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Sharma G, Paganin M, Lauria F, Perenthaler E, Viero G. The SMN-ribosome interplay: a new opportunity for Spinal Muscular Atrophy therapies. Biochem Soc Trans 2024; 52:465-479. [PMID: 38391004 PMCID: PMC10903476 DOI: 10.1042/bst20231116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 02/12/2024] [Accepted: 02/13/2024] [Indexed: 02/24/2024]
Abstract
The underlying cause of Spinal Muscular Atrophy (SMA) is in the reduction of survival motor neuron (SMN) protein levels due to mutations in the SMN1 gene. The specific effects of SMN protein loss and the resulting pathological alterations are not fully understood. Given the crucial roles of the SMN protein in snRNP biogenesis and its interactions with ribosomes and translation-related proteins and mRNAs, a decrease in SMN levels below a specific threshold in SMA is expected to affect translational control of gene expression. This review covers both direct and indirect SMN interactions across various translation-related cellular compartments and processes, spanning from ribosome biogenesis to local translation and beyond. Additionally, it aims to outline deficiencies and alterations in translation observed in SMA models and patients, while also discussing the implications of the relationship between SMN protein and the translation machinery within the context of current and future therapies.
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2
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Staněk D. Coilin and Cajal bodies. Nucleus 2023; 14:2256036. [PMID: 37682044 PMCID: PMC10494742 DOI: 10.1080/19491034.2023.2256036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 08/24/2023] [Accepted: 08/28/2023] [Indexed: 09/09/2023] Open
Abstract
The nucleus of higher eukaryotes contains a number of structures that concentrate specific biomolecules and play distinct roles in nuclear metabolism. In recent years, the molecular mechanisms controlling their formation have been intensively studied. In this brief review, I focus on coilin and Cajal bodies. Coilin is a key scaffolding protein of Cajal bodies that is evolutionarily conserved in metazoans. Cajal bodies are thought to be one of the archetypal nuclear structures involved in the metabolism of several short non-coding nuclear RNAs. Yet surprisingly little is known about the structure and function of coilin, and a comprehensive model to explain the origin of Cajal bodies is also lacking. Here, I summarize recent results on Cajal bodies and coilin and discuss them in the context of the last three decades of research in this field.
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Affiliation(s)
- David Staněk
- Laboratory of RNA Biology, Institute of Molecular Genetics, Czech Academy of Sciences, Prague, Czech Republic
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3
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Lazo PA, Morejón-García P. VRK1 variants at the cross road of Cajal body neuropathogenic mechanisms in distal neuropathies and motor neuron diseases. Neurobiol Dis 2023; 183:106172. [PMID: 37257665 DOI: 10.1016/j.nbd.2023.106172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 05/09/2023] [Accepted: 05/24/2023] [Indexed: 06/02/2023] Open
Abstract
Distal hereditary neuropathies and neuro motor diseases are complex neurological phenotypes associated with pathogenic variants in a large number of genes, but in some the origin is unknown. Recently, rare pathogenic variants of the human VRK1 gene have been associated with these neurological phenotypes. All VRK1 pathogenic variants are recessive, and their clinical presentation occurs in either homozygous or compound heterozygous patients. The pathogenic VRK1 gene pathogenic variants are located in three clusters within the protein sequence. The main, and initial, shared clinical phenotype among VRK1 pathogenic variants is a distal progressive loss of motor and/or sensory function, which includes diseases such as spinal muscular atrophy, Charcot-Marie-Tooth, amyotrophic lateral sclerosis and hereditary spastic paraplegia. In most cases, symptoms start early in infancy, or in utero, and are slowly progressive. Additional neurological symptoms vary among non-related patients, probably because of their different VRK1 variants and their genetic background. The underlying common pathogenic mechanism, by its functional impairment, is a likely consequence of the roles that the VRK1 protein plays in the regulation on the stability and assembly of Cajal bodies, which affect RNA maturation and processing, neuronal migration of RNPs along axons, and DNA-damage responses. Alterations of these processes are associated with several neuro sensory or motor syndromes. The clinical heterogeneity of the neurological phenotypes associated with VRK1 is a likely consequence of the protein complexes in which VRK1 is integrated, which include several proteins known to be associated with Cajal bodies and DNA damage responses. Several hereditary distal neurological diseases are a consequence of pathogenic variants in genes that alter these cellular functions. We conclude that VRK1-related distal hereditary neuropathies and motor neuron diseases represent a novel subgroup of Cajal body related neurological syndromes.
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Affiliation(s)
- Pedro A Lazo
- Molecular Mechanisms of Cancer Program, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas (CSIC) - Universidad de Salamanca, Salamanca, Spain; Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain.
| | - Patricia Morejón-García
- Molecular Mechanisms of Cancer Program, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas (CSIC) - Universidad de Salamanca, Salamanca, Spain; Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain.
