones, and essential for axon outgrowth; however, the mechanisms of SCG10 transport and activity were still debated. Using zebrafish mutants and in vivo imaging, we identified the Kif1B motor and its interactor Kif1 binding protein (KBP) as critical for SCG10 transport to axon growth cones and complete axon extension. Axon truncation in kbp(st23) mutants can be suppressed by SCG10 overexpression, confirming the direct relationship between decreased SCG10 levels and failed axon outgrowth. Live imaging revealed that the reduced levels of SCG10 in kbp(st23) mutant growth cones led to altered microtubule stability, defining the mechanistic basis of axon truncation. Thus, our data reveal a novel role for the Kif1B-KBP complex in the anterograde transport of SCG10, which is necessary for proper microtubule dynamics and subsequent axon extension. SIGNIFICANCE STATEMENT Together, our data define the mechanistic underpinnings of failed axon outgrowth with loss of KBP or its associated motor, Kif1B. In addition, we provide conclusive evidence that this defect results from disruption of anterograde transport of SCG10. This is one of the first examples of a motor to be implicated in the essential transport of a discreet cargo necessary for axon extension. In addition, counter to previous in vitro and cell culture results, neither loss of the Kif1B motor nor KBP resulted in inhibition of mitochondrial transport. Altogether, our work links transport of SCG10 to the regulation of microtubule dynamics in the axon growth cone and enhances our understanding of this process during axon outgrowth.
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Erdogan B, Cammarata GM, Lee EJ, Pratt BC, Francl AF, Rutherford EL, Lowery LA. The microtubule plus-end-tracking protein TACC3 promotes persistent axon outgrowth and mediates responses to axon guidance signals during development. Neural Dev 2017; 12:3. [PMID: 28202041 PMCID: PMC5312526 DOI: 10.1186/s13064-017-0080-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Accepted: 02/06/2017] [Indexed: 12/14/2022] Open
Abstract
Background Formation of precise neuronal connections requires proper axon guidance. Microtubules (MTs) of the growth cone provide a critical driving force during navigation of the growing ends of axons. Pioneer MTs and their plus-end tracking proteins (+TIPs) are thought to play integrative roles during this navigation. TACC3 is a + TIP that we have previously implicated in regulating MT dynamics within axons. However, the role of TACC3 in axon guidance has not been previously explored. Results Here, we show that TACC3 is required to promote persistent axon outgrowth and prevent spontaneous axon retractions in embryonic Xenopus laevis neurons. We also show that overexpressing TACC3 can counteract the depolymerizing effect of low doses of nocodazole, and that TACC3 interacts with MT polymerase XMAP215 to promote axon outgrowth. Moreover, we demonstrate that manipulation of TACC3 levels interferes with the growth cone response to the axon guidance cue Slit2 ex vivo, and that ablation of TACC3 causes pathfinding defects in axons of developing spinal neurons in vivo. Conclusion Together, our results suggest that by mediating MT dynamics, the + TIP TACC3 is involved in axon outgrowth and pathfinding decisions of neurons during embryonic development.
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Affiliation(s)
- Burcu Erdogan
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
| | | | - Eric J Lee
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
| | - Benjamin C Pratt
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
| | - Andrew F Francl
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
| | - Erin L Rutherford
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
| | - Laura Anne Lowery
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA.
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Xu Y, Quinn CC. SYD-1 Promotes Multiple Developmental Steps Leading to Neuronal Connectivity. Mol Neurobiol 2016; 53:6768-6773. [PMID: 26660112 PMCID: PMC5841450 DOI: 10.1007/s12035-015-9592-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Accepted: 12/01/2015] [Indexed: 11/30/2022]
Abstract
The establishment of neuronal connectivity requires precise orchestration of multiple developmental steps, including axon specification, axon guidance, selection of synaptic target sites, and development of synaptic specializations. Although these are separate developmental steps, evidence indicates that some of the signaling molecules that regulate these steps are shared. In this review, we focus on SYD-1, a RhoGAP-like protein that has been implicated in each step of axonal development. We discuss interactions between SYD-1, UNC-40(DCC) and RhoGTPases and highlight both similarities and differences in how SYD-1 functions to regulate the different steps of axonal development. These observations reveal an example of how a signaling protein can be repurposed across sequential developmental steps.
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Affiliation(s)
- Yan Xu
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, USA
| | - Christopher C Quinn
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, USA.
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17
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The effect of the NMDA receptor-dependent signaling pathway on cell morphology and melanosome transfer in melanocytes. J Dermatol Sci 2016; 84:296-304. [PMID: 27596138 DOI: 10.1016/j.jdermsci.2016.08.534] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Revised: 06/03/2016] [Accepted: 08/24/2016] [Indexed: 12/26/2022]
Abstract
BACKGROUND The pigmentation of skin and hair in mammals is driven by the intercellular transfer of melanosome from the melanocyte to surrounding keratinocytes However, the detailed molecular mechanism is still a subject of investigation. OBJECTIVE To investigate the effects of N-methyl-d-aspartate (NMDA) receptor-dependent signaling pathway on melanocyte morphologic change and melanosome transfer between melanocytes and keratinocytes. METHODS The expression and the intracellular distribution of NMDA receptor in human melanocyte were analyzed by Western blot and immunofluorescence staining. Melanocytes were treated with 100μM NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine maleate] and 100μM NMDA receptor agonist NMDA, after which the morphological change of melanocyte dendrites and filopodias were observed by scanning electron microscope. The β-tubulin distribution and intracellular calcium concentration ([Ca2+]i) were observed by immunofluorescence staining and flow cytometry under the same treatment respectively. In addition, melanocytes and keratinocytes were co-cultured with or without treatment of MK-801, and the melanosome transfer efficacy were analyzed by flow cytometry. RESULTS We show that human epidermal melanocytes expresses NMDA receptor 1, one subtype of the ionotropic glutamate receptors (iGluRs). Stimulation with agonist of NMDA receptor increased the number of melanocyte filopodia. In contrast, blockage of NMDA receptor with antagonist decreased the number of melanocyte filopodia and this morphological change was accompanied by the disorganization of β-tubulin microfilaments in the intracellular cytoskeleton. In melanocyte-keratinocyte co-cultures, numerous melanocyte filopodia connect to keratinocyte plasma membranes; agonist of NMDA receptor exhibited an increased number of melanocyte filopodia attachments to keratinocyte, while antagonist of NMDA receptor led to a decreased. Moreover, antagonist of NMDA receptor decreased the intracellular calcium concentration in melanocytes and reduced the efficacy of melanosome transfer. CONCLUSION Our data suggest that filopodia delivery is the major mode of melanosome transfer between melanocytes and keratinocytes. NMDA drives melanosome transfer by promoting filopodia delivery and direct morphological effects on melanocytes, while MK-801 affects the intracellular β-tubulin redistribution and the filopodia delivery between melanocytes and keratinocytes. We hypothesize that NMDA receptor-dependent signaling is involved in melanosome transfer, which is associated with calcium influx, cytoskeleton protein redistribution, dendrites and filopodia formation. A thorough understanding of melanosome transfer is crucial for designing treatments for hyper- and hypo-pigmentary disorders of the skin.
