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Abstract
Dendrite branching is an essential process for building complex nervous systems. It determines the number, distribution and integration of inputs into a neuron, and is regulated to create the diverse dendrite arbor branching patterns characteristic of different neuron types. The microtubule cytoskeleton is critical to provide structure and exert force during dendrite branching. It also supports the functional requirements of dendrites, reflected by differential microtubule architectural organization between neuron types, illustrated here for sensory neurons. Both anterograde and retrograde microtubule polymerization occur within growing dendrites, and recent studies indicate that branching is enhanced by anterograde microtubule polymerization events in nascent branches. The polarities of microtubule polymerization events are regulated by the position and orientation of microtubule nucleation events in the dendrite arbor. Golgi outposts are a primary microtubule nucleation center in dendrites and share common nucleation machinery with the centrosome. In addition, pre-existing dendrite microtubules may act as nucleation sites. We discuss how balancing the activities of distinct nucleation machineries within the growing dendrite can alter microtubule polymerization polarity and dendrite branching, and how regulating this balance can generate neuron type-specific morphologies.
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Affiliation(s)
- Caroline Delandre
- a Laboratory for Genetic Control of Neuronal Architecture, RIKEN Brain Science Institute , Wako , Saitama , Japan
| | - Reiko Amikura
- a Laboratory for Genetic Control of Neuronal Architecture, RIKEN Brain Science Institute , Wako , Saitama , Japan
| | - Adrian W Moore
- a Laboratory for Genetic Control of Neuronal Architecture, RIKEN Brain Science Institute , Wako , Saitama , Japan
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402
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403
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Eira J, Silva CS, Sousa MM, Liz MA. The cytoskeleton as a novel therapeutic target for old neurodegenerative disorders. Prog Neurobiol 2016; 141:61-82. [PMID: 27095262 DOI: 10.1016/j.pneurobio.2016.04.007] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Revised: 04/13/2016] [Accepted: 04/13/2016] [Indexed: 12/12/2022]
Abstract
Cytoskeleton defects, including alterations in microtubule stability, in axonal transport as well as in actin dynamics, have been characterized in several unrelated neurodegenerative conditions. These observations suggest that defects of cytoskeleton organization may be a common feature contributing to neurodegeneration. In line with this hypothesis, drugs targeting the cytoskeleton are currently being tested in animal models and in human clinical trials, showing promising effects. Drugs that modulate microtubule stability, inhibitors of posttranslational modifications of cytoskeletal components, specifically compounds affecting the levels of tubulin acetylation, and compounds targeting signaling molecules which regulate cytoskeleton dynamics, constitute the mostly addressed therapeutic interventions aiming at preventing cytoskeleton damage in neurodegenerative disorders. In this review, we will discuss in a critical perspective the current knowledge on cytoskeleton damage pathways as well as therapeutic strategies designed to revert cytoskeleton-related defects mainly focusing on the following neurodegenerative disorders: Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis and Charcot-Marie-Tooth Disease.
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Affiliation(s)
- Jessica Eira
- Neurodegeneration Group, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200 Porto, Portugal
| | - Catarina Santos Silva
- Neurodegeneration Group, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200 Porto, Portugal
| | - Mónica Mendes Sousa
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200 Porto, Portugal; Nerve Regeneration Group, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200 Porto, Portugal
| | - Márcia Almeida Liz
- Neurodegeneration Group, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200 Porto, Portugal.