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4
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Li W, Jiang C, Zhang E. Advances in the phase separation-organized membraneless organelles in cells: a narrative review. Transl Cancer Res 2022; 10:4929-4946. [PMID: 35116344 PMCID: PMC8797891 DOI: 10.21037/tcr-21-1111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 10/29/2021] [Indexed: 11/26/2022]
Abstract
Membraneless organelles (MLOs) are micro-compartments that lack delimiting membranes, concentrating several macro-molecules with a high local concentration in eukaryotic cells. Recent studies have shown that MLOs have pivotal roles in multiple biological processes, including gene transcription, RNA metabolism, translation, protein modification, and signal transduction. These biological processes in cells have essential functions in many diseases, such as cancer, neurodegenerative diseases, and virus-related diseases. The liquid-liquid phase separation (LLPS) microenvironment within cells is thought to be the driving force for initiating the formation of micro-compartments with a liquid-like property, becoming an important organizing principle for MLOs to mediate organism responses. In this review, we comprehensively elucidated the formation of these MLOs and the relationship between biological functions and associated diseases. The mechanisms underlying the influence of protein concentration and valency on phase separation in cells are also discussed. MLOs undergoing the LLPS process have diverse functions, including stimulation of some adaptive and reversible responses to alter the transcriptional or translational processes, regulation of the concentrations of biomolecules in living cells, and maintenance of cell morphogenesis. Finally, we highlight that the development of this field could pave the way for developing novel therapeutic strategies for the treatment of LLPS-related diseases based on the understanding of phase separation in the coming years.
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Affiliation(s)
- Weihan Li
- Department of Immunology, School of Medicine, Nantong University, Nantong, China
| | - Chenwei Jiang
- Department of Immunology, School of Medicine, Nantong University, Nantong, China
| | - Erhao Zhang
- Department of Immunology, School of Medicine, Nantong University, Nantong, China.,Laboratory of Medical Science, School of Medicine, Nantong University, Nantong, China
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5
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Trimethylguanosine synthase 1 is a novel regulator of pancreatic beta-cell mass and function. J Biol Chem 2022; 298:101592. [PMID: 35041827 PMCID: PMC8861161 DOI: 10.1016/j.jbc.2022.101592] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 01/06/2022] [Accepted: 01/08/2022] [Indexed: 01/23/2023] Open
Abstract
Type 2 diabetes is a metabolic disorder associated with abnormal glucose homeostasis and is characterized by intrinsic defects in β-cell function and mass. Trimethylguanosine synthase 1 (TGS1) is an evolutionarily conserved enzyme that methylates small nuclear and nucleolar RNAs and that is involved in pre-mRNA splicing, transcription, and ribosome production. However, the role of TGS1 in β-cells and glucose homeostasis had not been explored. Here, we show that TGS1 is upregulated by insulin and upregulated in islets of Langerhans from mice exposed to a high-fat diet and in human β-cells from type 2 diabetes donors. Using mice with conditional (βTGS1KO) and inducible (MIP-CreERT-TGS1KO) TGS1 deletion, we determined that TGS1 regulates β-cell mass and function. Using unbiased approaches, we identified a link between TGS1 and endoplasmic reticulum stress and cell cycle arrest, as well as and how TGS1 regulates β-cell apoptosis. We also found that deletion of TGS1 results in an increase in the unfolded protein response by increasing XBP-1, ATF-4, and the phosphorylation of eIF2α, in addition to promoting several changes in cell cycle inhibitors and activators such as p27 and Cyclin D2. This study establishes TGS1 as a key player regulating β-cell mass and function. We propose that these observations can be used as a stepping-stone for the design of novel strategies focused on TGS1 as a therapeutic target for the treatment of diabetes.