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Avila J, Pallas N, Bolós M, Sayas CL, Hernandez F. Intracellular and extracellular microtubule associated protein tau as a therapeutic target in Alzheimer disease and other tauopathies. Expert Opin Ther Targets 2016; 20:653-61. [PMID: 26652296 DOI: 10.1517/14728222.2016.1131269] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
INTRODUCTION Microtubule associated protein tau, a protein mainly expressed in neurons, plays an important role in several diseases related to dementia, named tauopathies. Alzheimer disease is the most relevant tauopathy. The role of tau protein in dementia is now a topic under discussion, and is the focus of this review. AREAS COVERED We have covered two major areas: tau pathology and tau as a therapeutic target. Tau pathology is mainly related to a gain of toxic function due to an abnormal accumulation, aberrant modifications (such as hyperphosphorylation and truncation, among others) and self-aggregation of tau into oligomers or larger structures. Also, tau can be found extracellularly in a toxic form. Tau-based therapy is mainly centered on avoiding the gain of these toxic functions of tau. EXPERT OPINION Tau therapies are focused on lowering tau levels, mainly of modified tau species that could be toxic for neurons (phosphorylated, truncated or aggregated tau), in intracellular or extracellular form. Decreasing the levels of those toxic species is a possible therapeutic strategy.
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Affiliation(s)
- Jesús Avila
- a Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED) , Madrid , Spain.,b Centro de Biología Molecular 'Severo Ochoa' CSIC-UAM , Madrid , Spain
| | - Noemí Pallas
- a Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED) , Madrid , Spain.,b Centro de Biología Molecular 'Severo Ochoa' CSIC-UAM , Madrid , Spain
| | - Marta Bolós
- a Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED) , Madrid , Spain.,b Centro de Biología Molecular 'Severo Ochoa' CSIC-UAM , Madrid , Spain
| | - C Laura Sayas
- c Centre for Biomedical Research of the Canary Islands (CIBICAN), Institute for Biomedical Technologies (ITB) , University of La Laguna (ULL) , Tenerife , Spain
| | - Felix Hernandez
- a Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED) , Madrid , Spain.,b Centro de Biología Molecular 'Severo Ochoa' CSIC-UAM , Madrid , Spain
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19
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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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20
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Menon S, Gupton SL. Building Blocks of Functioning Brain: Cytoskeletal Dynamics in Neuronal Development. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 322:183-245. [PMID: 26940519 PMCID: PMC4809367 DOI: 10.1016/bs.ircmb.2015.10.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neural connectivity requires proper polarization of neurons, guidance to appropriate target locations, and establishment of synaptic connections. From when neurons are born to when they finally reach their synaptic partners, neurons undergo constant rearrangment of the cytoskeleton to achieve appropriate shape and polarity. Of particular importance to neuronal guidance to target locations is the growth cone at the tip of the axon. Growth-cone steering is also dictated by the underlying cytoskeleton. All these changes require spatiotemporal control of the cytoskeletal machinery. This review summarizes the proteins that are involved in modulating the actin and microtubule cytoskeleton during the various stages of neuronal development.
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Affiliation(s)
- Shalini Menon
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, United States of America
| | - Stephanie L Gupton
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, United States of America; Neuroscience Center and Curriculum in Neurobiology, University of North Carolina, Chapel Hill, NC, United States of America; Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, United States of America.
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21
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He Y, Ren Y, Wu B, Decourt B, Lee AC, Taylor A, Suter DM. Src and cortactin promote lamellipodia protrusion and filopodia formation and stability in growth cones. Mol Biol Cell 2015. [PMID: 26224308 PMCID: PMC4569314 DOI: 10.1091/mbc.e15-03-0142] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
How Src tyrosine kinase and cortactin control actin organization and dynamics in neuronal growth cones is not well understood. Using multiple high-resolution imaging techniques, this study shows that Src and cortactin control the persistence of lamellipodial protrusion as well as the formation, stability, and elongation of filopodia in growth cones. Src tyrosine kinases have been implicated in axonal growth and guidance; however, the underlying cellular mechanisms are not well understood. Specifically, it is unclear which aspects of actin organization and dynamics are regulated by Src in neuronal growth cones. Here, we investigated the function of Src2 and one of its substrates, cortactin, in lamellipodia and filopodia of Aplysia growth cones. We found that up-regulation of Src2 activation state or cortactin increased lamellipodial length, protrusion time, and actin network density, whereas down-regulation had opposite effects. Furthermore, Src2 or cortactin up-regulation increased filopodial density, length, and protrusion time, whereas down-regulation promoted lateral movements of filopodia. Fluorescent speckle microscopy revealed that rates of actin assembly and retrograde flow were not affected in either case. In summary, our results support a model in which Src and cortactin regulate growth cone motility by increasing actin network density and protrusion persistence of lamellipodia by controlling the state of actin-driven protrusion versus retraction. In addition, both proteins promote the formation and stability of actin bundles in filopodia.