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404
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Ti SC, Pamula MC, Howes SC, Duellberg C, Cade NI, Kleiner RE, Forth S, Surrey T, Nogales E, Kapoor TM. Mutations in Human Tubulin Proximal to the Kinesin-Binding Site Alter Dynamic Instability at Microtubule Plus- and Minus-Ends. Dev Cell 2016; 37:72-84. [PMID: 27046833 PMCID: PMC4832424 DOI: 10.1016/j.devcel.2016.03.003] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 02/12/2016] [Accepted: 03/04/2016] [Indexed: 01/10/2023]
Abstract
The assembly of microtubule-based cellular structures depends on regulated tubulin polymerization and directional transport. Here, we purify and characterize tubulin heterodimers that have human β-tubulin isotype III (TUBB3), as well as heterodimers with one of two β-tubulin mutations (D417H or R262H). Both point mutations are proximal to the kinesin-binding site and have been linked to an ocular motility disorder in humans. Compared to wild-type, microtubules with these mutations have decreased catastrophe frequencies and increased average lifetimes of plus- and minus-end-stabilizing caps. Importantly, the D417H mutation does not alter microtubule lattice structure or Mal3 binding to growing filaments. Instead, this mutation reduces the affinity of tubulin for TOG domains and colchicine, suggesting that the distribution of tubulin heterodimer conformations is changed. Together, our findings reveal how residues on the surface of microtubules, distal from the GTP-hydrolysis site and inter-subunit contacts, can alter polymerization dynamics at the plus- and minus-ends of microtubules.
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Affiliation(s)
- Shih-Chieh Ti
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Melissa C Pamula
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Stuart C Howes
- Biophysics Graduate Group, University of California, Berkeley, CA 94720, USA
| | - Christian Duellberg
- The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London WC2A 3LY, UK
| | - Nicholas I Cade
- The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London WC2A 3LY, UK
| | - Ralph E Kleiner
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Scott Forth
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Thomas Surrey
- The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London WC2A 3LY, UK
| | - Eva Nogales
- Life Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California Berkeley, Berkeley, CA 94720, USA
| | - Tarun M Kapoor
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
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405
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Britt DJ, Farías GG, Guardia CM, Bonifacino JS. Mechanisms of Polarized Organelle Distribution in Neurons. Front Cell Neurosci 2016; 10:88. [PMID: 27065809 PMCID: PMC4814528 DOI: 10.3389/fncel.2016.00088] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 03/21/2016] [Indexed: 01/10/2023] Open
Abstract
Neurons are highly polarized cells exhibiting axonal and somatodendritic domains with distinct complements of cytoplasmic organelles. Although some organelles are widely distributed throughout the neuronal cytoplasm, others are segregated to either the axonal or somatodendritic domains. Recent findings show that organelle segregation is largely established at a pre-axonal exclusion zone (PAEZ) within the axon hillock. Polarized sorting of cytoplasmic organelles at the PAEZ is proposed to depend mainly on their selective association with different microtubule motors and, in turn, with distinct microtubule arrays. Somatodendritic organelles that escape sorting at the PAEZ can be subsequently retrieved at the axon initial segment (AIS) by a microtubule- and/or actin-based mechanism. Dynamic sorting along the PAEZ-AIS continuum can thus explain the polarized distribution of cytoplasmic organelles between the axonal and somatodendritic domains.
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Affiliation(s)
- Dylan J Britt
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
| | - Ginny G Farías
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
| | - Carlos M Guardia
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
| | - Juan S Bonifacino
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
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406
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López-Benito S, Lillo C, Hernández-Hernández Á, Chao MV, Arévalo JC. ARMS/Kidins220 and synembryn-B levels regulate NGF-mediated secretion. J Cell Sci 2016; 129:1866-77. [PMID: 26966186 DOI: 10.1242/jcs.184168] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2015] [Accepted: 03/05/2016] [Indexed: 01/22/2023] Open
Abstract
Proper development of the nervous system requires a temporally and spatially orchestrated set of events including differentiation, synapse formation and neurotransmission. Nerve growth factor (NGF) acting through the TrkA neurotrophin receptor (also known as NTRK1) regulates many of these events. However, the molecular mechanisms responsible for NGF-regulated secretion are not completely understood. Here, we describe a new signaling pathway involving TrkA, ARMS (also known as Kidins220), synembryn-B and Rac1 in NGF-mediated secretion in PC12 cells. Whereas overexpression of ARMS blocked NGF-mediated secretion, without affecting basal secretion, a decrease in ARMS resulted in potentiation. Similar effects were observed with synembryn-B, a protein that interacts directly with ARMS. Downstream of ARMS and synembryn-B are Gαq and Trio proteins, which modulate the activity of Rac1 in response to NGF. Expression of dominant-negative Rac1 rescued the secretion defects of cells overexpressing ARMS or synembryn-B. Thus, this neurotrophin pathway represents a new mechanism responsible for NGF-regulated secretion.
