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Kotaich F, Caillol D, Bomont P. Neurofilaments in health and Charcot-Marie-Tooth disease. Front Cell Dev Biol 2023; 11:1275155. [PMID: 38164457 PMCID: PMC10758125 DOI: 10.3389/fcell.2023.1275155] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 10/02/2023] [Indexed: 01/03/2024] Open
Abstract
Neurofilaments (NFs) are the most abundant component of mature neurons, that interconnect with actin and microtubules to form the cytoskeleton. Specifically expressed in the nervous system, NFs present the particularity within the Intermediate Filament family of being formed by four subunits, the neurofilament light (NF-L), medium (NF-M), heavy (NF-H) proteins and α-internexin or peripherin. Here, we review the current knowledge on NF proteins and neurofilaments, from their domain structures and their model of assembly to the dynamics of their transport and degradation along the axon. The formation of the filament and its behaviour are regulated by various determinants, including post-transcriptional (miRNA and RBP proteins) and post-translational (phosphorylation and ubiquitination) modifiers. Altogether, the complex set of modifications enable the neuron to establish a stable but elastic NF array constituting the structural scaffold of the axon, while permitting the local expression of NF proteins and providing the dynamics necessary to fulfil local demands and respond to stimuli and injury. Thus, in addition to their roles in mechano-resistance, radial axonal outgrowth and nerve conduction, NFs control microtubule dynamics, organelle distribution and neurotransmission at the synapse. We discuss how the studies of neurodegenerative diseases with NF aggregation shed light on the biology of NFs. In particular, the NEFL and NEFH genes are mutated in Charcot-Marie-Tooth (CMT) disease, the most common inherited neurological disorder of the peripheral nervous system. The clinical features of the CMT forms (axonal CMT2E, CMT2CC; demyelinating CMT1F; intermediate I-CMT) with symptoms affecting the central nervous system (CNS) will allow us to further investigate the physiological roles of NFs in the brain. Thus, NF-CMT mouse models exhibit various degrees of sensory-motor deficits associated with CNS symptoms. Cellular systems brought findings regarding the dominant effect of NF-L mutants on NF aggregation and transport, although these have been recently challenged. Neurofilament detection without NF-L in recessive CMT is puzzling, calling for a re-examination of the current model in which NF-L is indispensable for NF assembly. Overall, we discuss how the fundamental and translational fields are feeding each-other to increase but also challenge our knowledge of NF biology, and to develop therapeutic avenues for CMT and neurodegenerative diseases with NF aggregation.
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Affiliation(s)
| | | | - Pascale Bomont
- ERC team, NeuroMyoGene Institute-Pathophysiology and Genetics of Neuron and Muscle, Inserm U1315, CNRS UMR5261, University of Lyon 1, Lyon, France
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Glomb O, Swaim G, Munoz LLancao P, Lovejoy C, Sutradhar S, Park J, Wu Y, Cason SE, Holzbaur ELF, Hammarlund M, Howard J, Ferguson SM, Gramlich MW, Yogev S. A kinesin-1 adaptor complex controls bimodal slow axonal transport of spectrin in Caenorhabditis elegans. Dev Cell 2023; 58:1847-1863.e12. [PMID: 37751746 PMCID: PMC10574138 DOI: 10.1016/j.devcel.2023.08.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Revised: 08/18/2023] [Accepted: 08/30/2023] [Indexed: 09/28/2023]
Abstract
An actin-spectrin lattice, the membrane periodic skeleton (MPS), protects axons from breakage. MPS integrity relies on spectrin delivery via slow axonal transport, a process that remains poorly understood. We designed a probe to visualize endogenous spectrin dynamics at single-axon resolution in vivo. Surprisingly, spectrin transport is bimodal, comprising fast runs and movements that are 100-fold slower than previously reported. Modeling and genetic analysis suggest that the two rates are independent, yet both require kinesin-1 and the coiled-coil proteins UNC-76/FEZ1 and UNC-69/SCOC, which we identify as spectrin-kinesin adaptors. Knockdown of either protein led to disrupted spectrin motility and reduced distal MPS, and UNC-76 overexpression instructed excessive transport of spectrin. Artificially linking spectrin to kinesin-1 drove robust motility but inefficient MPS assembly, whereas impairing MPS assembly led to excessive spectrin transport, suggesting a balance between transport and assembly. These results provide insight into slow axonal transport and MPS integrity.
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Affiliation(s)
- Oliver Glomb
- Department of Neuroscience, Yale School of Medicine, New Haven, CT 06510, USA
| | - Grace Swaim
- Department of Neuroscience, Yale School of Medicine, New Haven, CT 06510, USA; Department of Cell Biology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Pablo Munoz LLancao
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Christopher Lovejoy
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Sabyasachi Sutradhar
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06510, USA
| | - Junhyun Park
- Department of Neuroscience, Yale School of Medicine, New Haven, CT 06510, USA
| | - Youjun Wu
- Department of Genetics, Yale School of Medicine, New Haven, CT 06510, USA
| | - Sydney E Cason
- Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104, USA; Neuroscience Graduate Group, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Erika L F Holzbaur
- Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104, USA; Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Marc Hammarlund
- Department of Neuroscience, Yale School of Medicine, New Haven, CT 06510, USA; Department of Genetics, Yale School of Medicine, New Haven, CT 06510, USA
| | - Jonathon Howard
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06510, USA; Quantitative Biology Institute, Yale University, New Haven, CT 06510, USA
| | - Shawn M Ferguson
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06510, USA
| | | | - Shaul Yogev
- Department of Neuroscience, Yale School of Medicine, New Haven, CT 06510, USA.
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Kwong JMK, Caprioli J, Lee JCY, Song Y, Yu FJ, Bian J, Sze YH, Li KK, Do CW, To CH, Lam TC. Differential Responses of Retinal Neurons and Glia Revealed via Proteomic Analysis on Primary and Secondary Retinal Ganglion Cell Degeneration. Int J Mol Sci 2023; 24:12109. [PMID: 37569482 PMCID: PMC10418669 DOI: 10.3390/ijms241512109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 07/14/2023] [Accepted: 07/25/2023] [Indexed: 08/13/2023] Open
Abstract
To explore the temporal profile of retinal proteomes specific to primary and secondary retinal ganglion cell (RGC) loss. Unilateral partial optic nerve transection (pONT) was performed on the temporal side of the rat optic nerve. Temporal and nasal retinal samples were collected at 1, 4 and 8 weeks after pONT (n = 4 each) for non-biased profiling with a high-resolution hybrid quadrupole time-of-flight mass spectrometry running on label-free SWATHTM acquisition (SCIEX). An information-dependent acquisition ion library was generated using ProteinPilot 5.0 and OneOmics cloud bioinformatics. Combined proteome analysis detected 2531 proteins with a false discovery rate of <1%. Compared to the nasal retina, 10, 25 and 61 significantly regulated proteins were found in the temporal retina at 1, 4, and 8 weeks, respectively (p < 0.05, FC ≥ 1.4 or ≤0.7). Eight proteins (ALDH1A1, TRY10, GFAP, HBB-B1, ALB, CDC42, SNCG, NEFL) were differentially expressed for at least two time points. The expressions of ALDH1A1 and SNCG at nerve fibers were decreased along with axonal loss. Increased ALDH1A1 localization in the inner nuclear layer suggested stress response. Increased GFAP expression demonstrated regional reactivity of astrocytes and Muller cells. Meta-analysis of gene ontology showed a pronounced difference in endopeptidase and peptidase inhibitor activity. Temporal proteomic profiling demonstrates established and novel protein targets associated with RGC damage.
