251
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Fukui H, Hanaoka R, Kawahara A. Noncanonical activity of seryl-tRNA synthetase is involved in vascular development. Circ Res 2009; 104:1253-9. [PMID: 19423848 DOI: 10.1161/circresaha.108.191189] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Vascular endothelial growth factor (Vegf) plays central roles in the establishment of stereotypic vascular patterning in vertebrates. However, it is not fully understood how the network of blood vessels is established and maintained during vascular development. A zebrafish ko095 mutant presented the disorganized vessels with abnormal branching of the established intersegmental vessels (ISVs) after 60 hours postfertilization. The gene responsible for ko095 encodes seryl-tRNA synthetase (Sars) with a nonsense mutation. The abnormal branching of ISVs in ko095 mutant was suppressed by the introduction of either wild-type Sars or a mutant Sars (T429A) lacking the enzymatic activity that catalyzes aminoacylation of transfer RNA for serine (canonical activity), suggesting that the abnormal branching is attributable to the loss of function of Sars besides its canonical activity. We further found the increased expression of vegfa in ko095 mutant at 72 hours postfertilization, which was also reversed by the introduction of Sars (T429A). Furthermore, the abnormal branching of ISVs in the mutant was suppressed by knockdown of vegfa or vegfr2 (kdra and kdrb). Knockdown of vegfc or vegfr3 rescued the abnormal ISV branching in ko095 mutant. These results suggest that the abnormal ISV branching in ko095 mutant is caused by the activated Vegfa-Vegfr2 signal and requires the Vegfc-Vegfr3 signal, because the latter is needed for general angiogenesis. Hence, we conclude that noncanonical activity of Sars is involved in vascular development presumably by modulating the expression of vegfa.
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Affiliation(s)
- Hajime Fukui
- Department of Structural Analysis, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
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252
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de Planell-Saguer M, Schroeder DG, Rodicio MC, Cox GA, Mourelatos Z. Biochemical and genetic evidence for a role of IGHMBP2 in the translational machinery. Hum Mol Genet 2009; 18:2115-26. [PMID: 19299493 DOI: 10.1093/hmg/ddp134] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The human motor neuron degenerative disease spinal muscular atrophy with respiratory distress type 1 (SMARD1) is caused by loss of function mutations of immunoglobulin mu-binding protein 2 (IGHMBP2), a protein of unknown function that contains DNA/RNA helicase and nucleic acid-binding domains. Reduced IGHMBP2 protein levels in neuromuscular degeneration (nmd) mice, the mouse model of SMARD1, lead to motor neuron degeneration. We report the biochemical characterization of IGHMBP2 and the isolation of a modifier locus that rescues the phenotype and motor neuron degeneration of nmd mice. We find that a 166 kb BAC transgene derived from CAST/EiJ mice and containing tRNA genes and activator of basal transcription 1 (Abt1), a protein-coding gene that is required for ribosome biogenesis, contains the genetic modifier responsible for motor neuron rescue. Our biochemical investigations show that IGHMBP2 associates physically with tRNAs and in particular with tRNA(Tyr), which are present in the modifier and with the ABT1 protein. We find that transcription factor IIIC-220 kDa (TFIIIC220), an essential factor required for tRNA transcription, and the helicases Reptin and Pontin, which function in transcription and in ribosome biogenesis, are also part of IGHMBP2-containing complexes. Our findings strongly suggest that IGHMBP2 is a component of the translational machinery and that these components can be manipulated genetically to suppress motor neuron degeneration.
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Affiliation(s)
- Mariàngels de Planell-Saguer
- Department of Pathology and Laboratory Medicine, Division of Neuropathology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6100, USA
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253
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Vuppalanchi D, Willis DE, Twiss JL. Regulation of mRNA transport and translation in axons. Results Probl Cell Differ 2009; 48:193-224. [PMID: 19582411 DOI: 10.1007/400_2009_16] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Movement of mRNAs into axons occurs by active transport by microtubules through the activity of molecular motor proteins. mRNAs are sequestered into granular-like particles, referred to as transport ribonucleoprotein particles (RNPs) that mediate transport into the axonal compartment. The interaction of mRNA binding proteins with targeted mRNA is a key event in regulating axonal mRNA localization and subsequent localized translation of mRNAs. Several growth-modulating stimuli have been shown to regulate axonal mRNA localization. These do so by activating specific intracellular signaling pathways that converge upon RNA binding proteins and other components of the transport RNP to regulate their activity specifically. Transport can be both positively and negatively regulated by individual stimuli with regard to individual mRNAs. Consequently, there is exquisite specificity for regulating the axon's composition of mRNAs and proteins that control expression in the axon. Finally, recent studies indicate that axotomy can also trigger changes in axonal mRNA composition by specifically shifting the populations of mRNAs that are transported into distal axons.
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254
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Abstract
Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed, essential enzymes responsible for performing the first step of protein synthesis. Specifically, ARSs attach amino acids to their cognate tRNA molecules in the cytoplasm and mitochondria. Recent studies have demonstrated that mutations in genes encoding ARSs can result in neurodegeneration, raising many questions about the role of these enzymes (and protein synthesis in general) in neuronal function. In this review, we summarize the current knowledge of genetic diseases that are associated with mutations in ARS-encoding genes, discuss the potential pathogenic mechanisms underlying these disorders, and point to likely areas of future research that will advance our understanding about the role of ARSs in genetic diseases.
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Affiliation(s)
- Anthony Antonellis
- Genome Technology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
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255
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Quality control despite mistranslation caused by an ambiguous genetic code. Proc Natl Acad Sci U S A 2008; 105:16502-7. [PMID: 18946032 DOI: 10.1073/pnas.0809179105] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A high level of accuracy during protein synthesis is considered essential for life. Aminoacyl-tRNA synthetases (aaRSs) translate the genetic code by ensuring the correct pairing of amino acids with their cognate tRNAs. Because some aaRSs also produce misacylated aminoacyl-tRNA (aa-tRNA) in vivo, we addressed the question of protein quality within the context of missense suppression by Cys-tRNA(Pro), Ser-tRNA(Thr), Glu-tRNA(Gln), and Asp-tRNA(Asn). Suppression of an active-site missense mutation leads to a mixture of inactive mutant protein (from translation with correctly acylated aa-tRNA) and active enzyme indistinguishable from the wild-type protein (from translation with misacylated aa-tRNA). Here, we provide genetic and biochemical evidence that under selective pressure, Escherichia coli not only tolerates the presence of misacylated aa-tRNA, but can even require it for growth. Furthermore, by using mass spectrometry of a reporter protein not subject to selection, we show that E. coli can survive the ambiguous genetic code imposed by misacylated aa-tRNA tolerating up to 10% of mismade protein. The editing function of aaRSs to hydrolyze misacylated aa-tRNA is not essential for survival, and the EF-Tu barrier against misacylated aa-tRNA is not absolute. Rather, E. coli copes with mistranslation by triggering the heat shock response that stimulates nonoptimized polypeptides to achieve a native conformation or to be degraded. In this way, E. coli ensures the presence of sufficient functional protein albeit at a considerable energetic cost.