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Affiliation(s)
- Saray López-Benito
- Department of Cell Biology and Pathology, Instituto de Neurociencias de Castilla y León (INCyL), University of Salamanca, Salamanca 37007, Spain Institute of Biomedical Research of Salamanca (IBSAL), Salamanca 37007, Spain
| | - Concepción Lillo
- Department of Cell Biology and Pathology, Instituto de Neurociencias de Castilla y León (INCyL), University of Salamanca, Salamanca 37007, Spain Institute of Biomedical Research of Salamanca (IBSAL), Salamanca 37007, Spain
| | - Ángel Hernández-Hernández
- Institute of Biomedical Research of Salamanca (IBSAL), Salamanca 37007, Spain Department of Biochemistry and Molecular Biology, University of Salamanca, Salamanca 37007, Spain
| | - Moses V Chao
- Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, Departments of Cell Biology, Physiology and Neuroscience, Psychiatry, and Neural Sciences, New York University School of Medicine, New York, NY 10016, USA
| | - Juan C Arévalo
- Department of Cell Biology and Pathology, Instituto de Neurociencias de Castilla y León (INCyL), University of Salamanca, Salamanca 37007, Spain Institute of Biomedical Research of Salamanca (IBSAL), Salamanca 37007, Spain
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407
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Barnhart EL. Mechanics of mitochondrial motility in neurons. Curr Opin Cell Biol 2016; 38:90-9. [DOI: 10.1016/j.ceb.2016.02.022] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 02/18/2016] [Accepted: 02/25/2016] [Indexed: 11/17/2022]
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408
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Kneussel M, Hausrat TJ. Postsynaptic Neurotransmitter Receptor Reserve Pools for Synaptic Potentiation. Trends Neurosci 2016; 39:170-182. [PMID: 26833258 DOI: 10.1016/j.tins.2016.01.002] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 01/06/2016] [Accepted: 01/07/2016] [Indexed: 11/18/2022]
Abstract
At excitatory and inhibitory synapses, an immediate transfer of additional neurotransmitter receptors from non-synaptic positions to the synapse mediates synaptic long-term potentiation (LTP). Different types of non-synaptic reserve pools permit the rapid supply of transmembrane neurotransmitter receptors. Recycling endosomes (REs) serve as an intracellular reservoir of receptors that is delivered to the plasma membrane on LTP induction. Furthermore, AMPA receptors at the non-synaptic plasma membrane provide an extrasynaptic reserve pool that is also important to potentiate synapse function. Finally, bidirectional synaptic versus extrasynaptic trapping of freely diffusing plasma membrane GABAA receptors (GABAARs) by scaffolding proteins modulates synaptic transmission. Here we discuss novel findings regarding neurotransmitter receptor reservoirs and potential reserve pool mechanisms for synaptic potentiation.
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Affiliation(s)
- Matthias Kneussel
- Department of Molecular Neurogenetics, Center for Molecular Neurobiology, ZMNH, University Medical Center Hamburg-Eppendorf, Falkenried 94, 20251 Hamburg, Germany.