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Affiliation(s)
- Jacky M. K. Kwong
- Ophthalmology, Stein Eye Institute, University of California Los Angeles, Los Angeles, CA 90095, USA; (J.C.); (J.C.Y.L.); (Y.S.)
| | - Joseph Caprioli
- Ophthalmology, Stein Eye Institute, University of California Los Angeles, Los Angeles, CA 90095, USA; (J.C.); (J.C.Y.L.); (Y.S.)
| | - Joanne C. Y. Lee
- Ophthalmology, Stein Eye Institute, University of California Los Angeles, Los Angeles, CA 90095, USA; (J.C.); (J.C.Y.L.); (Y.S.)
| | - Yifan Song
- Ophthalmology, Stein Eye Institute, University of California Los Angeles, Los Angeles, CA 90095, USA; (J.C.); (J.C.Y.L.); (Y.S.)
| | - Feng-Juan Yu
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
- Research Centre for SHARP Vision (RCSV), The Hong Kong Polytechnic University, Hong Kong, China
| | - Jingfang Bian
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
- Research Centre for SHARP Vision (RCSV), The Hong Kong Polytechnic University, Hong Kong, China
| | - Ying-Hon Sze
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
| | - King-Kit Li
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
| | - Chi-Wai Do
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
- Research Centre for SHARP Vision (RCSV), The Hong Kong Polytechnic University, Hong Kong, China
- Centre for Eye and Vision Research (CEVR), The Hong Kong Polytechnic University, 17W, Hong Kong Science Park, Hong Kong, China
| | - Chi-Ho To
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
- Research Centre for SHARP Vision (RCSV), The Hong Kong Polytechnic University, Hong Kong, China
- Centre for Eye and Vision Research (CEVR), The Hong Kong Polytechnic University, 17W, Hong Kong Science Park, Hong Kong, China
| | - Thomas Chuen Lam
- Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, China; (F.-J.Y.); (J.B.); (Y.-H.S.); (K.-K.L.); (C.-W.D.); (C.-H.T.)
- Research Centre for SHARP Vision (RCSV), The Hong Kong Polytechnic University, Hong Kong, China
- Centre for Eye and Vision Research (CEVR), The Hong Kong Polytechnic University, 17W, Hong Kong Science Park, Hong Kong, China
- Shenzhen Research Institute, The Hong Kong Polytechnic University, Shenzhen 518052, China
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Nadal-Nicolás FM, Galindo-Romero C, Lucas-Ruiz F, Marsh-Amstrong N, Li W, Vidal-Sanz M, Agudo-Barriuso M. Pan-retinal ganglion cell markers in mice, rats, and rhesus macaques. Zool Res 2023; 44:226-248. [PMID: 36594396 PMCID: PMC9841181 DOI: 10.24272/j.issn.2095-8137.2022.308] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Accepted: 12/13/2022] [Indexed: 12/23/2022] Open
Abstract
Univocal identification of retinal ganglion cells (RGCs) is an essential prerequisite for studying their degeneration and neuroprotection. Before the advent of phenotypic markers, RGCs were normally identified using retrograde tracing of retinorecipient areas. This is an invasive technique, and its use is precluded in higher mammals such as monkeys. In the past decade, several RGC markers have been described. Here, we reviewed and analyzed the specificity of nine markers used to identify all or most RGCs, i.e., pan-RGC markers, in rats, mice, and macaques. The best markers in the three species in terms of specificity, proportion of RGCs labeled, and indicators of viability were BRN3A, expressed by vision-forming RGCs, and RBPMS, expressed by vision- and non-vision-forming RGCs. NEUN, often used to identify RGCs, was expressed by non-RGCs in the ganglion cell layer, and therefore was not RGC-specific. γ-SYN, TUJ1, and NF-L labeled the RGC axons, which impaired the detection of their somas in the central retina but would be good for studying RGC morphology. In rats, TUJ1 and NF-L were also expressed by non-RGCs. BM88, ERRβ, and PGP9.5 are rarely used as markers, but they identified most RGCs in the rats and macaques and ERRβ in mice. However, PGP9.5 was also expressed by non-RGCs in rats and macaques and BM88 and ERRβ were not suitable markers of viability.
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Affiliation(s)
- Francisco M Nadal-Nicolás
- Grupo de Oftalmología Experimental, Instituto Murciano de Investigación Biosanitaria Pascual Parrilla (IMIB), Murcia 30120, Spain
- Dpto. Oftalmología, Facultad de Medicina, Universidad de Murcia, Murcia 30120, Spain
- Retinal Neurophysiology Section, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510, USA
| | - Caridad Galindo-Romero
- Grupo de Oftalmología Experimental, Instituto Murciano de Investigación Biosanitaria Pascual Parrilla (IMIB), Murcia 30120, Spain
- Dpto. Oftalmología, Facultad de Medicina, Universidad de Murcia, Murcia 30120, Spain
| | - Fernando Lucas-Ruiz
- Grupo de Oftalmología Experimental, Instituto Murciano de Investigación Biosanitaria Pascual Parrilla (IMIB), Murcia 30120, Spain
- Dpto. Oftalmología, Facultad de Medicina, Universidad de Murcia, Murcia 30120, Spain
| | - Nicholas Marsh-Amstrong
- Department of Ophthalmology and Vision Science, University of California, Davis, CA 95817, USA
| | - Wei Li
- Retinal Neurophysiology Section, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510, USA
| | - Manuel Vidal-Sanz
- Grupo de Oftalmología Experimental, Instituto Murciano de Investigación Biosanitaria Pascual Parrilla (IMIB), Murcia 30120, Spain
- Dpto. Oftalmología, Facultad de Medicina, Universidad de Murcia, Murcia 30120, Spain. E-mail:
| | - Marta Agudo-Barriuso
- Grupo de Oftalmología Experimental, Instituto Murciano de Investigación Biosanitaria Pascual Parrilla (IMIB), Murcia 30120, Spain
- Dpto. Oftalmología, Facultad de Medicina, Universidad de Murcia, Murcia 30120, Spain. E-mail:
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5
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Goleń J, Tyszka J, Godos K, Janse M. A Model of F-actin Organization in Granuloreticulopodia in Foraminifera: Morphogenetic and Evolutionary Implications from Novel Fluorescent and Polarised Light Observations. Protist 2022; 173:125886. [DOI: 10.1016/j.protis.2022.125886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 04/22/2022] [Accepted: 05/08/2022] [Indexed: 11/29/2022]
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6
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Longhena F, Faustini G, Brembati V, Pizzi M, Benfenati F, Bellucci A. An updated reappraisal of synapsins: structure, function and role in neurological and psychiatric disorders. Neurosci Biobehav Rev 2021; 130:33-60. [PMID: 34407457 DOI: 10.1016/j.neubiorev.2021.08.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 07/29/2021] [Accepted: 08/09/2021] [Indexed: 01/02/2023]
Abstract
Synapsins (Syns) are phosphoproteins strongly involved in neuronal development and neurotransmitter release. Three distinct genes SYN1, SYN2 and SYN3, with elevated evolutionary conservation, have been described to encode for Synapsin I, Synapsin II and Synapsin III, respectively. Syns display a series of common features, but also exhibit distinctive localization, expression pattern, post-translational modifications (PTM). These characteristics enable their interaction with other synaptic proteins, membranes and cytoskeletal components, which is essential for the proper execution of their multiple functions in neuronal cells. These include the control of synapse formation and growth, neuron maturation and renewal, as well as synaptic vesicle mobilization, docking, fusion, recycling. Perturbations in the balanced expression of Syns, alterations of their PTM, mutations and polymorphisms of their encoding genes induce severe dysregulations in brain networks functions leading to the onset of psychiatric or neurological disorders. This review presents what we have learned since the discovery of Syn I in 1977, providing the state of the art on Syns structure, function, physiology and involvement in central nervous system disorders.
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Affiliation(s)
- Francesca Longhena
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Gaia Faustini
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Viviana Brembati
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Marina Pizzi
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Fabio Benfenati
- Italian Institute of Technology, Via Morego 30, Genova, Italy; IRCSS Policlinico San Martino Hospital, Largo Rosanna Benzi 10, 16132, Genova, Italy.
| | - Arianna Bellucci
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy; Laboratory for Preventive and Personalized Medicine, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
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7
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Enhanced axonal transport: A novel form of "plasticity" after primate and rodent spinal cord injury. Exp Neurol 2017; 301:59-69. [PMID: 29277625 DOI: 10.1016/j.expneurol.2017.12.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 12/09/2017] [Accepted: 12/21/2017] [Indexed: 11/22/2022]
Abstract
Deficient axonal transport after injury is believed to contribute to the failure of CNS regeneration. To better elucidate neural mechanisms associated with CNS responses to injury, we transected the dominant voluntary motor system, the corticospinal tract (CST), in the dorsolateral T10 spinal cord of rhesus monkeys. Three months later, a 4.5-fold increase in the number of CST axons located in the spared ventral corticospinal tract at both the lesion site and, surprisingly, remotely in the cervical spinal cord was observed. Additional studies of increases in corticospinal axon numbers in rat and primate models demonstrated that increases were transient and attributable to enhanced axonal transport rather than axonal sprouting. Accordingly, increases in axonal transport occur after CNS injury even in the longest projecting pathways of the non-human primate, likely representing an attempted adaptive response to injury as observed in the PNS.