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Affiliation(s)
- Yingpei He
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
| | - Yuan Ren
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
| | - Bingbing Wu
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
| | - Boris Decourt
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
| | - Aih Cheun Lee
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
| | - Aaron Taylor
- Bindley Bioscience Center, Purdue University, West Lafayette, IN 47907
| | - Daniel M Suter
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907 Bindley Bioscience Center, Purdue University, West Lafayette, IN 47907 )
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Bearce EA, Erdogan B, Lowery LA. TIPsy tour guides: how microtubule plus-end tracking proteins (+TIPs) facilitate axon guidance. Front Cell Neurosci 2015; 9:241. [PMID: 26175669 PMCID: PMC4485311 DOI: 10.3389/fncel.2015.00241] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 06/15/2015] [Indexed: 01/01/2023] Open
Abstract
The growth cone is a dynamic cytoskeletal vehicle, which drives the end of a developing axon. It serves to interpret and navigate through the complex landscape and guidance cues of the early nervous system. The growth cone’s distinctive cytoskeletal organization offers a fascinating platform to study how extracellular cues can be translated into mechanical outgrowth and turning behaviors. While many studies of cell motility highlight the importance of actin networks in signaling, adhesion, and propulsion, both seminal and emerging works in the field have highlighted a unique and necessary role for microtubules (MTs) in growth cone navigation. Here, we focus on the role of singular pioneer MTs, which extend into the growth cone periphery and are regulated by a diverse family of microtubule plus-end tracking proteins (+TIPs). These +TIPs accumulate at the dynamic ends of MTs, where they are well-positioned to encounter and respond to key signaling events downstream of guidance receptors, catalyzing immediate changes in microtubule stability and actin cross-talk, that facilitate both axonal outgrowth and turning events.
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Affiliation(s)
| | - Burcu Erdogan
- Department of Biology, Boston College Chestnut Hill, MA, USA
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23
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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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Popovich PG, Tovar CA, Lemeshow S, Yin Q, Jakeman LB. Independent evaluation of the anatomical and behavioral effects of Taxol in rat models of spinal cord injury. Exp Neurol 2014; 261:97-108. [PMID: 24999028 PMCID: PMC4194241 DOI: 10.1016/j.expneurol.2014.06.020] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 06/22/2014] [Accepted: 06/24/2014] [Indexed: 12/31/2022]
Abstract
The goal of the current manuscript was to replicate published data that show intrathecal infusions of Taxol® (paclitaxel), an anti-neoplastic microtubule stabilizing agent, reduce fibrogliotic scarring caused by a dorsal spinal hemisection (DHx) injury and increase functional recovery and growth of serotonergic axons after moderate spinal contusion injury. These experiments were completed as part of an NIH-NINDS contract entitled "Facilities of Research Excellence in Spinal Cord Injury (FORE-SCI) - Replication". Here, data are presented that confirm the anti-scarring effects of Taxol after DHx injury; however, Taxol did not confer neuroprotection or promote serotonergic axon growth nor did it improve functional recovery in a model of moderate spinal contusion injury. Thus, only partial replication was achieved. Possible explanations for disparate results in our studies and published data are discussed.
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Affiliation(s)
- Phillip G Popovich
- Center for Brain and Spinal Cord Repair, USA; Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, OH, USA.
| | - C Amy Tovar
- Center for Brain and Spinal Cord Repair, USA; Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, OH, USA
| | - Stanley Lemeshow
- Division of Biostatistics, The Ohio State University, College of Public Health, Columbus, OH, USA
| | - Qin Yin
- Center for Brain and Spinal Cord Repair, USA; Department of Physiology and Cell Biology, Wexner Medical Center, The Ohio State University, Columbus, OH, USA
| | - Lyn B Jakeman
- Center for Brain and Spinal Cord Repair, USA; Department of Physiology and Cell Biology, Wexner Medical Center, The Ohio State University, Columbus, OH, USA
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25
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Liu G, Dwyer T. Microtubule dynamics in axon guidance. Neurosci Bull 2014; 30:569-83. [PMID: 24968808 DOI: 10.1007/s12264-014-1444-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 04/10/2014] [Indexed: 12/18/2022] Open
Abstract
Precise modulation of the cytoskeleton is involved in a variety of cellular processes including cell division, migration, polarity, and adhesion. In developing post-mitotic neurons, extracellular guidance cues not only trigger signaling cascades that act at a distance to indirectly regulate microtubule distribution, and assembly and disassembly in the growth cone, but also directly modulate microtubule stability and dynamics through coupling of guidance receptors with microtubules to control growth-cone turning. Microtubule-associated proteins including classical microtubule-associated proteins and microtubule plus-end tracking proteins are required for modulating microtubule dynamics to influence growth-cone steering. Multiple key signaling components, such as calcium, small GTPases, glycogen synthase kinase-3β, and c-Jun N-terminal kinase, link upstream signal cascades to microtubule stability and dynamics in the growth cone to control axon outgrowth and projection. Understanding the functions and regulation of microtubule dynamics in the growth cone provides new insights into the molecular mechanisms of axon guidance.
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Affiliation(s)
- Guofa Liu
- Department of Biological Sciences, University of Toledo, Toledo, OH, 43606, USA,
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26
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Steketee MB, Oboudiyat C, Daneman R, Trakhtenberg E, Lamoureux P, Weinstein JE, Heidemann S, Barres BA, Goldberg JL. Regulation of intrinsic axon growth ability at retinal ganglion cell growth cones. Invest Ophthalmol Vis Sci 2014; 55:4369-77. [PMID: 24906860 DOI: 10.1167/iovs.14-13882] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Mammalian central nervous system neurons fail to regenerate after injury or disease, in part due to a progressive loss in intrinsic axon growth ability after birth. Whether lost axon growth ability is due to limited growth resources or to changes in the axonal growth cone is unknown. METHODS Static and time-lapse images of purified retinal ganglion cells (RGCs) were analyzed for axon growth rate and growth cone morphology and dynamics without treatment and after manipulating Kruppel-like transcription factor (KLF) expression or applying mechanical tension. RESULTS Retinal ganglion cells undergo a developmental switch in growth cone dynamics that mirrors the decline in postnatal axon growth rates, with increased filopodial adhesion and decreased lamellar protrusion area in postnatal axonal growth cones. Moreover, expressing growth-suppressive KLF4 or growth-enhancing KLF6 transcription factors elicits similar changes in postnatal growth cones that correlate with axon growth rates. Postnatal RGC axon growth rate is not limited by an inability to achieve axon growth rates similar to embryonic RGCs; indeed, postnatal axons support elongation rates up to 100-fold faster than postnatal axonal growth rates. Rather, the intrinsic capacity for rapid axon growth is due to both growth cone pausing and retraction, as well as to a slightly decreased ability to achieve rapid instantaneous rates of forward progression. Finally, we observed that RGC axon and dendrite growth are regulated independently in vitro. CONCLUSIONS Together, these data support the hypothesis that intrinsic axon growth rate is regulated by an axon-specific growth program that differentially regulates growth cone motility.