| | - Torben Johann Hausrat
- Department of Molecular Neurogenetics, Center for Molecular Neurobiology, ZMNH, University Medical Center Hamburg-Eppendorf, Falkenried 94, 20251 Hamburg, Germany
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409
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Yau KW, Schätzle P, Tortosa E, Pagès S, Holtmaat A, Kapitein LC, Hoogenraad CC. Dendrites In Vitro and In Vivo Contain Microtubules of Opposite Polarity and Axon Formation Correlates with Uniform Plus-End-Out Microtubule Orientation. J Neurosci 2016. [PMID: 26818498 DOI: 10.1523/jneurosci.2430-15.20166] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2023] Open
Abstract
UNLABELLED In cultured vertebrate neurons, axons have a uniform arrangement of microtubules with plus-ends distal to the cell body (plus-end-out), whereas dendrites contain mixed polarity orientations with both plus-end-out and minus-end-out oriented microtubules. Rather than non-uniform microtubules, uniparallel minus-end-out microtubules are the signature of dendrites in Drosophila and Caenorhabditis elegans neurons. To determine whether mixed microtubule organization is a conserved feature of vertebrate dendrites, we used live-cell imaging to systematically analyze microtubule plus-end orientations in primary cultures of rat hippocampal and cortical neurons, dentate granule cells in mouse organotypic slices, and layer 2/3 pyramidal neurons in the somatosensory cortex of living mice. In vitro and in vivo, all microtubules had a plus-end-out orientation in axons, whereas microtubules in dendrites had mixed orientations. When dendritic microtubules were severed by laser-based microsurgery, we detected equal numbers of plus- and minus-end-out microtubule orientations throughout the dendritic processes. In dendrites, the minus-end-out microtubules were generally more stable and comparable with plus-end-out microtubules in axons. Interestingly, at early stages of neuronal development in nonpolarized cells, newly formed neurites already contained microtubules of opposite polarity, suggesting that the establishment of uniform plus-end-out microtubules occurs during axon formation. We propose a model in which the selective formation of uniform plus-end-out microtubules in the axon is a critical process underlying neuronal polarization. SIGNIFICANCE STATEMENT Live-cell imaging was used to systematically analyze microtubule organization in primary cultures of rat hippocampal neurons, dentate granule cells in mouse organotypic slices, and layer 2/3 pyramidal neuron in somatosensory cortex of living mice. In vitro and in vivo, all microtubules have a plus-end-out orientation in axons, whereas microtubules in dendrites have mixed orientations. Interestingly, newly formed neurites of nonpolarized neurons already contain mixed microtubules, and the specific organization of uniform plus-end-out microtubules only occurs during axon formation. Based on these findings, the authors propose a model in which the selective formation of uniform plus-end-out microtubules in the axon is a critical process underlying neuronal polarization.
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Affiliation(s)
- Kah Wai Yau
- Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and
| | - Philipp Schätzle
- Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and
| | - Elena Tortosa
- Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and
| | - Stéphane Pagès
- Department of Basic Neurosciences, Faculty of Medicine and the Center for Neuroscience, University of Geneva, 1211 Geneva, Switzerland
| | - Anthony Holtmaat
- Department of Basic Neurosciences, Faculty of Medicine and the Center for Neuroscience, University of Geneva, 1211 Geneva, Switzerland
| | - Lukas C Kapitein
- Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and
| | - Casper C Hoogenraad
- Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and
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410
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411
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del Castillo U, Winding M, Lu W, Gelfand VI. Interplay between kinesin-1 and cortical dynein during axonal outgrowth and microtubule organization in Drosophila neurons. eLife 2015; 4:e10140. [PMID: 26615019 PMCID: PMC4739764 DOI: 10.7554/elife.10140] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 11/27/2015] [Indexed: 12/21/2022] Open
Abstract