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9
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Ganguly A, Han X, Das U, Wang L, Loi J, Sun J, Gitler D, Caillol G, Leterrier C, Yates JR, Roy S. Hsc70 chaperone activity is required for the cytosolic slow axonal transport of synapsin. J Cell Biol 2017; 216:2059-2074. [PMID: 28559423 PMCID: PMC5496608 DOI: 10.1083/jcb.201604028] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Revised: 08/22/2016] [Accepted: 04/17/2017] [Indexed: 12/19/2022] Open
Abstract
Soluble cytosolic proteins vital to axonal and presynaptic function are synthesized in the neuronal soma and conveyed via slow axonal transport. Our previous studies suggest that the overall slow transport of synapsin is mediated by dynamic assembly/disassembly of cargo complexes followed by short-range vectorial transit (the "dynamic recruitment" model). However, neither the composition of these complexes nor the mechanistic basis for the dynamic behavior is understood. In this study, we first examined putative cargo complexes associated with synapsin using coimmunoprecipitation and multidimensional protein identification technology mass spectrometry (MS). MS data indicate that synapsin is part of a multiprotein complex enriched in chaperones/cochaperones including Hsc70. Axonal synapsin-Hsc70 coclusters are also visualized by two-color superresolution microscopy. Inhibition of Hsc70 ATPase activity blocked the slow transport of synapsin, disrupted axonal synapsin organization, and attenuated Hsc70-synapsin associations, advocating a model where Hsc70 activity dynamically clusters cytosolic proteins into cargo complexes, allowing transport. Collectively, our study offers insight into the molecular organization of cytosolic transport complexes and identifies a novel regulator of slow transport.
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Affiliation(s)
- Archan Ganguly
- Department of Pathology, University of California, San Diego, La Jolla, CA
| | - Xuemei Han
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA
| | - Utpal Das
- Department of Pathology, University of California, San Diego, La Jolla, CA
| | - Lina Wang
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI
| | - Jonathan Loi
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI
| | - Jichao Sun
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI
| | - Daniel Gitler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev and Zlotowski Center for Neuroscience, Beer-Sheva, Israel
| | - Ghislaine Caillol
- Aix Marseille Université, Centre National de la Recherche Scientifique, NICN UMR7259, Marseille, France
| | - Christophe Leterrier
- Aix Marseille Université, Centre National de la Recherche Scientifique, NICN UMR7259, Marseille, France
| | - John R Yates
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA
| | - Subhojit Roy
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI
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Gainer H, House S, Kim DS, Chin H, Pant HC. Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins. Cell Mol Neurobiol 2017; 37:475-486. [PMID: 27207029 DOI: 10.1007/s10571-016-0382-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 05/06/2016] [Indexed: 12/16/2022]
Abstract
When isolated squid giant axons are incubated in radioactive amino acids, abundant newly synthesized proteins are found in the axoplasm. These proteins are translated in the adaxonal Schwann cells and subsequently transferred into the giant axon. The question as to whether any de novo protein synthesis occurs in the giant axon itself is difficult to resolve because the small contribution of the proteins possibly synthesized intra-axonally is not easily distinguished from the large amounts of the proteins being supplied from the Schwann cells. In this paper, we reexamine this issue by studying the synthesis of endogenous neurofilament (NF) proteins in the axon. Our laboratory previously showed that NF mRNA and protein are present in the squid giant axon, but not in the surrounding adaxonal glia. Therefore, if the isolated squid axon could be shown to contain newly synthesized NF protein de novo, it could not arise from the adaxonal glia. The results of experiments in this paper show that abundant 3H-labeled NF protein is synthesized in the squid giant fiber lobe containing the giant axon's neuronal cell bodies, but despite the presence of NF mRNA in the giant axon no labeled NF protein is detected in the giant axon. This lends support to the glia-axon protein transfer hypothesis which posits that the squid giant axon obtains newly synthesized protein by Schwann cell transfer and not through intra-axonal protein synthesis, and further suggests that the NF mRNA in the axon is in a translationally repressed state.
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Affiliation(s)
- Harold Gainer
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA.
| | - Shirley House
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA
| | - Dong Sun Kim
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA
- Department of Anatomy, College of Medicine, Kyungbuk National University, Daegu, South Korea
| | - Hemin Chin
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA
- Division of Extramural Research, National Eye Institute, NIH, Bethesda, MD, 20892, USA
| | - Harish C Pant
- Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA
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11
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Problems and Solutions in Click Chemistry Applied to Drug Probes. Sci Rep 2016; 6:35579. [PMID: 27782133 PMCID: PMC5080546 DOI: 10.1038/srep35579] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 09/30/2016] [Indexed: 01/24/2023] Open
Abstract
Small-molecule fluorescent probes have been widely used in target identification, but this method has many disadvantages. For example, the identified proteins are usually complex, and additional biochemical studies are needed to distinguish real targets from interference results. To address this problem, we propose a series of strategies for improving the efficiency of target identification. First, pretreatment with a lower concentration of hydrogen peroxide can shield against thiol interference. Second, the use of benzophenone as a photo-affinity group is not appropriate, and diazirines are preferred. Third, if cytoskeleton proteins or stress proteins are captured, the interference must be carefully eliminated. The specificity of target identification can be improved by optimizing these three strategies. In this paper, we discuss the problems associated with the use of the click reaction in living cells and provide important complementary techniques for photo-affinity probes based on the click chemistry reaction.
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López-Leal R, Alvarez J, Court FA. Origin of axonal proteins: Is the axon-schwann cell unit a functional syncytium? Cytoskeleton (Hoboken) 2016; 73:629-639. [DOI: 10.1002/cm.21319] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 07/28/2016] [Accepted: 08/02/2016] [Indexed: 12/31/2022]
Affiliation(s)
- Rodrigo López-Leal
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Geroscience Center for Brain Health and Metabolism; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
| | - Jaime Alvarez
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
| | - Felipe A. Court
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Geroscience Center for Brain Health and Metabolism; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
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Penazzi L, Bakota L, Brandt R. Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 321:89-169. [PMID: 26811287 DOI: 10.1016/bs.ircmb.2015.09.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.
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Affiliation(s)
- Lorène Penazzi
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
| | - Lidia Bakota
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
| | - Roland Brandt
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
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15
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Chetta J, Love JM, Bober BG, Shah SB. Bidirectional actin transport is influenced by microtubule and actin stability. Cell Mol Life Sci 2015; 72:4205-20. [PMID: 26043972 PMCID: PMC11113749 DOI: 10.1007/s00018-015-1933-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 05/14/2015] [Accepted: 05/19/2015] [Indexed: 12/16/2022]
Abstract
Local and long-distance transport of cytoskeletal proteins is vital to neuronal maintenance and growth. Though recent progress has provided insight into the movement of microtubules and neurofilaments, mechanisms underlying the movement of actin remain elusive, in large part due to rapid transitions between its filament states and its diverse cellular localization and function. In this work, we integrated live imaging of rat sensory neurons, image processing, multiple regression analysis, and mathematical modeling to perform the first quantitative, high-resolution investigation of GFP-actin identity and movement in individual axons. Our data revealed that filamentous actin densities arise along the length of the axon and move short but significant distances bidirectionally, with a net anterograde bias. We directly tested the role of actin and microtubules in this movement. We also confirmed a role for actin densities in extension of axonal filopodia, and demonstrated intermittent correlation of actin and mitochondrial movement. Our results support a novel mechanism underlying slow component axonal transport, in which the stability of both microtubule and actin cytoskeletal components influence the mobility of filamentous actin.
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Affiliation(s)
- Joshua Chetta
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - James M Love
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - Brian G Bober
- Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA
| | - Sameer B Shah
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.
- Departments of Orthopaedic Surgery and Bioengineering, University of California, San Diego, 9500 Gilman Drive, MC 0863, La Jolla, CA, 92093, USA.