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256
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Abstract
Aminoacylation of transfer RNAs establishes the rules of the genetic code. The reactions are catalyzed by an ancient group of 20 enzymes (one for each amino acid) known as aminoacyl tRNA synthetases (AARSs). Surprisingly, the etiology of specific diseases-including cancer, neuronal pathologies, autoimmune disorders, and disrupted metabolic conditions-is connected to specific aminoacyl tRNA synthetases. These connections include heritable mutations in the genes for tRNA synthetases that are causally linked to disease, with both dominant and recessive disease-causing mutations being annotated. Because some disease-causing mutations do not affect aminoacylation activity or apparent enzyme stability, the mutations are believed to affect functions that are distinct from aminoacylation. Examples include enzymes that are secreted as procytokines that, after activation, operate in pathways connected to the immune system or angiogenesis. In addition, within cells, synthetases form multiprotein complexes with each other or with other regulatory factors and in that way control diverse signaling pathways. Although much has been uncovered in recent years, many novel functions, disease connections, and interpathway connections of tRNA synthetases have yet to be worked out.
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257
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Abstract
Aminoacyl-tRNA synthetase mutations have been linked to neurological diseases, but aminoacylation may be unaffected. This protein superfamily also performs many other diverse functions. Yang et al. insightfully engineer a single mutation to unmask a cell signaling activity of tyrosyl-tRNA synthetase.
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Affiliation(s)
- Susan A Martinis
- Department of Biochemistry, 419 Roger Adams Laboratory, Box B-4, 600 South Mathews Avenue, University of Illinois-Urbana, Urbana, IL 61801, USA.
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258
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Yang XL, Kapoor M, Otero FJ, Slike BM, Tsuruta H, Frausto R, Bates A, Ewalt KL, Cheresh DA, Schimmel P. Gain-of-function mutational activation of human tRNA synthetase procytokine. ACTA ACUST UNITED AC 2008; 14:1323-33. [PMID: 18096501 DOI: 10.1016/j.chembiol.2007.10.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 09/19/2007] [Accepted: 10/26/2007] [Indexed: 10/22/2022]
Abstract
Disease-causing mutations occur in genes for aminoacyl tRNA synthetases. That some mutations are dominant suggests a gain of function. Native tRNA synthetases, such as tyrosyl-tRNA synthetase (TyrRS) and tryptophanyl-tRNA synthetase, catalyze aminoacylation and are also procytokines that are activated by natural fragmentation. In principle, however, gain-of-function phenotypes could arise from mutational activation of synthetase procytokines. From crystal structure analysis, we hypothesized that a steric block of a critical Glu-Leu-Arg (ELR) motif in full-length TyrRS suppresses the cytokine activity of a natural fragment. To test this hypothesis, we attempted to uncover ELR in the procytokine by mutating a conserved tyrosine (Y341) that tethers ELR. Site-specific proteolytic cleavage and small-angle X-ray scattering established subtle opening of the structure by the mutation. Strikingly, four different assays demonstrated mutational activation of cytokine functions. The results prove the possibilities for constitutive gain-of-function mutations in tRNA synthetases.
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Affiliation(s)
- Xiang-Lei Yang
- Department of Molecular Biology and Chemistry and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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259
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Barisic N, Claeys KG, Sirotković-Skerlev M, Löfgren A, Nelis E, De Jonghe P, Timmerman V. Charcot-Marie-Tooth disease: a clinico-genetic confrontation. Ann Hum Genet 2008; 72:416-41. [PMID: 18215208 DOI: 10.1111/j.1469-1809.2007.00412.x] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Charcot-Marie-Tooth disease (CMT) is the most common neuromuscular disorder. It represents a group of clinically and genetically heterogeneous inherited neuropathies. Here, we review the results of molecular genetic investigations and the clinical and neurophysiological features of the different CMT subtypes. The products of genes associated with CMT phenotypes are important for the neuronal structure maintenance, axonal transport, nerve signal transduction and functions related to the cellular integrity. Identifying the molecular basis of CMT and studying the relevant genes and their functions is important to understand the pathophysiological mechanisms of these neurodegenerative disorders, and the processes involved in the normal development and function of the peripheral nervous system. The results of molecular genetic investigations have impact on the appropriate diagnosis, genetic counselling and possible new therapeutic options for CMT patients.
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Affiliation(s)
- N Barisic
- Department of Pediatrics, Zagreb University Medical School, Zagreb, Croatia.
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260
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Greenberg Y, King M, Kiosses WB, Ewalt K, Yang X, Schimmel P, Reader JS, Tzima E. The novel fragment of tyrosyl tRNA synthetase, mini-TyrRS, is secreted to induce an angiogenic response in endothelial cells. FASEB J 2007; 22:1597-605. [PMID: 18165356 DOI: 10.1096/fj.07-9973com] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Aminoacyl tRNA synthetases--enzymes that catalyze the first step of protein synthesis--in mammalian cells are now known to have expanded functions, including activities in signal transduction pathways, such as those for angiogenesis and inflammation. The native synthetases themselves are procytokines, having no signal transduction activities. After alternative splicing or natural proteolysis, specific fragments that are potent cytokines and that interact with specific receptors on cell surfaces are released. In this manner, a natural fragment of human tyrosyl tRNA synthetase (TyrRS), mini-TyrRS, has been shown to act as a proangiogenic cytokine. The mechanistic basis for the action of mini-TyrRS in angiogenesis has yet to be established. Here, we show that mini-TyrRS is exported from endothelial cells when they are treated with tumor necrosis factor-alpha. Mini-TyrRS binds to vascular endothelial cells and activates an array of angiogenic signal transduction pathways. Mini-TyrRS-induced angiogenesis requires the activation of vascular endothelial growth factor receptor-2 (VEGFR2/Flk-1/KDR). Mini-TyrRS stimulates VEGFR2 phosphorylation in a VEGF-independent manner, suggesting VEGFR2 transactivation. Transactivation of VEGFR2 and downstream angiogenesis require an intact Glu-Leu-Arg (ELR) motif in mini-TyrRS, which is important for its cytokine activity. These studies therefore suggest a mechanism by which mini-TyrRS induces angiogenesis in endothelial cells and provide further insight into the role of mini-TyrRS as a link between translation and angiogenesis.