In this study, we investigated how microtubule motors organize microtubules in Drosophila neurons. We showed that, during the initial stages of axon outgrowth, microtubules display mixed polarity and minus-end-out microtubules push the tip of the axon, consistent with kinesin-1 driving outgrowth by sliding antiparallel microtubules. At later stages, the microtubule orientation in the axon switches from mixed to uniform polarity with plus-end-out. Dynein knockdown prevents this rearrangement and results in microtubules of mixed orientation in axons and accumulation of microtubule minus-ends at axon tips. Microtubule reorganization requires recruitment of dynein to the actin cortex, as actin depolymerization phenocopies dynein depletion, and direct recruitment of dynein to the membrane bypasses the actin requirement. Our results show that cortical dynein slides ‘minus-end-out’ microtubules from the axon, generating uniform microtubule arrays. We speculate that differences in microtubule orientation between axons and dendrites could be dictated by differential activity of cortical dynein. DOI:http://dx.doi.org/10.7554/eLife.10140.001 Motor proteins can move along filaments called microtubules to transport proteins and other materials to different parts of the cell. Microtubules are “polar” filaments, meaning that they have two distinct ends that have different chemical properties. Motor proteins can only move along these filaments in one direction, for example, the kinesin motor proteins generally move toward the so-called “plus-end”, while dynein motors move in the opposite direction. A typical nerve cell (or neuron) is composed of a cell body, a long projection called an axon and many small branch-like structures called dendrites. Within the axon, the microtubules are arranged so that their plus-ends point outwards, but the microtubules in dendrites are arranged differently so that many minus-ends point outwards instead. This polarity is important for the neuron in deciding which proteins should be transported to axons, and which should go to the dendrites. However, it is not clear how these different microtubule arrangements are established. Here, del Castillo et al. used microscopy to study microtubules in the axons of fruit fly neurons. The experiments show that in the very early stages of neuron development, the axons contained microtubules of mixed polarity. However, by the later stages, the microtubules had become uniform with all the plus-ends directed outwards. Further experiments show that dynein is responsible for this organization as it pushes the minus-end-out microtubules out of the axons. Dynein uses a scaffold made of a protein called actin to attach to the inner surface of the cell and move the minus-end microtubules to the cell body of the neuron. Thus, del Castillo et al.’s findings reveal that these dynein motors are responsible for the polarity of microtubules in mature axons. The next challenge is to understand how dynein is attached to the actin scaffold and why it rearranges microtubules in axons, but not in dendrites. DOI:http://dx.doi.org/10.7554/eLife.10140.002
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Affiliation(s)
- Urko del Castillo
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - Michael Winding
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - Wen Lu
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, United States
| | - Vladimir I Gelfand
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, United States
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412
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Haase G, Rabouille C. Golgi Fragmentation in ALS Motor Neurons. New Mechanisms Targeting Microtubules, Tethers, and Transport Vesicles. Front Neurosci 2015; 9:448. [PMID: 26696811 PMCID: PMC4672084 DOI: 10.3389/fnins.2015.00448] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 11/13/2015] [Indexed: 12/12/2022] Open
Abstract
Pathological alterations of the Golgi apparatus, such as its fragmentation represent an early pre-clinical feature of many neurodegenerative diseases and have been widely studied in the motor neuron disease amyotrophic lateral sclerosis (ALS). Yet, the underlying molecular mechanisms have remained cryptic. In principle, Golgi fragmentation may result from defects in three major classes of proteins: structural Golgi proteins, cytoskeletal proteins and molecular motors, as well as proteins mediating transport to and through the Golgi. Here, we present the different mechanisms that may underlie Golgi fragmentation in animal and cellular models of ALS linked to mutations in SOD1, TARDBP (TDP-43), VAPB, and C9Orf72 and we propose a novel one based on findings in progressive motor neuronopathy (pmn) mice. These mice are mutated in the TBCE gene encoding the cis-Golgi localized tubulin-binding cofactor E, one of five chaperones that assist in tubulin folding and microtubule polymerization. Loss of TBCE leads to alterations in Golgi microtubules, which in turn impedes on the maintenance of the Golgi architecture. This is due to down-regulation of COPI coat components, dispersion of Golgi tethers and strong accumulation of ER-Golgi SNAREs. These effects are partially rescued by the GTPase ARF1 through recruitment of TBCE to the Golgi. We hypothesize that defects in COPI vesicles, microtubules and their interaction may also underlie Golgi fragmentation in human ALS linked to other mutations, spinal muscular atrophy (SMA), and related motor neuron diseases. We also discuss the functional relevance of pathological Golgi alterations, in particular their potential causative, contributory, or compensatory role in the degeneration of motor neuron cell bodies, axons and synapses.