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16
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Mussel M, Zeevy K, Diamant H, Nevo U. Drag of the cytosol as a transport mechanism in neurons. Biophys J 2015; 106:2710-9. [PMID: 24940788 DOI: 10.1016/j.bpj.2014.04.037] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 03/26/2014] [Accepted: 04/28/2014] [Indexed: 01/15/2023] Open
Abstract
Axonal transport is typically divided into two components, which can be distinguished by their mean velocity. The fast component includes steady trafficking of different organelles and vesicles actively transported by motor proteins. The slow component comprises nonmembranous materials that undergo infrequent bidirectional motion. The underlying mechanism of slow axonal transport has been under debate during the past three decades. We propose a simple displacement mechanism that may be central for the distribution of molecules not carried by vesicles. It relies on the cytoplasmic drag induced by organelle movement and readily accounts for key experimental observations pertaining to slow-component transport. The induced cytoplasmic drag is predicted to depend mainly on the distribution of microtubules in the axon and the organelle transport rate.
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Affiliation(s)
- Matan Mussel
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Keren Zeevy
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Haim Diamant
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
| | - Uri Nevo
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel; Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel.
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17
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Abstract
The advent of photoactivatable tools has revolutionized imaging of dynamic cellular processes. One such application is to visualize axonal transport-an intricate and dynamic process by which proteins and other macromolecules are conveyed from their sites of synthesis in the cell bodies to their destinations within axons and synapses. High-quality dynamic imaging of axonal transport using photoactivatable vectors can now be routinely performed using epifluorescence microscopes and CCD cameras that are standard in most laboratories, yet this is largely underutilized. Here we describe detailed protocols for imaging cargoes moving in fast and slow axonal transport in axons of cultured hippocampal neurons.
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Affiliation(s)
- Archan Ganguly
- Department of Pathology, University of California, San Diego, 9500 Gilman Drive, BSB 1029, MC0612, La Jolla, CA, 92093, USA,
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18
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Abstract
Although it is known that cytosolic/soluble proteins synthesized in cell bodies are transported at much lower overall velocities than vesicles in fast axonal transport, the fundamental basis for this slow movement is unknown. Recently, we found that cytosolic proteins in axons of mouse cultured neurons are conveyed in a manner that superficially resembles diffusion, but with a slow anterograde bias that is energy- and motor-dependent (Scott et al., 2011). Here we show that slow axonal transport of synapsin, a prototypical member of this rate class, is dependent upon fast vesicle transport. Despite the distinct overall dynamics of slow and fast transport, experimentally induced and intrinsic variations in vesicle transport have analogous effects on slow transport of synapsin as well. Dynamic cotransport of vesicles and synapsin particles is also seen in axons, consistent with a model where higher-order assemblies of synapsin are conveyed by transient and probabilistic associations with vesicles moving in fast axonal transport. We posit that such dynamic associations generate the slow overall anterogradely biased flow of the population ("dynamic-recruitment model"). Our studies uncover the underlying kinetic basis for a classic cytosolic/soluble protein moving in slow axonal transport and reveal previously unknown links between slow and fast transport, offering a clearer conceptual picture of this curious phenomenon.
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19
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Kuznetsov IA, Kuznetsov AV. Modeling anterograde and retrograde transport of short mobile microtubules from the site of axonal branch formation. J Biol Phys 2013; 40:41-53. [PMID: 24271236 DOI: 10.1007/s10867-013-9334-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 10/14/2013] [Indexed: 10/26/2022] Open
Abstract
This theoretical research is motivated by a recent model of microtubule (MT) transport put forward by Baas and Mozgova (Cytoskeleton 69:416-425, 2012). According to their model, in an axon all plus-end-distal mobile MTs move anterogradely while all minus-end-distal mobile MTs move retrogradely. Retrograde MT transport thus represents a mechanism by which minus-end-distal MTs are removed from the axon. We suggested equations that implement Baas and Mozgova's model. We employed these equations to simulate transport of short mobile MTs from a region (such as the site of axonal branch formation) where MT severing activity results in generation of a large number of short MTs of both orientations. We obtained the exact and approximate transient solutions of these equations utilizing the Laplace transform technique. We applied the obtained solutions to calculate the average rates of anterograde and retrograde transport of short MTs.
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Affiliation(s)
- I A Kuznetsov
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, 21218-2694, USA,
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20
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Abstract
Axonal transport is the lifeline of axons and synapses. After synthesis in neuronal cell bodies, proteins are conveyed into axons in two distinct rate classes-fast and slow axonal transport. Whereas fast transport delivers vesicular cargoes, slow transport carries cytoskeletal and cytosolic (or soluble) proteins that have critical roles in neuronal structure and function. Although significant progress has been made in dissecting the molecular mechanisms of fast vesicle transport, mechanisms of slow axonal transport are less clear. Why is this so? Historically, conceptual advances in the axonal transport field have paralleled innovations in imaging the movement, and slow-transport cargoes are not as readily seen as motile vesicles. However, new ways of visualizing slow transport have reenergized the field, leading to fundamental insights that have changed our views on axonal transport, motor regulation, and intracellular trafficking in general. This review first summarizes classic studies that characterized axonal transport, and then discusses recent technical and conceptual advances in slow axonal transport that have provided insights into some long-standing mysteries.
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Affiliation(s)
- Subhojit Roy
- 1Department of Pathology, University of California, San Diego, La Jolla, CA, USA
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21
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Abbott CJ, Choe TE, Lusardi TA, Burgoyne CF, Wang L, Fortune B. Imaging axonal transport in the rat visual pathway. BIOMEDICAL OPTICS EXPRESS 2013; 4:364-386. [PMID: 23412846 PMCID: PMC3567722 DOI: 10.1364/boe.4.000364] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Revised: 01/10/2013] [Accepted: 01/28/2013] [Indexed: 06/01/2023]
Abstract
A technique was developed for assaying axonal transport in retinal ganglion cells using 2 µl injections of 1% cholera toxin b-subunit conjugated to AlexaFluor488 (CTB). In vivo retinal and post-mortem brain imaging by confocal scanning laser ophthalmoscopy and post-mortem microscopy were performed. The transport of CTB was sensitive to colchicine, which disrupts axonal microtubules. The bulk rates of transport were determined to be approximately 80-90 mm/day (anterograde) and 160 mm/day (retrograde). Results demonstrate that axonal transport of CTB can be monitored in vivo in the rodent anterior visual pathway, is dependent on intact microtubules, and occurs by active transport mechanisms.
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Affiliation(s)
- Carla J. Abbott
- Discoveries in Sight Research Laboratories, Devers Eye Institute, and
Legacy Research Institute, Legacy Health, Portland, OR 97232, USA
| | - Tiffany E. Choe
- Discoveries in Sight Research Laboratories, Devers Eye Institute, and
Legacy Research Institute, Legacy Health, Portland, OR 97232, USA
| | - Theresa A. Lusardi
- R.S. Dow Neurobiology Laboratories, Legacy Research Institute, Legacy
Health, Portland, OR 97232, USA
| | - Claude F. Burgoyne
- Discoveries in Sight Research Laboratories, Devers Eye Institute, and
Legacy Research Institute, Legacy Health, Portland, OR 97232, USA
| | - Lin Wang
- Discoveries in Sight Research Laboratories, Devers Eye Institute, and
Legacy Research Institute, Legacy Health, Portland, OR 97232, USA
| | - Brad Fortune
- Discoveries in Sight Research Laboratories, Devers Eye Institute, and
Legacy Research Institute, Legacy Health, Portland, OR 97232, USA
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23
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Abstract
A peripheral nerve trunk is composed of nerve fascicles supported in a fibrous collagenous sheath and defined by concentric layers of cells (the perineurium) that separate the contents (the endoneurium) from its fibrous collagen support (the epineurium). In the endoneurium are myelinated and unmyelinated fibers that are axons combined with their supporting Schwann cells to provide physical and electrical connections with end-organs such as muscle fibers and sensory endings. Axons are tubular neuronal extensions with a cytoskeleton of neurotubules and tubulin along which organelles and proteins can travel between the neuronal cell body and the axon terminal. During development some axons enlarge and are covered by a chain of Schwann cells each associated with just one axon. As the axons grow in diameter, the Schwann cells wrap round them to produce a myelin sheath. This consists of many layers of compacted Schwann cell membrane plus some additional proteins. Adjacent myelin segments connect at highly specialized structures, the nodes of Ranvier. Myelin insulates the axon so that the nerve impulse can jump from one node to the next. The region adjacent to the node, the paranodal segment, is the site of myelin terminations on the axolemma. There are connections here between the Schwann cell and the axon via a complex chain of proteins. The Schwann cell cytoplasm in the adjacent segment, the juxtaparanode, contains most of the Schwann cell mitochondria. In addition to the node, continuity of myelin lamellae is broken at intervals along the internode by helical regions of decompaction known as Schmidt-Lanterman incisures; these are seen as paler conical segments in suitably stained microscopical preparations and provide a pathway between the adaxonal and abaxonal cytoplasm. Smaller axons without a myelin sheath conduct very much more slowly and have a more complex relationship with their supporting Schwann cells that has important implications for repair.