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Bergfort A, Hilal T, Kuropka B, Ilik İA, Weber G, Aktaş T, Freund C, Wahl MC. OUP accepted manuscript. Nucleic Acids Res 2022; 50:2938-2958. [PMID: 35188580 PMCID: PMC8934646 DOI: 10.1093/nar/gkac087] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 01/21/2022] [Accepted: 01/26/2022] [Indexed: 11/16/2022] Open
Abstract
Biogenesis of spliceosomal small nuclear ribonucleoproteins (snRNPs) and their recycling after splicing require numerous assembly/recycling factors whose modes of action are often poorly understood. The intrinsically disordered TSSC4 protein has been identified as a nuclear-localized U5 snRNP and U4/U6-U5 tri-snRNP assembly/recycling factor, but how TSSC4’s intrinsic disorder supports TSSC4 functions remains unknown. Using diverse interaction assays and cryogenic electron microscopy-based structural analysis, we show that TSSC4 employs four conserved, non-contiguous regions to bind the PRPF8 Jab1/MPN domain and the SNRNP200 helicase at functionally important sites. It thereby inhibits SNRNP200 helicase activity, spatially aligns the proteins, coordinates formation of a U5 sub-module and transiently blocks premature interaction of SNRNP200 with at least three other spliceosomal factors. Guided by the structure, we designed a TSSC4 variant that lacks stable binding to the PRPF8 Jab1/MPN domain or SNRNP200 in vitro. Comparative immunoprecipitation/mass spectrometry from HEK293 nuclear extract revealed distinct interaction profiles of wild type TSSC4 and the variant deficient in PRPF8/SNRNP200 binding with snRNP proteins, other spliceosomal proteins as well as snRNP assembly/recycling factors and chaperones. Our findings elucidate molecular strategies employed by an intrinsically disordered protein to promote snRNP assembly, and suggest multiple TSSC4-dependent stages during snRNP assembly/recycling.
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Affiliation(s)
- Alexandra Bergfort
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of Structural Biochemistry, Takustr. 6, D-14195 Berlin, Germany
| | - Tarek Hilal
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of Structural Biochemistry, Takustr. 6, D-14195 Berlin, Germany
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Research Center of Electron Microscopy, Fabeckstr. 36a, 14195 Berlin, Germany
| | - Benno Kuropka
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of Protein Biochemistry, Thielallee 63, D-14195, Berlin, Germany
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Core Facility BioSupraMol, Thielallee 63, D-14195, Berlin, Germany
| | - İbrahim Avşar Ilik
- Max Planck Institute for Molecular Genetics, Ihnestr. 63, D-14195 Berlin, Germany
| | - Gert Weber
- Helmholtz-Zentrum Berlin für Materialien und Energie, Macromolecular Crystallography, Albert-Einstein-Str. 15, D-12489 Berlin, Germany
| | - Tuğçe Aktaş
- Max Planck Institute for Molecular Genetics, Ihnestr. 63, D-14195 Berlin, Germany
| | - Christian Freund
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of Protein Biochemistry, Thielallee 63, D-14195, Berlin, Germany
| | - Markus C Wahl
- To whom correspondence should be addressed. Tel: +49 30 838 53456; Fax: +49 30 8384 53456;
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Courchaine EM, Barentine AES, Straube K, Lee DR, Bewersdorf J, Neugebauer KM. DMA-tudor interaction modules control the specificity of in vivo condensates. Cell 2021; 184:3612-3625.e17. [PMID: 34115980 DOI: 10.1016/j.cell.2021.05.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 12/21/2020] [Accepted: 05/07/2021] [Indexed: 12/31/2022]
Abstract
Biomolecular condensation is a widespread mechanism of cellular compartmentalization. Because the "survival of motor neuron protein" (SMN) is implicated in the formation of three different membraneless organelles (MLOs), we hypothesized that SMN promotes condensation. Unexpectedly, we found that SMN's globular tudor domain was sufficient for dimerization-induced condensation in vivo, whereas its two intrinsically disordered regions (IDRs) were not. Binding to dimethylarginine (DMA) modified protein ligands was required for condensate formation by the tudor domains in SMN and at least seven other fly and human proteins. Remarkably, asymmetric versus symmetric DMA determined whether two distinct nuclear MLOs-gems and Cajal bodies-were separate or "docked" to one another. This substructure depended on the presence of either asymmetric or symmetric DMA as visualized with sub-diffraction microscopy. Thus, DMA-tudor interaction modules-combinations of tudor domains bound to their DMA ligand(s)-represent versatile yet specific regulators of MLO assembly, composition, and morphology.
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Affiliation(s)
- Edward M Courchaine
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Andrew E S Barentine
- Cell Biology, Yale University, New Haven, CT 06520, USA; Biomedical Engineering, Yale University, New Haven, CT 06520, USA
| | - Korinna Straube
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | | | - Joerg Bewersdorf
- Cell Biology, Yale University, New Haven, CT 06520, USA; Biomedical Engineering, Yale University, New Haven, CT 06520, USA
| | - Karla M Neugebauer
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA; Cell Biology, Yale University, New Haven, CT 06520, USA.