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Affiliation(s)
- Y Greenberg
- Department of Cell and Molecular Physiology, University of North Carolina, Chapel Hill, 103 Mason Farm Rd., Chapel Hill, NC 27599-7545, USA
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261
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Ataide SF, Wilson SN, Dang S, Rogers TE, Roy B, Banerjee R, Henkin TM, Ibba M. Mechanisms of resistance to an amino acid antibiotic that targets translation. ACS Chem Biol 2007; 2:819-27. [PMID: 18154269 DOI: 10.1021/cb7002253] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Structural and functional diversity among the aminoacyl-tRNA synthetases prevent infiltration of the genetic code by noncognate amino acids. To explore whether these same features distinguish the synthetases as potential sources of resistance against antibiotic amino acid analogues, we investigated bacterial growth inhibition by S-(2-aminoethyl)-L-cysteine (AEC). Wild-type lysyl-tRNA synthetase (LysRS) and a series of active site variants were screened for their ability to restore growth of an Escherichia coli LysRS null strain at increasing concentrations of AEC. While wild-type E. coli growth is completely inhibited at 5 microM AEC, two LysRS variants, Y280F and F426W, provided substantial resistance and allowed E. coli to grow in the presence of up to 1 mM AEC. Elevated resistance did not reflect changes in the kinetics of amino acid activation or tRNA (Lys) aminoacylation, which showed at best 4-6-fold improvements, but instead correlated with the binding affinity for AEC, which was decreased approximately 50-fold in the LysRS variants. In addition to changes in LysRS, AEC resistance has also been attributed to mutations in the L box riboswitch, which regulates expression of the lysC gene, encoding aspartokinase. The Y280F and F426W LysRS mutants contained wild-type L box riboswitches that responded normally to AEC in vitro, indicating that LysRS is the primary cellular target of this antibiotic. These findings suggest that the AEC resistance conferred by L box mutations is an indirect effect resulting from derepression of lysC expression and increased cellular pools of lysine, which results in more effective competition with AEC for binding to LysRS.
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Affiliation(s)
| | | | | | | | - Bappaditya Roy
- Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology, University of Calcutta, Kolkata, 700 019 West Bengal, India
| | - Rajat Banerjee
- Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology, University of Calcutta, Kolkata, 700 019 West Bengal, India
| | - Tina M. Henkin
- Department of Microbiology
- Ohio State Biochemistry Program
- Ohio State RNA Group
| | - Michael Ibba
- Department of Microbiology
- Ohio State Biochemistry Program
- Ohio State RNA Group
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262
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Goryunov D, Nightingale A, Bornfleth L, Leung C, Liem RKH. Multiple disease-linked myotubularin mutations cause NFL assembly defects in cultured cells and disrupt myotubularin dimerization. J Neurochem 2007; 104:1536-52. [PMID: 17973976 DOI: 10.1111/j.1471-4159.2007.05103.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Charcot-Marie-Tooth disease (CMT) is an inherited peripheral neuropathy that has been linked to mutations in multiple genes. Mutations in the neurofilament light (NFL) chain gene lead to the CMT2E form whereas mutations in the myotubularin-related protein 2 and 13 (MTMR2 and MTMR13) genes lead to the CMT4B form. These two forms share characteristic pathological hallmarks on nerve biopsies including concentric sheaths ('onion bulbs') and, in at least one case, myelin loops. In addition, MTMR2 protein has been shown to interact physically with both NFL and MTMR13. Here, we present evidence that CMT-linked mutations of MTMR2 can cause NFL aggregation in a cell line devoid of endogenous intermediate filaments, SW13vim(-). Mutations in the protein responsible for X-linked myotubular myopathy (myotubularin, MTM1) also induced NFL abnormalities in these cells. We also show that two MTMR2 mutant proteins, G103E and R283W, are unable to form dimers and undergo phosphorylation in vivo, implicating impaired complex formation in myotubularin-related pathology.
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Affiliation(s)
- Dmitry Goryunov
- Department of Pathology and Cell Biology, Columbia University College of Physicians & Surgeons, New York, New York 10032, USA
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263
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Cañete-Soler R, Schlaepfer WW. The complex relation between genotype and phenotype in motor neuron disease. Ann Neurol 2007; 62:8-14. [PMID: 17469207 DOI: 10.1002/ana.21128] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The success in mapping genetic loci and identifying mutant genes in familial neurodegenerative disease has outpaced our ability to understand the linkage between genotype and phenotype of disease. The results have led to a backlog of genetic information with limited clarification of underlying disease mechanisms. A major dilemma is how mutations in widely expressed proteins lead to degeneration or dysfunction of small subsets of neurons. The problem raises fundamental questions as to the nature and interrelation of pathways that maintain the homeostasis of differentiated neurons. The issue also bears on the pathogenesis of sporadic forms of disease and prospective efficacy of therapeutic applications. This review examines the problem as it relates to motor neuron disease.
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Affiliation(s)
- Rafaela Cañete-Soler
- Division of Neuropathology, University of Pennsylvania Medical School, Philadelphia, PA 19104, USA
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264
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Wang W, van Niekerk E, Willis DE, Twiss JL. RNA transport and localized protein synthesis in neurological disorders and neural repair. Dev Neurobiol 2007; 67:1166-82. [PMID: 17514714 DOI: 10.1002/dneu.20511] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Neural cells are able to finely tune gene expression through post-transcriptional mechanisms. Localization of mRNAs to subcellular regions has been detected in neurons, oligodendrocytes, and astrocytes providing these domains with a locally renewable source of proteins. Protein synthesis in dendrites has most frequently been associated with synaptic plasticity, while axonally synthesized proteins appear to facilitate pathfinding and injury responses. For oligodendrocytes, mRNAs encoding several proteins for myelin formation are locally generated suggesting that this mechanism assists in myelination. Astrocytic processes have not been well studied but localization of GFAP mRNA has been demonstrated. Both RNA transport and localized translation are regulated processes. RNA transport appears to be highly selective and, at least in part, the destiny of individual mRNAs is determined in the nucleus. RNA-protein and protein-protein interactions determine which mRNAs are targeted to subcellular regions. Several RNA binding proteins that drive mRNA localization have also been shown to repress translation during transport. Activity of the translational machinery is also regulated in distal neural cell processes. Clinically, disruption of mRNA localization and/or localized mRNA translation may contribute to pathophysiology of fragile X mental retardation and spinal muscular atrophy. Axonal injury has been shown to activate localized protein synthesis, providing both a means to initiate regeneration and retrogradely signal injury to the cell body. Decreased capacity to transport mRNAs and translational machinery into distal processes could jeopardize the ability to respond to injury or local stimuli within axons and dendrites.