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Affiliation(s)
- Michael B Steketee
- Bascom Palmer Eye Institute and Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida, United States Department of Ophthalmology and McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Carly Oboudiyat
- Bascom Palmer Eye Institute and Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida, United States
| | - Richard Daneman
- Department of Neurobiology, Stanford University School of Medicine, Stanford, California, United States
| | - Ephraim Trakhtenberg
- Bascom Palmer Eye Institute and Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida, United States
| | - Philip Lamoureux
- Department of Physiology, Michigan State University, East Lansing, Michigan, United States
| | - Jessica E Weinstein
- Bascom Palmer Eye Institute and Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida, United States
| | - Steve Heidemann
- Department of Physiology, Michigan State University, East Lansing, Michigan, United States
| | - Ben A Barres
- Department of Neurobiology, Stanford University School of Medicine, Stanford, California, United States
| | - Jeffrey L Goldberg
- Bascom Palmer Eye Institute and Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida, United States Department of Ophthalmology, Shiley Eye Center, University of California San Diego, San Diego, California, United States
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Abstract
Development creates a vast array of forms and patterns with elegant economy, using a small vocabulary of pattern-generating proteins such as BMPs, FGFs and Hh in similar ways in many different contexts. Despite much theoretical and experimental work, the signaling mechanisms that disperse these morphogen signaling proteins remain controversial. Here, we review the conceptual background and evidence that establishes a fundamental and essential role for cytonemes as specialized filopodia that transport signaling proteins between signaling cells. This evidence suggests that cytoneme-mediated signaling is a dispersal mechanism that delivers signaling proteins directly at sites of cell-cell contact.
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Affiliation(s)
- Thomas B. Kornberg
- Cardiovascular Research Institute, University of California, San Francisco, CA 94156, USA
| | - Sougata Roy
- Cardiovascular Research Institute, University of California, San Francisco, CA 94156, USA
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Brown AS, Borgmann-Winter K, Hahn CG, Role L, Talmage D, Gur R, Chow J, Prado P, McCloskey T, Bao Y, Bulinski JC, Dwork AJ. Increased stability of microtubules in cultured olfactory neuroepithelial cells from individuals with schizophrenia. Prog Neuropsychopharmacol Biol Psychiatry 2014; 48:252-258. [PMID: 24513021 PMCID: PMC3999307 DOI: 10.1016/j.pnpbp.2013.10.015] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 10/11/2013] [Accepted: 10/17/2013] [Indexed: 01/08/2023]
Abstract
Microtubules (MTs) are essential components of the cytoskeleton that play critical roles in neurodevelopment and adaptive central nervous system functioning. MTs are essential to growth cone advance and ultrastructural events integral to synaptic plasticity; these functions figure significantly into current pathophysiologic conceptualizations of schizophrenia. To date, no study has directly investigated MT dynamics in humans with schizophrenia. We therefore compared the stability of MTs in olfactory neuroepithelial (OE) cells between schizophrenia cases and matched nonpsychiatric comparison subjects. For this purpose, we applied nocodazole (Nz) to cultured OE cells obtained from tissue biopsies from seven living schizophrenia patients and seven matched comparison subjects; all schizophrenia cases were on antipsychotic medications. Nz allows MT depolymerization to be followed but prevents repolymerization, so that in living cells treated for varying time intervals, the MTs that are stable for a given treatment interval remain. Our readout of MT stability was the time at which fewer than 10 MTs per cell could be distinguished by anti-β-tubulin immunofluorescence. The percentage of cells with ≥10 intact MTs at specified intervals following Nz treatment was estimated by systematic uniform random sampling with Visiopharm software. These analyses showed that the mean percentages of OE cells with intact MTs were significantly greater for schizophrenia cases than for the matched comparison subjects at 10, 15, and 30min following Nz treatment indicating increased MT stability in OE cells from schizophrenia patients (p=0.0007 at 10min; p=0.0008 at 15min; p=0.036 at 30min). In conclusion, we have demonstrated increased MT stability in nearly all cultures of OE cells from individuals with schizophrenia, who received several antipsychotic treatments, versus comparison subjects matched for age and sex. While we cannot rule out a possible confounding effect of antipsychotic medications, these findings may reflect analogous neurobiological events in at least a subset of immature neurons or other cell types during gestation, or newly generated cells destined for the olfactory bulb or hippocampus, suggesting a mechanism that underlies findings of postmortem and neuroimaging investigations of schizophrenia. Future studies aimed at replicating these findings, including samples of medication-naïve subjects with schizophrenia, and reconciling the results with other studies, will be necessary. Although the observed abnormalities may suggest one of a number of putative pathophysiologic anomalies in schizophrenia, this work may ultimately have implications for an improved understanding of pathogenic processes related to this disorder.