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Affiliation(s)
- Rosalind King
- Department of Clinical Neurosciences, Institute of Neurology, University College London, Royal Free Campus, London, UK.
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24
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Brown A, Jung P. A critical reevaluation of the stationary axonal cytoskeleton hypothesis. Cytoskeleton (Hoboken) 2012; 70:1-11. [PMID: 23027591 DOI: 10.1002/cm.21083] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 09/13/2012] [Accepted: 09/24/2012] [Indexed: 01/05/2023]
Abstract
Neurofilaments are transported along axons in a rapid intermittent and bidirectional manner but there is a long-standing controversy about whether this applies to all axonal neurofilaments. Some have proposed that only a small proportion of axonal neurofilaments are mobile and that most are deposited into a persistently stationary and extensively cross-linked cytoskeleton that remains fixed in place for many months without movement, turning over very slowly. In contrast, others have proposed that this hypothesis is based on a misinterpretation of the experimental data and that, in fact, all axonal neurofilaments move. These contrary perspectives have distinct implications for our understanding of how neurofilaments are organized and reorganized in axons both in health and disease. Here, we discuss the history and substance of this controversy. We show that the published data on the kinetics and distribution of neurofilaments along axons favor a simple "stop and go" transport model in which axons contain a single population of neurofilaments that all move in a stochastic, bidirectional and intermittent manner. Based on these considerations, we propose a dynamic view of the neuronal cytoskeleton in which all neurofilaments cycle repeatedly between moving and pausing states throughout their journey along the axon. The filaments move infrequently, but the average pause duration is on the order of hours rather than weeks or months. Against this fluid backdrop, the action of molecular motors on neurofilaments can have dramatic effects on neurofilament organization that would not be possible if the neurofilaments were extensively cross-linked into a truly stationary network.
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Affiliation(s)
- Anthony Brown
- Department of Neuroscience, The Ohio State University, Columbus, OH 43210, USA.
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25
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Fischer I, Romano-Clarke G. Association of microtubule-associated protein (MAP1B) with growing axons in cultured hippocampal neurons. Mol Cell Neurosci 2012; 2:39-51. [PMID: 19912782 DOI: 10.1016/1044-7431(91)90038-p] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/1991] [Indexed: 11/19/2022] Open
Abstract
Microtubule-associated protein 1B (MAP1B) is a major constituent of the neuronal cytoskeleton early in development. This protein is present in embryonic brain and is composed of two isoforms that are the result of differential phosphorylation. We examined the distribution of MAP1B during the differentiation of cultured hippocampal neurons and compared it to that of MAP2 and tubulin. We demonstrated by immunofluorescent doublestaining that MAP1B and MAP2 are colocalized in cell bodies and the minor processes of hippocampal neurons during the early stages of development, before the establishment of neuronal polarity. Later, when neurons acquire axonal and dendritic characteristics, MAP1B is sorted into growing axons, including the growth cone, whereas MAP2 is restricted to dendrites and cell bodies. Unlike tubulin, the localization of MAP1B in growing axons is not uniform. Rather, the protein is found concentrated in the distal portion. During later stages of development, the neurons extend a network of fasciculating axonal and dendritic neurites in which the segregation of MAP1B and MAP2 is maintained. However, the staining of MAP1B in mature neuronal cultures decreases in a pattern that resembles the decline of this protein during brain development. These results support the association of MAP1B with growing axons and its correct developmental regulation in the hippocampal culture system.
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Affiliation(s)
- I Fischer
- Department of Biochemistry, E. K. Shriver Center, Waltham, Massachusetts 02254, USA; Department of Neurology (Neuroscience), Harvard Medical School, Boston, Massachusetts 02115, USA
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26
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Mongin AA, Dohare P, Jourd'heuil D. Selective vulnerability of synaptic signaling and metabolism to nitrosative stress. Antioxid Redox Signal 2012; 17:992-1012. [PMID: 22339371 PMCID: PMC3411350 DOI: 10.1089/ars.2012.4559] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
SIGNIFICANCE Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells. RECENT ADVANCES Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability. CRITICAL ISSUES The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols. FUTURE DIRECTIONS We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.
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Affiliation(s)
- Alexander A Mongin
- Center for Neuropharmacology and Neuroscience, Albany Medical College, New York 12208, USA.
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27
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Gu Y, Sun W, Wang G, Jeftinija K, Jeftinija S, Fang N. Rotational dynamics of cargos at pauses during axonal transport. Nat Commun 2012; 3:1030. [DOI: 10.1038/ncomms2037] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Accepted: 07/31/2012] [Indexed: 01/13/2023] Open
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28
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Sadananda A, Ray K. Neurogenetics of slow axonal transport: from cells to animals. J Neurogenet 2012; 26:291-7. [PMID: 22834647 DOI: 10.3109/01677063.2012.699564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Slow axonal transport is a multivariate phenomenon implicated in several neurodegenerative disorders. Recent reports have unraveled the molecular basis of the transport of certain slow component proteins, such as the neurofilament subunits, tubulin, and certain soluble enzymes such as Ca(2+)/calmodulin-dependent protein kinase IIa (CaM kinase IIa), etc., in tissue cultured neurons. In addition, genetic analyses also implicate microtubule-dependent motors and other housekeeping proteins in this process. However, the biological relevance of this phenomenon is not so well understood. Here, the authors have discussed the possibility of adopting neurogenetic analyses in multiple model organisms to correlate molecular level measurements of the slow transport phenomenon to animal behavior, thus facilitating the investigation of its biological efficacy.
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Axonal transport of neurofilaments: a single population of intermittently moving polymers. J Neurosci 2012; 32:746-58. [PMID: 22238110 DOI: 10.1523/jneurosci.4926-11.2012] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Studies on mouse optic nerve have led to the controversial proposal that only a small proportion of neurofilaments are transported in axons and that the majority are deposited into a persistently stationary and extensively cross-linked cytoskeletal network that remains fixed in place for months without movement. We have used computational modeling to address this issue, taking advantage of the wealth of published kinetic and morphometric data available for neurofilaments in the mouse visual system. We show that the transport kinetics and distribution of neurofilaments in mouse optic nerve can all be explained fully by a "stop-and-go" model of neurofilament transport, in which axons contain a single population of neurofilaments that all move stochastically in a rapid, intermittent, and bidirectional manner. Importantly, we find that the transport kinetics are not consistent with deposition of neurofilaments into a persistently stationary phase, and that deposition models cannot account for the observed distribution of neurofilaments along mouse optic nerve axons. Finally, we show that the apparent existence of a stationary neurofilament network in mouse optic nerve is most likely an experimental artifact due to contamination of the neurofilament transport kinetics with cytosolic proteins that move at faster rates. Thus, there is no evidence for the deposition of axonally transported neurofilaments into a persistently stationary neurofilament network in optic nerve axons. We conclude that all of the neurofilaments move and that they do so with a single broad and continuous distribution of average rates that is dictated by their intermittent and stochastic motile behavior.