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Affiliation(s)
- Wenlan Wang
- Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, Delaware 19803, USA
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265
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Lambrechts D, Robberecht W, Carmeliet P. Heterogeneity in motoneuron disease. Trends Neurosci 2007; 30:536-44. [PMID: 17825438 DOI: 10.1016/j.tins.2007.07.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Revised: 07/10/2007] [Accepted: 07/16/2007] [Indexed: 12/11/2022]
Abstract
Recently, mutations in several genes have been identified as primary causes for the degeneration of motoneurons and their axons. Strikingly, mutations in the same genes were associated with clinically different motoneuron syndromes. The identity of these genes also shed light on the mechanisms of motoneuron degeneration and revealed that overlapping motoneuron phenotypes might be caused by heterogeneous molecular mechanisms. Overall, these findings have challenged the diagnostic classification system set by clinical judgement and triggered the notion of heterogeneity in motoneuron disease. It will now be especially relevant to identify the mechanisms and principles that motoneuron diseases have in common, as this will allow us to identify the most relevant therapeutic targets. On the other hand, heterogeneity in motoneuron disease also implies that finding a monotherapy cure for motoneuron disease will be challenging and that pre-clinical testing of therapeutic targets should not be limited to a single animal model.
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Affiliation(s)
- Diether Lambrechts
- The Center for Transgene Technology and Gene Therapy, K.U. Leuven, B-3000, Leuven, Belgium
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266
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Nave KA, Sereda MW, Ehrenreich H. Mechanisms of disease: inherited demyelinating neuropathies--from basic to clinical research. ACTA ACUST UNITED AC 2007; 3:453-64. [PMID: 17671523 DOI: 10.1038/ncpneuro0583] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2007] [Accepted: 05/25/2007] [Indexed: 01/30/2023]
Abstract
The hereditary motor and sensory neuropathies (also known as Charcot-Marie-Tooth disease or CMT) are characterized by a length-dependent loss of axonal integrity in the PNS, which leads to progressive muscle weakness and sensory deficits. The 'demyelinating' neuropathies (CMT disease types 1 and 4) are genetically heterogeneous, but their common feature is that the primary defect perturbs myelination. As we discuss in this Review, several new genes associated with CMT1 and CMT4 have recently been identified. The emerging view is that a range of different subcellular defects in Schwann cells can cause axonal loss, which represents the final common pathway of all CMT disease and is independent of demyelination. We propose that Schwann cells provide a first line of axonal neuroprotection. A better understanding of axon-glia interactions should open the way to therapeutic interventions for demyelinating neuropathies. Transgenic animal models have become essential for dissecting CMT disease mechanisms and exploring novel therapies.
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Affiliation(s)
- Klaus-Armin Nave
- Department of Neurogenetics, Max Planck Institute of Experimental Medicine, Göttingen, Germany.
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267
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Scheper GC, van der Knaap MS, Proud CG. Translation matters: protein synthesis defects in inherited disease. Nat Rev Genet 2007; 8:711-23. [PMID: 17680008 DOI: 10.1038/nrg2142] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The list of genetic diseases caused by mutations that affect mRNA translation is rapidly growing. Although protein synthesis is a fundamental process in all cells, the disease phenotypes show a surprising degree of heterogeneity. Studies of some of these diseases have provided intriguing new insights into the functions of proteins involved in the process of translation; for example, evidence suggests that several have other functions in addition to their roles in translation. Given the numerous proteins involved in mRNA translation, it is likely that further inherited diseases will turn out to be caused by mutations in genes that are involved in this complex process.
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Affiliation(s)
- Gert C Scheper
- Department of Child Neurology/Center for Neurogenomics and Cognitive Research, Vrije Universiteit Medical Center, De Boelelaan 1117, 1081HV Amsterdam, The Netherlands
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268
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van Niekerk EA, Willis DE, Chang JH, Reumann K, Heise T, Twiss JL. Sumoylation in axons triggers retrograde transport of the RNA-binding protein La. Proc Natl Acad Sci U S A 2007; 104:12913-8. [PMID: 17646655 PMCID: PMC1937566 DOI: 10.1073/pnas.0611562104] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
A surprisingly large population of mRNAs has been shown to localize to sensory axons, but few RNA-binding proteins have been detected in these axons. These axonal mRNAs include several potential binding targets for the La RNA chaperone protein. La is transported into axonal processes in both culture and peripheral nerve. Interestingly, La is posttranslationally modified in sensory neurons by sumoylation. In axons, small ubiquitin-like modifying polypeptides (SUMO)-La interacts with dynein, whereas native La interacts with kinesin. Lysine 41 is required for sumoylation, and sumoylation-incompetent La(K41R) shows only anterograde transport, whereas WT La shows both anterograde and retrograde transport in axons. Thus, sumoylation of La determines the directionality of its transport within the axonal compartment, with SUMO-La likely recycling to the cell body.