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Affiliation(s)
- Georg Haase
- Centre National de la Recherche Scientifique and Aix-Marseille Université UMR 7289, Institut de Neurosciences de la Timone Marseille, France
| | - Catherine Rabouille
- The Department of Cell Biology, Hubrecht Institute of the Royal Netherlands Academy of Arts and Sciences and University Medical Center Utrecht Utrecht, Netherlands
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413
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Jakobs M, Franze K, Zemel A. Force Generation by Molecular-Motor-Powered Microtubule Bundles; Implications for Neuronal Polarization and Growth. Front Cell Neurosci 2015; 9:441. [PMID: 26617489 PMCID: PMC4639704 DOI: 10.3389/fncel.2015.00441] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 10/26/2015] [Indexed: 11/16/2022] Open
Abstract
The heavily cross-linked microtubule (MT) bundles found in neuronal processes play a central role in the initiation, growth and maturation of axons and dendrites; however, a quantitative understanding of their mechanical function is still lacking. We here developed computer simulations to investigate the dynamics of force generation in 1D bundles of MTs that are cross-linked and powered by molecular motors. The motion of filaments and the forces they exert are investigated as a function of the motor type (unipolar or bipolar), MT density and length, applied load, and motor connectivity. We demonstrate that only unipolar motors (e.g., kinesin-1) can provide the driving force for bundle expansion, while bipolar motors (e.g., kinesin-5) oppose it. The force generation capacity of the bundles is shown to depend sharply on the fraction of unipolar motors due to a percolation transition that must occur in the bundle. Scaling laws between bundle length, force, MT length and motor fraction are presented. In addition, we investigate the dynamics of growth in the presence of a constant influx of MTs. Beyond a short equilibration period, the bundles grow linearly in time. In this growth regime, the bundle extends as one mass forward with most filaments sliding with the growth velocity. The growth velocity is shown to be dictated by the inward flux of MTs, to inversely scale with the load and to be independent of the free velocity of the motors. These findings provide important molecular-level insights into the mechanical function of the MT cytoskeleton in normal axon growth and regeneration after injury.
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Affiliation(s)
- Maximilian Jakobs
- Department of Physiology, Development and Neuroscience, University of CambridgeCambridge, UK
- Bonn Cologne Graduate School of Physics and Astronomy, University of CologneCologne, Germany
| | - Kristian Franze
- Department of Physiology, Development and Neuroscience, University of CambridgeCambridge, UK
| | - Assaf Zemel
- Institute of Dental Sciences and Fritz Haber Research Center for Molecular Dynamics, Hebrew University of JerusalemJerusalem, Israel
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414
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Jaarsma D, Hoogenraad CC. Cytoplasmic dynein and its regulatory proteins in Golgi pathology in nervous system disorders. Front Neurosci 2015; 9:397. [PMID: 26578860 PMCID: PMC4620150 DOI: 10.3389/fnins.2015.00397] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 10/09/2015] [Indexed: 12/15/2022] Open
Abstract
The Golgi apparatus is a dynamic organelle involved in processing and sorting of lipids and proteins. In neurons, the Golgi apparatus is important for the development of axons and dendrites and maintenance of their highly complex polarized morphology. The motor protein complex cytoplasmic dynein has an important role in Golgi apparatus positioning and function. Together, with dynactin and other regulatory factors it drives microtubule minus-end directed motility of Golgi membranes. Inhibition of dynein results in fragmentation and dispersion of the Golgi ribbon in the neuronal cell body, resembling the Golgi abnormalities observed in some neurodegenerative disorders, in particular motor neuron diseases. Mutations in dynein and its regulatory factors, including the dynactin subunit p150Glued, BICD2 and Lis-1, are associated with several human nervous system disorders, including cortical malformation and motor neuropathy. Here we review the role of dynein and its regulatory factors in Golgi function and positioning, and the potential role of dynein malfunction in causing Golgi apparatus abnormalities in nervous system disorders.
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Affiliation(s)
- Dick Jaarsma
- Department of Neuroscience, Erasmus MC Rotterdam, Netherlands
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