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30
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Baas PW, Mozgova OI. A novel role for retrograde transport of microtubules in the axon. Cytoskeleton (Hoboken) 2012; 69:416-25. [PMID: 22328357 DOI: 10.1002/cm.21013] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 01/26/2012] [Accepted: 01/27/2012] [Indexed: 01/14/2023]
Abstract
Short microtubules move within the axon in both directions. In the past, it had been assumed that all of the short moving microtubules are oriented with their plus-ends distal to the cell body, regardless of their direction of movement. The anterogradely moving microtubules were posited to play critical roles in the establishment, expansion, and maintenance of the axonal microtubule array. There was no known function for the retrogradely moving microtubules. In considering the mechanism of their transport, we had assumed that all of the short microtubules have a plus-end-distal polarity orientation, as is characteristic of the long microtubules that dominate the axon. Here we discuss an alternative hypothesis, namely that the short microtubules moving retrogradely have the opposite polarity orientation of those moving anterogradely. Those that move anterogradely have their plus-ends distal to the cell body while those that move retrogradely have their minus ends distal to the cell body. In this view, retrograde transport is a means for clearing the axon of incorrectly oriented microtubules. This new model, if correct, has profound implications for the manner by which healthy axons preserve their characteristic pattern of microtubule polarity orientation. We speculate that pathological flaws in this mechanism may be a critical factor in the degeneration of axons during disease and injury, as well as in neuropathy caused by microtubule-active drugs.
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Affiliation(s)
- Peter W Baas
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
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31
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Hares K, Kemp K, Gray E, Scolding N, Wilkins A. Neurofilament dot blot assays: Novel means of assessing axon viability in culture. J Neurosci Methods 2011; 198:195-203. [DOI: 10.1016/j.jneumeth.2011.03.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 03/23/2011] [Accepted: 03/28/2011] [Indexed: 10/18/2022]
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32
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Dahlstrom AB. Fast intra-axonal transport: Beginning, development and post-genome advances. Prog Neurobiol 2010; 90:119-45. [DOI: 10.1016/j.pneurobio.2009.11.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 11/23/2009] [Accepted: 11/23/2009] [Indexed: 01/02/2023]
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Abstract
Axons are occupied by dense arrays of cytoskeletal elements called microtubules, which are critical for generating and maintaining the architecture of the axon, and for acting as railways for the transport of organelles in both directions within the axon. Microtubules are organized and regulated by molecules that affect their assembly and disassembly, their stabilization, their association with other cytoskeletal elements, and their alignment and bundling with one another. Recent studies have accentuated the role of molecular motor proteins and microtubule-severing proteins in the establishment and maintenance of the axonal microtubule array. The growing body of knowledge on the proteins and mechanisms that regulate axonal microtubules has fostered a better understanding of how many debilitating diseases cause axons to degenerate. The purpose of this chapter is to provide an update on current knowledge of axonal microtubules and the proteins that regulate them, and to reflect on cutting-edge findings linking these proteins and mechanisms to diseases that afflict the human population.
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35
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Perrot R, Berges R, Bocquet A, Eyer J. Review of the Multiple Aspects of Neurofilament Functions, and their Possible Contribution to Neurodegeneration. Mol Neurobiol 2008; 38:27-65. [DOI: 10.1007/s12035-008-8033-0] [Citation(s) in RCA: 205] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Accepted: 06/14/2008] [Indexed: 10/21/2022]
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Abstract
Slow component-b (SCb) translocates approximately 200 diverse proteins from the cell body to the axon and axon tip at average rates of approximately 2-8 mm/d. Several studies suggest that SCb proteins are cotransported as one or more macromolecular complexes, but the basis for this cotransport is unknown. The identification of actin and myosin in SCb led to the proposal that actin filaments function as a scaffold for the binding of other SCb proteins and that transport of these complexes is powered by myosin: the "microfilament-complex" model. Later, several SCb proteins were also found to bind F-actin, supporting the idea, but despite this, the model has never been directly tested. Here, we test this model by disrupting the cytoskeleton in a live-cell model system wherein we directly visualize transport of SCb cargoes. We focused on three SCb proteins that we previously showed were cotransported in our system: alpha-synuclein, synapsin-I, and glyceraldehyde-3-phosphate dehydrogenase. Disruption of actin filaments with latrunculin had no effect on the velocity or frequency of transport of these three proteins. Furthermore, cotransport of these three SCb proteins continued in actin-depleted axons. We conclude that actin filaments do not function as a scaffold to organize and transport these and possibly other SCb proteins. In contrast, depletion of microtubules led to a dramatic inhibition of vectorial transport of SCb cargoes. These findings do not support the microfilament-complex model, but instead indicate that the transport of protein complexes in SCb is powered by microtubule motors.
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37
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Giuditta A, Tai Chun J, Eyman M, Cefaliello C, Bruno AP, Crispino M. Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit. Physiol Rev 2008; 88:515-55. [DOI: 10.1152/physrev.00051.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Neurons have complex and often extensively elongated processes. This unique cell morphology raises the problem of how remote neuronal territories are replenished with proteins. For a long time, axonal and presynaptic proteins were thought to be exclusively synthesized in the cell body, which delivered them to peripheral sites by axoplasmic transport. Despite this early belief, protein has been shown to be synthesized in axons and nerve terminals, substantially alleviating the trophic burden of the perikaryon. This observation raised the question of the cellular origin of the peripheral RNAs involved in protein synthesis. The synthesis of these RNAs was initially attributed to the neuron soma almost by default. However, experimental data and theoretical considerations support the alternative view that axonal and presynaptic RNAs are also transcribed in the flanking glial cells and transferred to the axon domain of mature neurons. Altogether, these data suggest that axons and nerve terminals are served by a distinct gene expression system largely independent of the neuron cell body. Such a local system would allow the neuron periphery to respond promptly to environmental stimuli. This view has the theoretical merit of extending to axons and nerve terminals the marginalized concept of a glial supply of RNA (and protein) to the neuron cell body. Most long-term plastic changes requiring de novo gene expression occur in these domains, notably in presynaptic endings, despite their intrinsic lack of transcriptional capacity. This review enlightens novel perspectives on the biology and pathobiology of the neuron by critically reviewing these issues.
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Roy S, Winton MJ, Black MM, Trojanowski JQ, Lee VMY. Rapid and intermittent cotransport of slow component-b proteins. J Neurosci 2007; 27:3131-8. [PMID: 17376974 PMCID: PMC6672457 DOI: 10.1523/jneurosci.4999-06.2007] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
After synthesis in neuronal perikarya, proteins destined for synapses and other distant axonal sites are transported in three major groups that differ in average velocity and protein composition: fast component (FC), slow component-a (SCa), and slow component-b (SCb). The FC transports mainly vesicular cargoes at average rates of approximately 200-400 mm/d. SCa transports microtubules and neurofilaments at average rates of approximately 0.2-1 mm/d, whereas SCb translocates approximately 200 diverse proteins critical for axonal growth, regeneration, and synaptic function at average rates of approximately 2-8 mm/d. Several neurodegenerative diseases are characterized by abnormalities in one or more SCb proteins, but little is known about mechanisms underlying SCb compared with FC and SCa. Here, we use live-cell imaging to visualize and quantify the axonal transport of three SCb proteins, alpha-synuclein, synapsin-I, and glyceraldehyde-3-phosphate dehydrogenase in cultured hippocampal neurons, and directly compare their transport to synaptophysin, a prototypical FC protein. All three SCb proteins move rapidly but infrequently with pauses during transit, unlike synaptophysin, which moves much more frequently and persistently. By simultaneously visualizing the transport of proteins at high temporal and spatial resolution, we show that the dynamics of alpha-synuclein transport are distinct from those of synaptophysin but similar to other SCb proteins. Our observations of the cotransport of multiple SCb proteins in single axons suggest that they move as multiprotein complexes. These studies offer novel mechanistic insights into SCb and provide tools for further investigating its role in disease processes.