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Affiliation(s)
- Erna A. van Niekerk
- *Department of Biological Sciences, University of Delaware, Newark, DE 19713
| | - Dianna E. Willis
- Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, DE 19803
| | - Jay H. Chang
- Neural Development and Plasticity Section, Laboratory of Cellular and Synaptic Neurophysiology, National Institute of Child Health and Human Development–National Institutes of Health, Bethesda, MD 20892
| | - Kerstin Reumann
- Heinrich Pette Institute for Experimental Virology and Immunology, University of Hamburg, D-20251 Hamburg, Germany; and
| | - Tilman Heise
- Heinrich Pette Institute for Experimental Virology and Immunology, University of Hamburg, D-20251 Hamburg, Germany; and
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425
| | - Jeffery L. Twiss
- *Department of Biological Sciences, University of Delaware, Newark, DE 19713
- Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, DE 19803
- To whom correspondence should be addressed. E-mail:
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269
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Nangle LA, Zhang W, Xie W, Yang XL, Schimmel P. Charcot-Marie-Tooth disease-associated mutant tRNA synthetases linked to altered dimer interface and neurite distribution defect. Proc Natl Acad Sci U S A 2007; 104:11239-44. [PMID: 17595294 PMCID: PMC2040883 DOI: 10.1073/pnas.0705055104] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Charcot-Marie-Tooth (CMT) diseases are the most common heritable peripheral neuropathy. At least 10 different mutant alleles of GARS (the gene for glycyl-tRNA synthetase) have been reported to cause a dominant axonal form of CMT (type 2D). A unifying connection between these mutations and CMT has been unclear. Here, mapping mutations onto the recently determined crystal structure of human GlyRS showed them within a band encompassing both sides of the dimer interface, with two CMT-causing mutations being at sites that are complementary partners of a "kissing" contact across the dimer interface. The CMT phenotype is shown here to not correlate with aminoacylation activity. However, most mutations affect dimer formation (to enhance or weaken). Seven CMT-causing variants and the wild-type protein were expressed in transfected neuroblastoma cells that sprout primitive neurites. Wild-type GlyRS distributed into the nascent neurites and was associated with normal neurite sprouting. In contrast, all mutant proteins were distribution-defective. Thus, CMT-causing mutations of GlyRS share a common defect in localization. This defect may be connected in some way to a change in the surfaces at the dimer interface.
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Affiliation(s)
- Leslie A. Nangle
- The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Wei Zhang
- The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Wei Xie
- The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Xiang-Lei Yang
- The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
- *To whom correspondence may be addressed. E-mail: or
| | - Paul Schimmel
- The Skaggs Institute for Chemical Biology and the Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
- *To whom correspondence may be addressed. E-mail: or
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270
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Xie W, Nangle LA, Zhang W, Schimmel P, Yang XL. Long-range structural effects of a Charcot-Marie-Tooth disease-causing mutation in human glycyl-tRNA synthetase. Proc Natl Acad Sci U S A 2007; 104:9976-81. [PMID: 17545306 PMCID: PMC1891255 DOI: 10.1073/pnas.0703908104] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Functional expansion of specific tRNA synthetases in higher organisms is well documented. These additional functions may explain why dominant mutations in glycyl-tRNA synthetase (GlyRS) and tyrosyl-tRNA synthetase cause Charcot-Marie-Tooth (CMT) disease, the most common heritable disease of the peripheral nervous system. At least 10 disease-causing mutant alleles of GlyRS have been annotated. These mutations scatter broadly across the primary sequence and have no apparent unifying connection. Here we report the structure of wild type and a CMT-causing mutant (G526R) of homodimeric human GlyRS. The mutation is at the site for synthesis of glycyl-adenylate, but the rest of the two structures are closely similar. Significantly, the mutant form diffracts to a higher resolution and has a greater dimer interface. The extra dimer interactions are located approximately 30 A away from the G526R mutation. Direct experiments confirm the tighter dimer interaction of the G526R protein. The results suggest the possible importance of subtle, long-range structural effects of CMT-causing mutations at the dimer interface. From analysis of a third crystal, an appended motif, found in higher eukaryote GlyRSs, seems not to have a role in these long-range effects.
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Affiliation(s)
- Wei Xie
- The Skaggs Institute for Chemical Biology and Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Leslie A. Nangle
- The Skaggs Institute for Chemical Biology and Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Wei Zhang
- The Skaggs Institute for Chemical Biology and Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Paul Schimmel
- The Skaggs Institute for Chemical Biology and Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
- *To whom correspondence may be addressed. E-mail: or
| | - Xiang-Lei Yang
- The Skaggs Institute for Chemical Biology and Department of Molecular Biology, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037
- *To whom correspondence may be addressed. E-mail: or
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271
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Cader MZ, Ren J, James PA, Bird LE, Talbot K, Stammers DK. Crystal structure of human wildtype and S581L-mutant glycyl-tRNA synthetase, an enzyme underlying distal spinal muscular atrophy. FEBS Lett 2007; 581:2959-64. [PMID: 17544401 DOI: 10.1016/j.febslet.2007.05.046] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2007] [Revised: 05/15/2007] [Accepted: 05/16/2007] [Indexed: 11/30/2022]
Abstract
Dominant mutations in the ubiquitous enzyme glycyl-tRNA synthetase (GlyRS), including S581L, lead to motor nerve degeneration. We have determined crystal structures of wildtype and S581L-mutant human GlyRS. The S581L mutation is approximately 50A from the active site, and yet gives reduced aminoacylation activity. The overall structures of wildtype and S581L-GlyRS, including the active site, are very similar. However, residues 567-575 of the anticodon-binding domain shift position and in turn could indirectly affect glycine binding via the tRNA or alternatively inhibit conformational changes. Reduced enzyme activity may underlie neuronal degeneration, although a dominant-negative effect is more likely in this autosomal dominant disorder.
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Affiliation(s)
- Muhammed Z Cader
- Henry Wellcome Building for Gene Function, MRC Functional Genetics Unit, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom
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272
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Chihara T, Luginbuhl D, Luo L. Cytoplasmic and mitochondrial protein translation in axonal and dendritic terminal arborization. Nat Neurosci 2007; 10:828-37. [PMID: 17529987 DOI: 10.1038/nn1910] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Accepted: 04/18/2007] [Indexed: 12/16/2022]
Abstract
We identified a mutation in Aats-gly (also known as gars or glycyl-tRNA synthetase), the Drosophila melanogaster ortholog of the human GARS gene that is associated with Charcot-Marie-Tooth neuropathy type 2D (CMT2D), from a mosaic genetic screen. Loss of gars in Drosophila neurons preferentially affects the elaboration and stability of terminal arborization of axons and dendrites. The human and Drosophila genes each encode both a cytoplasmic and a mitochondrial isoform. Using additional mutants that selectively disrupt cytoplasmic or mitochondrial protein translation, we found that cytoplasmic protein translation is required for terminal arborization of both dendrites and axons during development. In contrast, disruption of mitochondrial protein translation preferentially affects the maintenance of dendritic arborization in adults. We also provide evidence that human GARS shows equivalent functions in Drosophila, and that CMT2D causal mutations show loss-of-function properties. Our study highlights different demands of protein translation for the development and maintenance of axons and dendrites.