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Affiliation(s)
- Alan S. Brown
- Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY 10032, USA,Department of Epidemiology, Columbia University Mailman School of Public Health, 722 W 168th Street, New York, NY 10032, USA,For correspondence regarding the manuscript or requests for reprints, please contact Dr. Alan Brown at New York State Psychiatric Institute, 1051 Riverside Drive, Unit 23, New York, NY 10032; phone: 1-212-543-5629;
| | - Karin Borgmann-Winter
- Cellular and Molecular Neuropathology Program, Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, 125 South 31st Street, Philadelphia, PA 19104, USA
| | - Chang-Gyu Hahn
- Cellular and Molecular Neuropathology Program, Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, 125 South 31st Street, Philadelphia, PA 19104, USA
| | - Lorna Role
- Department of Neurobiology and Behavior, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
| | - David Talmage
- Department of Pharmacology, State University of New York at Stony Brook, Basic Science Tower 8-140, Stony Brook, NY11794, USA
| | - Raquel Gur
- Departments of Psychiatry, Neurology, and Radiology, University of Pennsylvania Medical Center, 10th Floor, Gates Building, Philadelphia, PA 19104, USA
| | - Jacky Chow
- Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY 10032, USA
| | - Patric Prado
- Department of Epidemiology, Columbia University Mailman School of Public Health, 722 W 168th Street, New York, NY 10032, USA
| | - Thelma McCloskey
- Cellular and Molecular Neuropathology Program, Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, 125 South 31st Street, Philadelphia, PA 19104, USA
| | - Yuanyuan Bao
- Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY 10032, USA
| | - J. Chloe Bulinski
- Department of Biological Sciences, Columbia University, 1212 Amsterdam Avenue, New York, NY 10027, USA
| | - Andrew J. Dwork
- Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY 10032, USA,Department of Pathology and Cell Biology, Columbia University, 1051 Riverside Drive, New York, NY 10032, USA,Macedonian Academy of Sciences and Arts, Skopje 1000, Macedonia
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29
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Prokop A, Beaven R, Qu Y, Sánchez-Soriano N. Using fly genetics to dissect the cytoskeletal machinery of neurons during axonal growth and maintenance. J Cell Sci 2013; 126:2331-41. [PMID: 23729743 DOI: 10.1242/jcs.126912] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The extension of long slender axons is a key process of neuronal circuit formation, both during brain development and regeneration. For this, growth cones at the tips of axons are guided towards their correct target cells by signals. Growth cone behaviour downstream of these signals is implemented by their actin and microtubule cytoskeleton. In the first part of this Commentary, we discuss the fundamental roles of the cytoskeleton during axon growth. We present the various classes of actin- and microtubule-binding proteins that regulate the cytoskeleton, and highlight the important gaps in our understanding of how these proteins functionally integrate into the complex machinery that implements growth cone behaviour. Deciphering such machinery requires multidisciplinary approaches, including genetics and the use of simple model organisms. In the second part of this Commentary, we discuss how the application of combinatorial genetics in the versatile genetic model organism Drosophila melanogaster has started to contribute to the understanding of actin and microtubule regulation during axon growth. Using the example of dystonin-linked neuron degeneration, we explain how knowledge acquired by studying axonal growth in flies can also deliver new understanding in other aspects of neuron biology, such as axon maintenance in higher animals and humans.
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Affiliation(s)
- Andreas Prokop
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK.
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30
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Marx A, Godinez WJ, Tsimashchuk V, Bankhead P, Rohr K, Engel U. Xenopus cytoplasmic linker-associated protein 1 (XCLASP1) promotes axon elongation and advance of pioneer microtubules. Mol Biol Cell 2013; 24:1544-58. [PMID: 23515224 PMCID: PMC3655815 DOI: 10.1091/mbc.e12-08-0573] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dynamic microtubules (MTs) are required for neuronal guidance, in which axons extend directionally toward their target tissues. We found that depletion of the MT-binding protein Xenopus cytoplasmic linker-associated protein 1 (XCLASP1) or treatment with the MT drug Taxol reduced axon outgrowth in spinal cord neurons. To quantify the dynamic distribution of MTs in axons, we developed an automated algorithm to detect and track MT plus ends that have been fluorescently labeled by end-binding protein 3 (EB3). XCLASP1 depletion reduced MT advance rates in neuronal growth cones, very much like treatment with Taxol, demonstrating a potential link between MT dynamics in the growth cone and axon extension. Automatic tracking of EB3 comets in different compartments revealed that MTs increasingly slowed as they passed from the axon shaft into the growth cone and filopodia. We used speckle microscopy to demonstrate that MTs experience retrograde flow at the leading edge. Microtubule advance in growth cone and filopodia was strongly reduced in XCLASP1-depleted axons as compared with control axons, but actin retrograde flow remained unchanged. Instead, we found that XCLASP1-depleted growth cones lacked lamellipodial actin organization characteristic of protrusion. Lamellipodial architecture depended on XCLASP1 and its capacity to associate with MTs, highlighting the importance of XCLASP1 in actin-microtubule interactions.
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Affiliation(s)
- Astrid Marx
- Exzellenzcluster CellNetworks, University of Heidelberg, 69120 Heidelberg, Germany
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31
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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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32
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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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33
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Caro-Gonzalez HY, Nejsum LN, Siemers KA, Shaler TA, Nelson WJ, Barth AIM. Mitogen-activated protein kinase (MAPK/ERK) regulates adenomatous polyposis coli during growth-factor-induced cell extension. J Cell Sci 2012; 125:1247-58. [PMID: 22399805 DOI: 10.1242/jcs.095166] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Regulation of the microtubule- and actin-binding protein adenomatous polyposis coli (APC) is crucial for the formation of cell extensions in many cell types. This process requires inhibition of glycogen synthase kinase-3β (GSK-3β), which otherwise phosphorylates APC and decreases APC-mediated microtubule bundling. Although it is assumed, therefore, that APC phosphorylation is decreased during initiation of cell extensions, the phosphorylation state of APC has never been analyzed directly. We show here that NGF- and EGF-induced initial cell extensions result in APC phosphorylation by the MAPK/ERK pathway, which, in parallel with inhibition of GSK-3β, promotes localization of APC to the tip of cell extensions. Whereas GSK-3β inhibition promotes APC binding and stabilization of microtubules, we show that phosphorylation by ERK inhibits the interaction of APC with F-actin, and APC-mediated F-actin bundling, but not APC-mediated microtubule bundling, in vitro. These results identify a previously unknown APC regulatory pathway during growth-factor-induced cell extension, and indicate that the GSK-3β and ERK pathways act in parallel to regulate interactions between APC and the cytoskeleton during the formation of cell extensions.
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34
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Kim SM, Bae J, Cho IH, Choi KY, Park YJ, Ryu JH, Chun JS, Song WK. Control of growth cone motility and neurite outgrowth by SPIN90. Exp Cell Res 2011; 317:2276-87. [PMID: 21763308 DOI: 10.1016/j.yexcr.2011.06.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 06/25/2011] [Accepted: 06/28/2011] [Indexed: 01/08/2023]
Abstract
SPIN90 is an F-actin binding protein thought to play important roles in regulating cytoskeletal dynamics. It is known that SPIN90 is expressed during the early stages of neuronal development, but details of its localization and function in growth cones have not been fully investigated. Our immunocytochemical data show that SPIN90 is enriched throughout growth cones and neuronal shafts in young hippocampal neurons. We also found that its localization correlates with and depends upon the presence of F-actin. Detailed observation of primary cultures of hippocampal neurons revealed that SPIN90 knockout reduces both growth cone areas and in the numbers of filopodia, as compared to wild-type neurons. In addition, total neurite length, the combined lengths of the longest (axonal) and shorter (dendritic) neurites, was smaller in SPIN90 knockout neurons than wild-type neurons. Finally, Cdc42 activity was down-regulated in SPIN90 knockout neurons. Taken together, our findings suggest that SPIN90 plays critical roles in controlling growth cone dynamics and neurite outgrowth.