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Affiliation(s)
- Subhojit Roy
- Center for Neurodegenerative Disease Research
- Department of Pathology and Laboratory Medicine, and
| | | | - Mark M. Black
- Department of Anatomy and Cell Biology, Temple University Hospital, Philadelphia, Pennsylvania 19130
| | - John Q. Trojanowski
- Center for Neurodegenerative Disease Research
- Department of Pathology and Laboratory Medicine, and
- Institute on Aging, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, and
| | - Virginia M.-Y. Lee
- Center for Neurodegenerative Disease Research
- Department of Pathology and Laboratory Medicine, and
- Institute on Aging, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, and
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39
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Yuan A, Nixon RA, Rao MV. Deleting the phosphorylated tail domain of the neurofilament heavy subunit does not alter neurofilament transport rate in vivo. Neurosci Lett 2005; 393:264-8. [PMID: 16266786 DOI: 10.1016/j.neulet.2005.10.029] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2005] [Revised: 09/07/2005] [Accepted: 10/01/2005] [Indexed: 11/25/2022]
Abstract
Phosphorylation of the carboxyl tail domains of the neurofilament heavy (NF-H) and middle molecular weight (NF-M) subunits has been proposed to regulate the axonal transport of neurofilaments. To test this hypothesis, we recently constructed mice lacking the extensively phosphorylated NF-H tail domain (NF-HtailDelta) and showed that the transport rate of neurofilaments in optic axons is unaltered in the absence of this domain [M.V. Rao, M.L. Garcia, Y. Miyazaki, T. Gotow, A. Yuan, S. Mattina, C.M. Ward, N.A. Calcutt, Y. Uchiyama, R.A. Nixon, D.W. Cleveland, Gene replacement in mice reveals that the heavily phosphorylated tail of neurofilament heavy subunit does not affect axonal caliber or the transit of cargoes in slow axonal transport, J. Cell Biol. 158 (2002) 681-693]. However, Shea et al. proposed that deletion of NF-H carboxyl-terminal region accelerates the transport of a subpopulation of neurofilaments based on minor differences between tail-deleted and control mice in our axonal transport analysis. Here, we present additional evidence that neurofilament transport rate is unchanged after deleting the phosphorylated NF-H tail domain, establishing unequivocally that the NF-H tail domain alone does not regulate the rate of neurofilament transport in optic axons in vivo. Possible roles for tail domains as cross-bridges between a neurofilament and its neighbors or other cytoskeletal elements is discussed.
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Affiliation(s)
- Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, New York University School of Medicine, 140 Old Orangeburg Road, Orangeburg, NY 10962, USA
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40
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Abstract
Retinal ganglion cells are the output cells of the retina whose axons are under considerable metabolic stress in both health and disease states. They are highly polarised to ensure that mitochondria and enzymes involved in the generation of ATP are strategically concentrated to meet the local energy demands of the cell. In passing from the eye to the brain, axons are protected and supported by glial tissues and the blood supply of the optic nerve head is regulated to maintain the supply of oxygen and nutrients to the axons. In spite of this, the optic nerve head remains the point at which retinal ganglion cell axons are most vulnerable to the effects of increased intraocular pressure or ischaemia. Considerable work has been undertaken in this area to advance our understanding on the pathophysiology of axon damage and to develop new strategies for the prevention of retinal ganglion cell death.
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Affiliation(s)
- J E Morgan
- Department of Ophthalmology, University Hospital of Wales, Heath Park, Cardiff, UK.
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41
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Reid SNM, Farber DB. Glial transcytosis of a photoreceptor-secreted signaling protein, retinoschisin. Glia 2005; 49:397-406. [PMID: 15538749 DOI: 10.1002/glia.20131] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In vitro studies have clearly shown that signaling/guidance proteins can diffuse to their targets. However, it is unclear whether they can travel by diffusion in vivo, or if they are distributed in the tissue by an active mechanism. Retinoschisin, a signaling molecule related to neuropilins, is synthesized and secreted by photoreceptor cells in the outer retina; then it interacts with inner retinal cells contributing to synaptic organization and optic nerve fiber integrity. We developed an assay to examine how retinoschisin, which is secreted a distance away, reaches its inner retinal targets. We found that retinoschisin is preferentially taken up and carried into the inner retina from the retinal outer border (the photoreceptor side) by Müller cells (the main glial cells of the vertebrate retina). This transcytosis is disrupted by DL-alpha-aminoadipic acid, a Müller cell/glia-specific toxin. Our results suggest that glial uptake/transcytosis can provide an effective and precise alternative for distributing signaling molecules in the nervous system.
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Affiliation(s)
- Silvia N M Reid
- Jules Stein Eye Institute, UCLA School of Medicine Center for the Health Sciences, 100 Stein Plaza, Los Angeles, CA 90095-7008, USA.
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42
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He Y, Francis F, Myers KA, Yu W, Black MM, Baas PW. Role of cytoplasmic dynein in the axonal transport of microtubules and neurofilaments. ACTA ACUST UNITED AC 2005; 168:697-703. [PMID: 15728192 PMCID: PMC2171826 DOI: 10.1083/jcb.200407191] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Recent studies have shown that the transport of microtubules (MTs) and neurofilaments (NFs) within the axon is rapid, infrequent, asynchronous, and bidirectional. Here, we used RNA interference to investigate the role of cytoplasmic dynein in powering these transport events. To reveal transport of MTs and NFs, we expressed EGFP-tagged tubulin or NF proteins in cultured rat sympathetic neurons and performed live-cell imaging of the fluorescent cytoskeletal elements in photobleached regions of the axon. The occurrence of anterograde MT and retrograde NF movements was significantly diminished in neurons that had been depleted of dynein heavy chain, whereas the occurrence of retrograde MT and anterograde NF movements was unaffected. These results support a cargo model for NF transport and a sliding filament model for MT transport.
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Affiliation(s)
- Yan He
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA
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43
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Verma P, Chierzi S, Codd AM, Campbell DS, Meyer RL, Holt CE, Fawcett JW. Axonal protein synthesis and degradation are necessary for efficient growth cone regeneration. J Neurosci 2005; 25:331-42. [PMID: 15647476 PMCID: PMC3687202 DOI: 10.1523/jneurosci.3073-04.2005] [Citation(s) in RCA: 309] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2004] [Revised: 11/04/2004] [Accepted: 11/12/2004] [Indexed: 11/21/2022] Open
Abstract
Axonal regeneration can occur within hours of injury, the first step being the formation of a new growth cone. For sensory and retinal axons, regenerative ability in vivo correlates with the potential to form a new growth cone after axotomy in vitro. We show that this ability to regenerate a new growth cone depends on local protein synthesis and degradation within the axon. Axotomy in vitro leads to a fourfold to sixfold increase in 3H-leucine incorporation in both neurones and axons, starting within 10 min and peaking 1 h after axotomy. Application of protein synthesis inhibitors (cycloheximide and anisomycin) to cut axons, including axons whose cell bodies were removed, or proteasome inhibitors (lactacystin and N-acetyl-Nor-Leu-Leu-Al) all result in a reduction in the proportion of transected axons able to reform growth cones. Similar inhibition of growth cone formation was observed on addition of target of rapamycin (TOR), p38 MAPK (mitogen-activated protein kinase), and caspase-3 inhibitors. Comparing retinal and sensory axons of different developmental stages, levels of ribosomal protein P0 and phosphorylated translation initiation factor are high in sensory axons, lower in embryonic axons, and absent in adult retinal axons. Conditioning lesions, which increase the regenerative ability of sensory axons, lead to increases in intra-axonal protein synthetic and degradative machinery both in vitro and in vivo. Collectively, these findings suggest that local protein synthesis and degradation, controlled by various TOR-, p38 MAPK-, and caspase-dependent pathways, underlie growth cone initiation after axotomy.
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Affiliation(s)
- Poonam Verma
- Cambridge University Centre for Brain Repair, Cambridge CB2 2PY, United Kingdom
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44
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Ma Y, Shakiryanova D, Vardya I, Popov SV. Quantitative Analysis of Microtubule Transport in Growing Nerve Processes. Curr Biol 2004; 14:725-30. [PMID: 15084289 DOI: 10.1016/j.cub.2004.03.061] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2003] [Revised: 01/19/2004] [Accepted: 03/02/2004] [Indexed: 11/24/2022]
Abstract
In neurons, tubulin is synthesized primarily in the cell body, whereas the molecular machinery for neurite extension and elaboration of microtubule (MT) array is localized to the growth cone region. This unique functional and biochemical compartmentalization of neuronal cells requires transport mechanisms for the delivery of newly synthesized tubulin and other cytoplasmic components from the cell body to the growing axon. According to the polymer transport model, tubulin is transported along the axon as a polymer. Because the majority of axonal MTs are stationary at any given moment, it has been assumed that only a small fraction of MTs translocates along the axon by saltatory movement reminiscent of the fast axonal transport. Such intermittent "stop and go" MT transport has been difficult to detect or to exclude by using direct video microscopy methods. In this study, we measured the translocation of MT plus ends in the axonal shaft by expressing GFP-EB1 in Xenopus embryo neurons in culture. Formal quantitative analysis of MT assembly/disassembly indicated that none of the MTs in the axonal shaft were rapidly transported. Our results suggest that transport of axonal MTs is not required for delivery of newly synthesized tubulin to the growing nerve processes.