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Affiliation(s)
- Takahiro Chihara
- Howard Hughes Medical Institute, Department of Biological Sciences, 385 Serra Mall, Stanford University, Stanford, California 94305, USA
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273
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Scheper GC, van der Klok T, van Andel RJ, van Berkel CGM, Sissler M, Smet J, Muravina TI, Serkov SV, Uziel G, Bugiani M, Schiffmann R, Krägeloh-Mann I, Smeitink JAM, Florentz C, Van Coster R, Pronk JC, van der Knaap MS. Mitochondrial aspartyl-tRNA synthetase deficiency causes leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation. Nat Genet 2007; 39:534-9. [PMID: 17384640 DOI: 10.1038/ng2013] [Citation(s) in RCA: 341] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 02/23/2007] [Indexed: 11/08/2022]
Abstract
Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) has recently been defined based on a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy. LBSL is an autosomal recessive disease, most often manifesting in early childhood. Affected individuals develop slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. We performed linkage mapping with microsatellite markers in LBSL families and found a candidate region on chromosome 1, which we narrowed by means of shared haplotypes. Sequencing of genes in this candidate region uncovered mutations in DARS2, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals from all 30 families. Enzyme activities of mutant proteins were decreased. We were surprised to find that activities of mitochondrial complexes from fibroblasts and lymphoblasts derived from affected individuals were normal, as determined by different assays.
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Affiliation(s)
- Gert C Scheper
- Department of Pediatrics and Child Neurology, Vrije University Medical Center, 1081 HV Amsterdam, The Netherlands.
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274
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Nicholson G, Myers S. Intermediate forms of Charcot-Marie-Tooth neuropathy: a review. Neuromolecular Med 2007; 8:123-30. [PMID: 16775371 DOI: 10.1385/nmm:8:1-2:123] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 12/13/2005] [Accepted: 12/29/2005] [Indexed: 12/19/2022]
Abstract
The Charcot-Marie-Tooth (CMT) neuropathies divide into two main electrophysiological groups with slow and near normal conduction velocities corresponding to Schwann cell and axonal pathology. An intermediate group also exists with nerve conduction velocities, which overlaps the two main groups. Families with intermediate CMT can be recognized in which different affected individuals in the same family have motor conduction velocities in both the CMT type 1 and 2 ranges (i.e., above and below 38 m/s). The intermediate group is caused by a limited number of distinct gene mutations in dynamin2 (DNM2), gap-junction protein 1 (GJB1), neurofilament light polypeptide (NF-L) genes, and a rare mutation and as yet unknown genes on chromosome 1 and 10 loci. Intermediate forms of CMT may be associated with unique disease mechanisms affecting both Schwann cells and axons. It is useful to recognize this unique group of neuropathies for diagnostic and management purposes.
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Affiliation(s)
- Garth Nicholson
- University of Sydney, The Molecular Medicine and ANZAC Research Institute, Northcott Neuroscience Laboratory, Concord Hospital, NSW 2139, Australia.
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275
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Abstract
Neuropathy is one of the most common referrals to neurologic clinics. Patients often undergo extensive testing for acquired etiologies; inherited causes are common. Increasingly, genetic causes are becoming known and commercial testing available. The rate of recent discovery has been rapid and relates to the extent of single gene disorders of nerve, the ease of peripheral nervous system functional examination, and readily accessible pathologic tissue. Foremost in the rate of recent discoveries is the work and tools of the human genome project. the rapidity of the ongoing discovery requires clinicians to be familiar with molecular biologic discoveries and consider wisely which testing should be performed.
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Affiliation(s)
- Christopher J Klein
- Department of Neurology, Division of Peripheral Nerve Diseases, Mayo Clinic, Rochester, MN, USA.
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276
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Abstract
A major question in the pathogenesis of motor neuron disease is why motor neurons are selectively susceptible to mutations in widely expressed gene products. Reexamination of motor neuron degeneration due to alterations of neurofilament (NF) expression suggests that disruption of assembly with aggregation of the light neurofilament (NFL) protein may be an upstream event and contributing factor leading to the preferential degeneration of motor neurons. The implications of these findings are that aggregation of NFL is not only a triggering mechanism to account for the hallmark aggregates of NF protein in sporadic and familial forms of amyotrophic lateral sclerosis, but that aggregates of NFL may also promote aggregation of wildly expressed proteins that are destabilized by missense mutations, such as by mutations in superoxide dismutase-1 protein. This review examines the potential role of NFs in determining and promoting the preferential degeneration of motor neurons in motor neuron disease. The underlying premise is that motor neurons are selectively susceptible to alterations in NF expression, that alterations in NF expression lead to NF aggregates in motor neurons, and that elevated levels of NF aggregates provide a favorable microenvironment for the formation of neurotoxic aggregation and degeneration of motor neurons.
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Affiliation(s)
- Hong Lin
- Division of Neuropathology, University of Pennsylvania Medical School, Philadelphia, PA 19104-6100, USA
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277
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Braathen GJ, Sand JC, Russell MB. Symptomatic Charcot-Marie-Tooth? A pair of concordant monozygotic twins. Acta Neurol Scand 2006; 114:403-6. [PMID: 17083341 DOI: 10.1111/j.1600-0404.2006.00713.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND A pair of monozygotic twin brothers were referred due to hereditary peripheral neuropathy resembling late onset Charcot-Marie-Tooth (CMT). AIM OF THE STUDY Diagnostic classification of the twin pair. METHOD Clinical, neurological, genetical and neurophysiological examination, and molecular genetic testing. RESULTS The clinic and neurophysiology was compatible with CMT disease with late onset. Molecular genetic analysis excluded mutations in PMP22, connexin32, MPZ, LITAF and MFNZ genes, as well as duplication and deletion of PMP22. CONCLUSIONS The twins were employed in PVC production and developed symptoms after 14 years of massive exposure. We think that the heavy exposure to various neurotoxic compounds caused symptoms that mimic late-onset CMT. However, the twins had distal dysesthesia which is unusual in inherited neuropathies. This illustrates the importance of an occupational history even in the molecular genetic era.
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Affiliation(s)
- G J Braathen
- Faculty Division Akershus University Hospital, University of Oslo, Oslo, Norway.