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Affiliation(s)
- Seon-Myung Kim
- Cell Dynamics and Bioimaging Research Center, School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
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35
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Suter DM, Miller KE. The emerging role of forces in axonal elongation. Prog Neurobiol 2011; 94:91-101. [PMID: 21527310 DOI: 10.1016/j.pneurobio.2011.04.002] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2010] [Revised: 03/18/2011] [Accepted: 04/06/2011] [Indexed: 11/26/2022]
Abstract
An understanding of how axons elongate is needed to develop rational strategies to treat neurological diseases and nerve injury. Growth cone-mediated neuronal elongation is currently viewed as occurring through cytoskeletal dynamics involving the polymerization of actin and tubulin subunits at the tip of the axon. However, recent work suggests that axons and growth cones also generate forces (through cytoskeletal dynamics, kinesin, dynein, and myosin), forces induce axonal elongation, and axons lengthen by stretching. This review highlights results from various model systems (Drosophila, Aplysia, Xenopus, chicken, mouse, rat, and PC12 cells), supporting a role for forces, bulk microtubule movements, and intercalated mass addition in the process of axonal elongation. We think that a satisfying answer to the question, "How do axons grow?" will come by integrating the best aspects of biophysics, genetics, and cell biology.
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Affiliation(s)
- Daniel M Suter
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2054, United States.
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36
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Dent EW, Gupton SL, Gertler FB. The growth cone cytoskeleton in axon outgrowth and guidance. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a001800. [PMID: 21106647 DOI: 10.1101/cshperspect.a001800] [Citation(s) in RCA: 412] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Axon outgrowth and guidance to the proper target requires the coordination of filamentous (F)-actin and microtubules (MTs), the dynamic cytoskeletal polymers that promote shape change and locomotion. Over the past two decades, our knowledge of the many guidance cues, receptors, and downstream signaling cascades involved in neuronal outgrowth and guidance has increased dramatically. Less is known, however, about how those cascades of information converge and direct appropriate remodeling and interaction of cytoskeletal polymers, the ultimate effectors of movement and guidance. During development, much of the communication that occurs between environmental guidance cues and the cytoskeleton takes place at the growing tip of the axon, the neuronal growth cone. Several articles on this topic focus on the "input" to the growth cone, the myriad of receptor types, and their corresponding cognate ligands. Others investigate the signaling cascades initiated by receptors and propagated by second messenger pathways (i.e., kinases, phosphatases, GTPases). Ultimately, this plethora of information converges on proteins that associate directly with the actin and microtubule cytoskeletons. The role of these cytoskeletal-associated proteins, as well as the cytoskeleton itself in axon outgrowth and guidance, is the subject of this article.
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Affiliation(s)
- Erik W Dent
- Department of Anatomy, University of Wisconsin-Madison, 53706, USA
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37
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Abstract
In the body, cells encounter a complex milieu of signals, including topographical cues, in the form of the physical features of their surrounding environment. Imposed topography can affect cells on surfaces by promoting adhesion, spreading, alignment, morphological changes, and changes in gene expression. Neural response to topography is complex, and it depends on the dimensions and shapes of physical features. Looking toward repair of nerve injuries, strategies are being explored to engineer guidance conduits with precise surface topographies. How neurons and other cell types sense and interpret topography remains to be fully elucidated. Studies reviewed here include those of topography on cellular organization and function as well as potential cellular mechanisms of response.
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Affiliation(s)
- Diane Hoffman-Kim
- Center for Biomedical Engineering and Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA.
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38
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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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39
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Abstract
Axons follow highly stereotyped and reproducible trajectories to their targets. In this review we address the properties of the first pioneer neurons to grow in the developing nervous system and what has been learned over the past several decades about the extracellular and cell surface substrata on which axons grow. We then discuss the types of guidance cues and their receptors that influence axon extension, what determines where cues are expressed, and how axons respond to the cues they encounter in their environment.
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Affiliation(s)
- Jonathan Raper
- Department of Neurosciences, University of Pennsylvania, School of Medicine, Philadelphia, Pennsylvania 19104-6058, USA.
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40
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Abstract
Interactions between dynamic microtubules and actin filaments are essential to a wide range of cell biological processes including cell division, motility and morphogenesis. In neuronal growth cones, interactions between microtubules and actin filaments in filopodia are necessary for growth cones to make a turn. Growth-cone turning is a fundamental behaviour during axon guidance, as correct navigation of the growth cone through the embryo is required for it to locate an appropriate synaptic partner. Microtubule-actin filament interactions also occur in the transition zone and central domain of the growth cone, where actin arcs exert compressive forces to corral microtubules into the core of the growth cone and thereby facilitate microtubule bundling, a requirement for axon formation. We now have a fairly comprehensive understanding of the dynamic behaviour of the cytoskeleton in growth cones, and the stage is set for discovering the molecular machinery that enables microtubule-actin filament coupling in growth cones, as well as the intracellular signalling pathways that regulate these interactions. Furthermore, recent experiments suggest that microtubule-actin filament interactions might also be important for the formation of dendritic spines from filopodia in mature neurons. Therefore, the mechanisms coupling microtubules to actin filaments in growth-cone turning and dendritic-spine maturation might be conserved.