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Affiliation(s)
- Yitao Ma
- Department of Physiology and Biophysics, M/C 901, University of Illinois at Chicago, 835 South Wolcott Avenue, Chicago, IL 60612, USA
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45
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Rao MV, Campbell J, Yuan A, Kumar A, Gotow T, Uchiyama Y, Nixon RA. The neurofilament middle molecular mass subunit carboxyl-terminal tail domains is essential for the radial growth and cytoskeletal architecture of axons but not for regulating neurofilament transport rate. J Cell Biol 2003; 163:1021-31. [PMID: 14662746 PMCID: PMC2173612 DOI: 10.1083/jcb.200308076] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2003] [Accepted: 10/17/2003] [Indexed: 11/26/2022] Open
Abstract
The phosphorylated carboxyl-terminal "tail" domains of the neurofilament (NF) subunits, NF heavy (NF-H) and NF medium (NF-M) subunits, have been proposed to regulate axon radial growth, neurofilament spacing, and neurofilament transport rate, but direct in vivo evidence is lacking. Because deletion of the tail domain of NF-H did not alter these axonal properties (Rao, M.V., M.L. Garcia, Y. Miyazaki, T. Gotow, A. Yuan, S. Mattina, C.M. Ward, N.S. Calcutt, Y. Uchiyama, R.A. Nixon, and D.W. Cleveland. 2002. J. Cell Biol. 158:681-693), we investigated possible functions of the NF-M tail domain by constructing NF-M tail-deleted (NF-MtailDelta) mutant mice using an embryonic stem cell-mediated "gene knockin" approach that preserves normal ratios of the three neurofilament subunits. Mutant NF-MtailDelta mice exhibited severely inhibited radial growth of both motor and sensory axons. Caliber reduction was accompanied by reduced spacing between neurofilaments and loss of long cross-bridges with no change in neurofilament protein content. These observations define distinctive functions of the NF-M tail in regulating axon caliber by modulating the organization of the neurofilament network within axons. Surprisingly, the average rate of axonal transport of neurofilaments was unaltered despite these substantial effects on axon morphology. These results demonstrate that NF-M tail-mediated interactions of neurofilaments, independent of NF transport rate, are critical determinants of the size and cytoskeletal architecture of axons, and are mediated, in part, by the highly phosphorylated tail domain of NF-M.
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Affiliation(s)
- Mala V Rao
- Nathan Kline Institute, NYU School of Medicine, 140 Old Orangeburg Rd., Orangeburg, NY 10962, USA.
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46
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Rao MV, Nixon RA. Defective neurofilament transport in mouse models of amyotrophic lateral sclerosis: a review. Neurochem Res 2003; 28:1041-7. [PMID: 12737529 DOI: 10.1023/a:1023259207015] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Neurofilament proteins synthesized in the cell body of neurons are assembled and transported into axons, where they influence axon radial growth, axonal transport, and nerve conduction velocities. In diseased states, neurofilaments accumulate in cell bodies and proximal axons of affected neurons, and these lesions are characteristic of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), spinal muscular atrophy (SMA), Charcot-Marie-Tooth disease type 2 (CMT2), and hereditary sensory motor neuropathy. Although the molecular mechanisms that contribute to these accumulations are not yet identified, transgenic mouse models are beginning to provide insight into the role of neurofilament transport in disease-related dysfunction of neurons. This review addresses axonal transport in mouse models of ALS and the special significance of neurofilament transport in this disease.
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Affiliation(s)
- Mala V Rao
- Center for Dementia Research, Nathan Kline Institute/Department of Psychiatry, NYU School of Medicine, 140 Old Orangeburg Road, Orangeburg, New York 10962, USA.
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47
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Abstract
The classic view of slow axonal transport maintains that microtubules, neurofilaments, and actin filaments move down the axon relatively coherently at rates significantly slower than those characteristic of known motor proteins. Recent studies indicate that the movement of these cytoskeletal polymers is actually rapid, asynchronous, intermittent, and most probably fueled by familiar motors such as kinesins, myosins, and cytoplasmic dynein. This new view, which is supported by both live-cell imaging and mechanistic analyses, suggests that slow axonal transport is both rapid and plastic, and hence could underlie transformations in neuronal morphology.
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Affiliation(s)
- Peter W Baas
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
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48
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Abstract
Cytoskeletal and cytosolic proteins are transported along axons in the slow components of axonal transport at average rates of about 0.002-0.1 microm/s. This movement is essential for axonal growth and survival, yet the mechanism is poorly understood. Many studies on slow axonal transport have focused on tubulin, the subunit protein of microtubules, but attempts to observe the movement of this protein in cultured nerve cells have been largely unsuccessful. Here, we report direct observations of the movement of microtubules in cultured nerve cells using a modified fluorescence photobleaching strategy combined with difference imaging. The movements are rapid, with average rates of 1 microm/s, but they are also infrequent and highly asynchronous. These observations indicate that microtubules are propelled along axons by fast motors. We propose that the overall rate of movement is slow because the microtubules spend only a small proportion of their time moving. The rapid, infrequent, and highly asynchronous nature of the movement may explain why the axonal transport of tubulin has eluded detection in so many other studies.
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Affiliation(s)
- Lei Wang
- Graduate Program in Biological Sciences, Ohio University, Athens 45701, USA
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49
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Rao MV, Garcia ML, Miyazaki Y, Gotow T, Yuan A, Mattina S, Ward CM, Calcutt NA, Uchiyama Y, Nixon RA, Cleveland DW. Gene replacement in mice reveals that the heavily phosphorylated tail of neurofilament heavy subunit does not affect axonal caliber or the transit of cargoes in slow axonal transport. J Cell Biol 2002; 158:681-93. [PMID: 12186852 PMCID: PMC2174004 DOI: 10.1083/jcb.200202037] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2002] [Revised: 06/24/2002] [Accepted: 06/25/2002] [Indexed: 11/22/2022] Open
Abstract
The COOH-terminal tail of mammalian neurofilament heavy subunit (NF-H), the largest neurofilament subunit, contains 44-51 lysine-serine-proline repeats that are nearly stoichiometrically phosphorylated after assembly into neurofilaments in axons. Phosphorylation of these repeats has been implicated in promotion of radial growth of axons, control of nearest neighbor distances between neurofilaments or from neurofilaments to other structural components in axons, and as a determinant of slow axonal transport. These roles have now been tested through analysis of mice in which the NF-H gene was replaced by one deleted in the NF-H tail. Loss of the NF-H tail and all of its phosphorylation sites does not affect the number of neurofilaments, alter the ratios of the three neurofilament subunits, or affect the number of microtubules in axons. Additionally, it does not reduce interfilament spacing of most neurofilaments, the speed of action potential propagation, or mature cross-sectional areas of large motor or sensory axons, although its absence slows the speed of acquisition of normal diameters. Most surprisingly, at least in optic nerve axons, loss of the NF-H tail does not affect the rate of transport of neurofilament subunits.
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Affiliation(s)
- Mala V Rao
- Nathan Kline Institute, New York University School of Medicine, Orangeburg, NY 10962, USA.
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50
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Giuditta A, Kaplan BB, van Minnen J, Alvarez J, Koenig E. Axonal and presynaptic protein synthesis: new insights into the biology of the neuron. Trends Neurosci 2002; 25:400-4. [PMID: 12127756 DOI: 10.1016/s0166-2236(02)02188-4] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The presence of a local mRNA translation system in axons and terminals was proposed almost 40 years ago. Over the ensuing period, an impressive body of evidence has grown to support this proposal -- yet the nerve cell body is still considered to be the only source of axonal and presynaptic proteins. To dispel this lingering neglect, we now present the wealth of recent observations bearing on this central idea, and consider their impact on our understanding of the biology of the neuron. We demonstrate that extrasomatic translation sites, which are now well recognized in dendrites, are also present in axonal and presynaptic compartments.
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Affiliation(s)
- Antonio Giuditta
- Department of General and Environmental Physiology, University of Naples Federico II, Naples, Italy.
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