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278
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Antonellis A, Lee-Lin SQ, Wasterlain A, Leo P, Quezado M, Goldfarb LG, Myung K, Burgess S, Fischbeck KH, Green ED. Functional analyses of glycyl-tRNA synthetase mutations suggest a key role for tRNA-charging enzymes in peripheral axons. J Neurosci 2006; 26:10397-406. [PMID: 17035524 PMCID: PMC6674701 DOI: 10.1523/jneurosci.1671-06.2006] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Charcot-Marie-Tooth disease type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V) are axonal neuropathies characterized by a phenotype that is more severe in the upper extremities. We previously implicated mutations in the gene encoding glycyl-tRNA synthetase (GARS) as the cause of CMT2D and dSMA-V. GARS is a member of the family of aminoacyl-tRNA synthetases responsible for charging tRNA with cognate amino acids; GARS ligates glycine to tRNA(Gly). Here, we present functional analyses of disease-associated GARS mutations and show that there are not any significant mutation-associated changes in GARS expression levels; that the majority of identified GARS mutations modeled in yeast severely impair viability; and that, in most cases, mutant GARS protein mislocalizes in neuronal cells. Indeed, four of the five mutations studied show loss-of-function features in at least one assay, suggesting that tRNA-charging deficits play a role in disease pathogenesis. Finally, we detected endogenous GARS-associated granules in the neurite projections of cultured neurons and in the peripheral nerve axons of normal human tissue. These data are particularly important in light of the recent identification of CMT-associated mutations in another tRNA synthetase gene [YARS (tyrosyl-tRNA synthetase gene)]. Together, these findings suggest that tRNA-charging enzymes play a key role in maintaining peripheral axons.
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Affiliation(s)
| | | | | | - Paul Leo
- Genetic Disease Research Branch, and
| | | | | | - Kyungjae Myung
- Genetics and Molecular Biology Branch, National Human Genome Research Institute
| | | | - Kenneth H. Fischbeck
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
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279
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Seburn KL, Nangle LA, Cox GA, Schimmel P, Burgess RW. An active dominant mutation of glycyl-tRNA synthetase causes neuropathy in a Charcot-Marie-Tooth 2D mouse model. Neuron 2006; 51:715-26. [PMID: 16982418 DOI: 10.1016/j.neuron.2006.08.027] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Revised: 08/11/2006] [Accepted: 08/23/2006] [Indexed: 11/22/2022]
Abstract
Of the many inherited Charcot-Marie-Tooth peripheral neuropathies, type 2D (CMT2D) is caused by dominant point mutations in the gene GARS, encoding glycyl tRNA synthetase (GlyRS). Here we report a dominant mutation in Gars that causes neuropathy in the mouse. Importantly, both sensory and motor axons are affected, and the dominant phenotype is not caused by a loss of the GlyRS aminoacylation function. Mutant mice have abnormal neuromuscular junction morphology and impaired transmission, reduced nerve conduction velocities, and a loss of large-diameter peripheral axons, without defects in myelination. The mutant GlyRS enzyme retains aminoacylation activity, and a loss-of-function allele, generated by a gene-trap insertion, shows no dominant phenotype in mice. These results indicate that the CMT2D phenotype is caused not by reduction of the canonical GlyRS activity and insufficiencies in protein synthesis, but instead by novel pathogenic roles for the mutant GlyRS that specifically affect peripheral neurons.
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Affiliation(s)
- Kevin L Seburn
- The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609, USA
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280
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Abstract
Mutations in GARS cause dominantly inherited neuropathies in humans. GARS encodes glycyl-tRNA synthetase, the enzyme that couples glycine to its tRNA. In this issue of Neuron, Seburn et al. have identified and characterized a mutant mouse with a dominantly inherited axonal neuropathy caused by a Gars mutation that is inferred to have a gain of function.
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Affiliation(s)
- Steven S Scherer
- Department of Neurology, 464 Stemmler Hall, University of Pennsylvania School of Medicine, Philadelphia, 19104, USA
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281
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Abstract
The number of genes associated with motor neuron degeneration has increased considerably over the past few years. As more gene mutations are identified, the hope arises that certain common themes and/or pathways become clear. In this overview, we focus on recent discoveries related to amyotrophic lateral sclerosis (ALS), spinal muscular atrophies (SMA), and distal hereditary motor neuropathies (dHMN). It is striking that many of the mutated genes that were linked to these diseases encode proteins that are either directly or indirectly involved in axonal transport or play a role in RNA metabolism. We hypothesize that both phenomena are not only crucial for the normal functioning of motor neurons, but that they could also be interconnected. In analogy with the situation after acute stress, axonal mRNA translation followed by retrograde transport of the signal back to the nucleus could play an important role in chronic motor neuron diseases. We hope that information on the genetic causes of these diseases and the insight into the pathologic processes involved could ultimately lead to therapeutic strategies that prevent or at least slow this degenerative process.
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Affiliation(s)
- Ludo Van Den Bosch
- Neurobiology, Campus Gasthuisberg O&N2 PB1022,Herestraat 49, B-3000 Leuven, Belgium.
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282
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Pasinelli P, Brown RH. Molecular biology of amyotrophic lateral sclerosis: insights from genetics. Nat Rev Neurosci 2006; 7:710-23. [PMID: 16924260 DOI: 10.1038/nrn1971] [Citation(s) in RCA: 828] [Impact Index Per Article: 46.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Amyotrophic lateral sclerosis (ALS) is a paralytic disorder caused by motor neuron degeneration. Mutations in more than 50 human genes cause diverse types of motor neuron pathology. Moreover, defects in five Mendelian genes lead to motor neuron disease, with two mutations reproducing the ALS phenotype. Analyses of these genetic effects have generated new insights into the diverse molecular pathways involved in ALS pathogenesis. Here, we present an overview of the mechanisms for motor neuron death and of the role of non-neuronal cells in ALS.
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Affiliation(s)
- Piera Pasinelli
- Day Neuromuscular Research Laboratory, Massachusetts General Hospital, Room 3125, Building 114, 16th Street, Navy Yard, Charlestown, Massachusetts 02429, USA
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283
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Abstract
The 3D structure of a protein is determined by the unique sequence of amino acid residues comprising the polypeptide chain. Sequence changes can cause protein misfolding, a potentially toxic phenomenon implicated in various neurodegenerative disorders. In a recent paper, translational misincorporation is proposed to be a new biochemical mechanism for generating mutant proteins that misfold and kill neurons.
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Affiliation(s)
- Jean-Christophe Rochet
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, Heine Pharmacy Building, 575 Stadium Mall Drive, West Lafayette, Indiana 47907-2091, USA.