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Affiliation(s)
- Sara Geraldo
- The MRC Centre for Developmental Neurobiology, New Hunts House, Guy's Campus, King's College London, London SE1 1UL, UK
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41
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Shintani T, Ihara M, Tani S, Sakuraba J, Sakuta H, Noda M. APC2 plays an essential role in axonal projections through the regulation of microtubule stability. J Neurosci 2009; 29:11628-40. [PMID: 19759310 PMCID: PMC6665762 DOI: 10.1523/jneurosci.2394-09.2009] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Revised: 07/23/2009] [Accepted: 08/05/2009] [Indexed: 01/04/2023] Open
Abstract
Growth cones at the tip of growing axons are key cellular structures that detect guidance cues and mediate axonal growth. An increasing number of studies have suggested that the dynamic regulation of microtubules in the growth cone plays an essential role in growth cone steering. The dynamic properties of microtubules are considered to be regulated by variegated cellular factors but, in particular, through microtubule-interacting proteins. Here, we examined the functional role of adenomatous polyposis coli-like molecule 2 (APC2) in the development of axonal projections by using the chick retinotectal topographic projection system. APC2 is preferentially expressed in the nervous system from early developmental stages through to adulthood. Immunohistochemical analysis revealed that APC2 is distributed along microtubules in growth cones as well as axon shafts of retinal axons. Overexpression of APC2 in cultured cells induced the stabilization of microtubules, whereas the knockdown of APC2 in chick retinas with specific short hairpin RNA reduced the stability of microtubules in retinal axons. APC2 knockdown retinal axons showed abnormal growth attributable to a reduced response to ephrin-A2 in vitro. Furthermore, they showed drastic alterations in retinotectal projections without making clear target zones in the tectum in vivo. These results suggest that APC2 plays a critical role in the development of the nervous system through the regulation of microtubule stability.
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Affiliation(s)
- Takafumi Shintani
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
- School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan
| | - Masaru Ihara
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
| | - Sachiko Tani
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
- School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan
| | - Juichi Sakuraba
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
- School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan
| | - Hiraki Sakuta
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
- School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan
| | - Masaharu Noda
- Division of Molecular Neurobiology, National Institute for Basic Biology, and
- School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan
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42
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PHR regulates growth cone pausing at intermediate targets through microtubule disassembly. J Neurosci 2009; 29:6593-8. [PMID: 19458229 DOI: 10.1523/jneurosci.1115-09.2009] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Axonal growth cones use intermediate targets to navigate in the developing nervous system. Encountering these sites is correlated with growth cone pausing. PHR (Phr1, Esrom, Highwire, RPM-1) is a large neuronal ubiquitin ligase that interacts with multiple signaling pathways. Mouse and zebrafish phr mutants have highly penetrant axon pathfinding defects at intermediate targets. Mouse phr mutants contain excessive microtubules in the growth cone, which has been attributed to upregulation of DLK/p38 signaling. Here, we ask whether this pathway and microtubule misregulation are indeed linked to guidance errors in the vertebrate brain, using the zebrafish. By live imaging, we show that loops form when microtubules retract without depolymerizing. JNK, but not p38, phosphorylation is increased in mutant growth cones. However microtubule looping cannot be suppressed by inhibiting JNK. The phr microtubule defect can be phenocopied by taxol, while microtubule destabilization in vitro using nocodazole prevents loop formation. Acute disruption in vivo with nocodazole suppresses the intermediate target guidance defect. Given that microtubule looping is associated with growth cone pausing, we propose that microtubule disassembly, mediated by PHR, is essential for exiting the paused state at intermediate targets.
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43
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Fuentes F, Arregui CO. Microtubule and cell contact dependency of ER-bound PTP1B localization in growth cones. Mol Biol Cell 2009; 20:1878-89. [PMID: 19158394 DOI: 10.1091/mbc.e08-07-0675] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
PTP1B is an ER-bound protein tyrosine phosphatase implied in the regulation of cell adhesion. Here we investigated mechanisms involved in the positioning and dynamics of PTP1B in axonal growth cones and evaluated the role of this enzyme in axons. In growth cones, PTP1B consistently localizes in the central domain, and occasionally at the peripheral region and filopodia. Live imaging of GFP-PTP1B reveals dynamic excursions of fingerlike processes within the peripheral region and filopodia. PTP1B and GFP-PTP1B colocalize with ER markers and coalign with microtubules at the peripheral region and redistribute to the base of the growth cone after treatment with nocodazole, a condition that is reversible. Growth cone contact with cellular targets is accompanied by invasion of PTP1B and stable microtubules in the peripheral region aligned with the contact axis. Functional impairment of PTP1B causes retardation of axon elongation, as well as reduction of growth cone filopodia lifetime and Src activity. Our results highlight the role of microtubules and cell contacts in the positioning of ER-bound PTP1B to the peripheral region of growth cones, which may be required for the positive role of PTP1B in axon elongation, filopodia stabilization, and Src activity.
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Affiliation(s)
- Federico Fuentes
- Instituto de Investigaciones Biotecnológicas, Universidad de San Martín, 1650 San Martín, Buenos Aires, Argentina
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44
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Garcia-Marin V, Garcia-Lopez P, Freire M. The growth cone as seen through Cajal's original histological preparations and publications. JOURNAL OF THE HISTORY OF THE NEUROSCIENCES 2009; 18:197-210. [PMID: 19367487 DOI: 10.1080/09647040801961430] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
During the development of the nervous system, each neuron must contact its appropriate target cell in order to establish its specific connections. More than a century ago, Ramon y Cajal discovered an amoeboid-like structure at the end of the axon of developing nerve cells. He called this structure the growth cone [cono de crecimiento] and he proposed that this structure was guided towards its target tissue by chemical substances secreted by the different cells that line its course. We have reviewed the discovery of the growth cone by Cajal using his original publications, his original scientific drawings, and by studying his histological preparations conserved at the "Instituto Cajal" (Madrid, Spain).(1) We found a very good correlation between the structure of the growth cone in the Golgi-impregnated and reduced silver-nitrate-stained material used by Cajal, and that which is revealed with present-day methods. Finally, Cajal's view of the function of the growth cone and his chemotactic hypothesis will also be considered in the light of present-day knowledge.
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Lee AC, Suter DM. Quantitative analysis of microtubule dynamics during adhesion-mediated growth cone guidance. Dev Neurobiol 2008; 68:1363-77. [PMID: 18698606 DOI: 10.1002/dneu.20662] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
During adhesion-mediated neuronal growth cone guidance microtubules undergo major rearrangements. However, it is unknown whether microtubules extend to adhesion sites because of changes in plus-end polymerization and/or translocation dynamics, because of changes in actin-microtubule interactions, or because they follow the reorganization of the actin cytoskeleton. Here, we used fluorescent speckle microscopy to directly quantify microtubule and actin dynamics in Aplysia growth cones as they turn towards beads coated with the cell adhesion molecule apCAM. During the initial phase of adhesion formation, dynamic microtubules in the peripheral domain preferentially explore apCAM-beads prior to changes in growth cone morphology and retrograde actin flow. Interestingly, these early microtubules have unchanged polymerization rates but spend less time in retrograde translocation due to uncoupling from actin flow. Furthermore, microtubules exploring the adhesion site spend less time in depolymerization. During the later phase of traction force generation, the central domain advances and more microtubules in the peripheral domain extend because of attenuation of actin flow and clearance of F-actin structures. Microtubules in the transition zone and central domain, however, translocate towards the adhesion site in concert with actin arcs and bundles, respectively. We conclude that adhesion molecules guide neuronal growth cones and underlying microtubule rearrangements largely by differentially regulating microtubule-actin coupling and actin movements according to growth cone region and not by controlling plus-end polymerization rates.
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Affiliation(s)
- Aih Cheun Lee
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
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Axon guidance: asymmetric signaling orients polarized outgrowth. Trends Cell Biol 2008; 18:597-603. [PMID: 18951796 DOI: 10.1016/j.tcb.2008.09.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Revised: 09/25/2008] [Accepted: 09/26/2008] [Indexed: 11/22/2022]
Abstract
A network of connections is established as neural circuits form between neurons. To make these connections, neurons initiate asymmetric axon outgrowth in response to extracellular guidance cues. Within the specialized growth cones of migrating axons, F-actin and microtubules asymmetrically accumulate where an axon projects forward. Although many guidance cues, receptors and intracellular signaling components that are required for axon guidance have been identified, the means by which the asymmetry is established and maintained is unclear. Here, we discuss recent studies in invertebrate and vertebrate organisms that define a signaling module comprising UNC-6 (the Caenorhabditis elegans ortholog of netrin), UNC-40 (the C. elegans ortholog of DCC), PI3K, Rac and MIG-10 (the C. elegans ortholog of lamellipodin) and we consider how this module could establish polarized outgrowth in response to guidance cues.
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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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Quinn CC, Pfeil DS, Wadsworth WG. CED-10/Rac1 mediates axon guidance by regulating the asymmetric distribution of MIG-10/lamellipodin. Curr Biol 2008; 18:808-13. [PMID: 18499456 DOI: 10.1016/j.cub.2008.04.050] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Revised: 03/21/2008] [Accepted: 04/22/2008] [Indexed: 11/28/2022]
Abstract
Axon migrations are guided by extracellular cues that induce asymmetric outgrowth activity in the growth cone. Several intracellular signaling proteins have been implicated in the guidance response. However, how these proteins interact to generate asymmetric outgrowth activity is unknown. Here, we present evidence that in C. elegans, the CED-10/Rac1 GTPase binds to and causes asymmetric localization of MIG-10/lamellipodin, a protein that regulates actin polymerization and has outgrowth-promoting activity in neurons. Genetic analysis indicates that mig-10 and ced-10 function together to orient axon outgrowth. The RAPH domain of MIG-10 binds to activated CED-10/Rac1, and ced-10 function is required for the asymmetric MIG-10 localization that occurs in response to the UNC-6/netrin guidance cue. We also show that asymmetric localization of MIG-10 in growth cones is associated with asymmetric concentrations of f-actin and microtubules. These results suggest that CED-10/Rac1 is asymmetrically activated in response to the UNC-6/netrin signal and thereby causes asymmetric recruitment of MIG-10/lamellipodin. We propose that the interaction between activated CED-10/Rac1 and MIG-10/lamellipodin triggers local cytoskeletal assembly and polarizes outgrowth activity in response to UNC-6/netrin.
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Affiliation(s)
- Christopher C Quinn
- Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5653, USA.
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Xie J, Chen L, Varadan VK, Yancey J, Srivatsan M. The effects of functional magnetic nanotubes with incorporated nerve growth factor in neuronal differentiation of PC12 cells. NANOTECHNOLOGY 2008; 19:105101. [PMID: 21817692 DOI: 10.1088/0957-4484/19/10/105101] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this in vitro study the efficiency of magnetic nanotubes to bind with nerve growth factor (NGF) and the ability of NGF-incorporated magnetic nanotubes to release the bound NGF are investigated using rat pheochromocytoma cells (PC12 cells). It is found that functional magnetic nanotubes with NGF incorporation enabled the differentiation of PC12 cells into neurons exhibiting growth cones and neurite outgrowth. Microscope observations show that filopodia extending from neuron growth cones were in close proximity to the NGF-incorporated magnetic nanotubes, at times appearing to extend towards or into them. These results show that magnetic nanotubes can be used as a delivery vehicle for NGF and thus may be exploited in attempts to treat neurodegenerative disorders such as Parkinson's disease with neurotrophins. Further neurite outgrowth can be controlled by manipulating magnetic nanotubes with external magnetic fields, thus helping in directed regeneration.
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Affiliation(s)
- Jining Xie
- Nanomaterials and Nanotubes Research Laboratory, College of Engineering, University of Arkansas, Fayetteville, AR 72701, USA
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Hlady V, Hodgkinson G. The effects of proteoglycan surface patterning on neuronal pathfinding. MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK 2007; 38:975. [PMID: 20119506 PMCID: PMC2813059 DOI: 10.1002/mawe.200700224] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2007] [Indexed: 05/28/2023]
Abstract
Protein micropatterning techniques are increasingly applied in cell choice assays to investigate fundamental biological phenomena that contribute to the host response to implanted biomaterials, and to explore the effects of protein stability and biological activity on cell behavior for in vitro cell studies. In the area of neuronal regeneration the protein micropatterning and cell choice assays are used to improve our understanding of the mechanisms directing nervous system during development and regenerative failure in the central nervous system (CNS) wound healing environment. In these cell assays, protein micropatterns need to be characterized for protein stability, bioactivity, and spatial distribution and then correlated with observed mammalian cell behavior using appropriate model system for CNS development and repair. This review provides the background on protein micropatterning for cell choice assays and describes some novel patterns that were developed to interrogate neuronal adaptation to inhibitory signals encountered in CNS injuries.
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Affiliation(s)
- V. Hlady
- University of Utah, Salt Lake City, UT 83112, USA
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