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284
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Nangle LA, Motta CM, Schimmel P. Global Effects of Mistranslation from an Editing Defect in Mammalian Cells. ACTA ACUST UNITED AC 2006; 13:1091-100. [PMID: 17052613 DOI: 10.1016/j.chembiol.2006.08.011] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 08/28/2006] [Accepted: 08/28/2006] [Indexed: 12/28/2022]
Abstract
Aminoacyl-tRNA synthetases prevent mistranslation, or genetic code ambiguity, through specialized editing reactions. Mutations that disrupt editing in bacteria adversely affect cell growth and viability, and recent work in the mouse supports the idea that translational errors caused by an editing defect lead to a neurological disease-like phenotype. To further investigate the connection of mistranslation to cell pathology, we introduced an inducible transgene expressing an editing-deficient valyl-tRNA synthetase into mammalian cells. Introducing mistranslation precipitated a disruption of cell morphology and membrane blebbing, accompanied by activation of caspase-3, consistent with an apoptotic response. Addition of a noncanonical amino acid that is misactivated, but not cleared, by the editing-defective enzyme exacerbated these effects. A special ambiguity-detecting sensor provided direct readout of mistranslation in vivo, supporting the possibility that decreased translational fidelity could be associated with disease.
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Affiliation(s)
- Leslie A Nangle
- Department of Molecular Biology, The Skaggs Institute for Chemical Biology, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
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285
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James PA, Talbot K. The molecular genetics of non-ALS motor neuron diseases. Biochim Biophys Acta Mol Basis Dis 2006; 1762:986-1000. [PMID: 16765570 DOI: 10.1016/j.bbadis.2006.04.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Revised: 03/23/2006] [Accepted: 04/11/2006] [Indexed: 12/11/2022]
Abstract
Hereditary disorders of voluntary motor neurons are individually relatively uncommon, but have the potential to provide significant insights into motor neuron function in general and into the mechanisms underlying the more common form of sporadic Amyotrophic Lateral Sclerosis. Recently, mutations in a number of novel genes have been associated with Lower Motor Neuron (HSPB1, HSPB8, GARS, Dynactin), Upper Motor Neuron (Spastin, Atlastin, Paraplegin, HSP60, KIF5A, NIPA1) or mixed ALS-like phenotypes (Alsin, Senataxin, VAPB, BSCL2). In comparison to sporadic ALS these conditions are usually associated with slow progression, but as experience increases, a wide variation in clinical phenotype has become apparent. At the molecular level common themes are emerging that point to areas of specific vulnerability for motor neurons such as axonal transport, endosomal trafficking and RNA processing. We review the clinical and molecular features of this diverse group of genetically determined conditions and consider the implications for the broad group of motor neuron diseases in general.
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Affiliation(s)
- Paul A James
- Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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286
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Irobi J, Dierick I, Jordanova A, Claeys KG, De Jonghe P, Timmerman V. Unraveling the genetics of distal hereditary motor neuronopathies. Neuromolecular Med 2006; 8:131-46. [PMID: 16775372 DOI: 10.1385/nmm:8:1-2:131] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 02/02/2023]
Abstract
The hereditary motor neuronopathies (HMN [MIM 158590]) are a heterogeneous group of disorders characterized by an exclusive involvement of the motor part of the peripheral nervous system. They are usually subdivided in proximal HMN, i.e., the classical spinal muscular atrophy syndromes and distal hereditary motor neuronopathies (distal HMN) that clinically resemble Charcot-Marie-Tooth syndromes. In this review, we concentrate on distal HMN. The distal HMN are clinically and genetically heterogeneous and were initially subdivided in seven subtypes according to mode of inheritance, age at onset, and clinical evolution. Recent studies have shown that these subtypes are still heterogeneous at the molecular genetic level and novel clinical and genetic entities have been delineated. Since the introduction of positional cloning, 13 chromosomal loci and seven disease-associated genes have been identified for autosomal-dominant, autosomal-recessive, and X-linked recessive distal HMN. Most of the genes involved encode protein with housekeeping functions, such as RNA processing, translation synthesis, stress response, apoptosis, and others code for proteins involved in retrograde survival. Motor neurons of the anterior horn of the spinal cord seems to be vulnerable to defects in these housekeeping proteins, likely because their large axons have higher metabolic requirements for maintenance, transport over long distances and precise connectivity. Understanding the molecular pathomechanisms for mutations in these genes that are ubiquitous expressed will help unravel the neuronal mechanisms that underlie motor neuropathies leading to denervation of distal limb muscles, and might generate new insights for future therapeutic strategies.
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Affiliation(s)
- Joy Irobi
- Peripheral Neuropathy Group, Department of Molecular Genetics, Flanders Interuniversity Institute for Biotechnology, University of Antwerp, Antwerpen, Belgium
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287
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Berger P, Niemann A, Suter U. Schwann cells and the pathogenesis of inherited motor and sensory neuropathies (Charcot-Marie-Tooth disease). Glia 2006; 54:243-57. [PMID: 16856148 DOI: 10.1002/glia.20386] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Over the last 15 years, a number of mutations in a variety of genes have been identified that lead to inherited motor and sensory neuropathies (HMSN), also called Charcot-Marie-Tooth disease (CMT). In this review we will focus on the molecular and cellular mechanisms that cause the Schwann cell pathologies observed in dysmyelinating and demyelinating forms of CMT. In most instances, the underlying gene defects alter primarily myelinating Schwann cells followed by secondary axonal degeneration. The first set of proteins affected by disease-causing mutations includes the myelin components PMP22, P0/MPZ, Cx32/GJB1, and periaxin. A second group contains the regulators of myelin gene transcription EGR2/Krox20 and SOX10. A third group is composed of intracellular Schwann cells proteins that are likely to be involved in the synthesis, transport and degradation of myelin components. These include the myotubularin-related lipid phosphatase MTMR2 and its regulatory binding partner MTMR13/SBF2, SIMPLE, and potentially also dynamin 2. Mutations affecting the mitochondrial fission factor GDAP1 may indicate an important contribution of mitochondria in myelination or myelin maintenance, whereas the functions of other identified genes, including NDRG1, KIAA1985, and the tyrosyl-tRNA synthase YARS, are not yet clear. Mutations in GDAP1, YARS, and the pleckstrin homology domain of dynamin 2 lead to an intermediate form of CMT that is characterized by moderately reduced nerve conduction velocity consistent with minor myelin deficits. Whether these phenotypes originate in Schwann cells or in neurons, or whether both cell types are directly affected, remains a challenging question. However, based on the advances in systematic gene identification in CMT and the analyses of the function and dysfunction of the affected proteins, crucially interconnected pathways in Schwann cells in health and disease have started to emerge. These networks include the control of myelin formation and stability, membrane trafficking, intracellular protein sorting and quality control, and may extend to mitochondrial dynamics and basic protein biosynthesis.
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Affiliation(s)
- Philipp Berger
- Institute of Cell Biology, Department of Biology, ETH Zürich, Zürich, Switzerland
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