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Marcos AT, Martín‐Doncel E, Morejón‐García P, Marcos‐Alcalde I, Gómez‐Puertas P, Segura‐Puimedon M, Armengol L, Navarro‐Pando JM, Lazo PA. VRK1 (Y213H) homozygous mutant impairs Cajal bodies in a hereditary case of distal motor neuropathy. Ann Clin Transl Neurol 2020; 7:808-818. [PMID: 32365420 PMCID: PMC7261760 DOI: 10.1002/acn3.51050] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Revised: 03/27/2020] [Accepted: 03/31/2020] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Distal motor neuropathies with a genetic origin have a heterogeneous clinical presentation with overlapping features affecting distal nerves and including spinal muscular atrophies and amyotrophic lateral sclerosis. This indicates that their genetic background is heterogeneous. PATIENT AND METHODS In this work, we have identified and characterized the genetic and molecular base of a patient with a distal sensorimotor neuropathy of unknown origin. For this study, we performed whole-exome sequencing, molecular modelling, cloning and expression of mutant gene, and biochemical and cell biology analysis of the mutant protein. RESULTS A novel homozygous recessive mutation in the human VRK1 gene, coding for a chromatin kinase, causing a substitution (c.637T > C; p.Tyr213His) in exon 8, was detected in a patient presenting since childhood a progressive distal sensorimotor neuropathy and spinal muscular atrophy syndrome, with normal intellectual development. Molecular modelling predicted this mutant VRK1 has altered the kinase activation loop by disrupting its interaction with the C-terminal regulatory region. The p.Y213H mutant protein has a reduced kinase activity with different substrates, including histones H3 and H2AX, proteins involved in DNA damage responses, such as p53 and 53BP1, and coilin, the scaffold for Cajal bodies. The mutant VRK1(Y213H) protein is unable to rescue the formation of Cajal bodies assembled on coilin, in the absence of wild-type VRK1. CONCLUSION The VRK1(Y213H) mutant protein alters the activation loop, impairs the kinase activity of VRK1 causing a functional insufficiency that impairs the formation of Cajal bodies assembled on coilin, a protein that regulates SMN1 and Cajal body formation.
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Affiliation(s)
- Ana T. Marcos
- Unidad de GenéticaInstituto para el Estudio de la Biología de la Reproducción Humana (INEBIR)SevillaSpain
| | - Elena Martín‐Doncel
- Molecular Mechanisms of Cancer ProgramInstituto de Biología Molecular y Celular del CáncerConsejo Superior de Investigaciones Científicas (CSIC)Universidad de SalamancaSalamancaSpain
- Instituto de Investigación Biomédica de Salamanca (IBSAL)Hospital Universitario de SalamancaSalamancaSpain
| | - Patricia Morejón‐García
- Molecular Mechanisms of Cancer ProgramInstituto de Biología Molecular y Celular del CáncerConsejo Superior de Investigaciones Científicas (CSIC)Universidad de SalamancaSalamancaSpain
- Instituto de Investigación Biomédica de Salamanca (IBSAL)Hospital Universitario de SalamancaSalamancaSpain
| | - Iñigo Marcos‐Alcalde
- Molecular Modelling GroupCentro de Biología Molecular “Severo Ochoa”CSIC‐Universidad Autónoma de Madrid, CantoblancoMadridSpain
- School of Experimental SciencesBiosciences Research InstituteUniversidad Francisco de VitoriaPozuelo de Alarcón, MadridSpain
| | - Paulino Gómez‐Puertas
- Molecular Modelling GroupCentro de Biología Molecular “Severo Ochoa”CSIC‐Universidad Autónoma de Madrid, CantoblancoMadridSpain
| | - María Segura‐Puimedon
- Quantitative Genomic Medicine Laboratories, qGenomicsEspluges de LlobregatBarcelonaSpain
| | - Lluis Armengol
- Quantitative Genomic Medicine Laboratories, qGenomicsEspluges de LlobregatBarcelonaSpain
| | - José M. Navarro‐Pando
- Unidad de GenéticaInstituto para el Estudio de la Biología de la Reproducción Humana (INEBIR)SevillaSpain
- Cátedra de Reproducción y Genética HumanaFacultad de Ciencias de la SaludUniversidad Europea del AtlánticoSantanderSpain
- Fundación Universitaria Iberoamericana (FUNIBER)BarcelonaSpain
| | - Pedro A. Lazo
- Molecular Mechanisms of Cancer ProgramInstituto de Biología Molecular y Celular del CáncerConsejo Superior de Investigaciones Científicas (CSIC)Universidad de SalamancaSalamancaSpain
- Instituto de Investigación Biomédica de Salamanca (IBSAL)Hospital Universitario de SalamancaSalamancaSpain
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Moreno-Castro C, Prieto-Sánchez S, Sánchez-Hernández N, Hernández-Munain C, Suñé C. Role for the splicing factor TCERG1 in Cajal body integrity and snRNP assembly. J Cell Sci 2019; 132:jcs.232728. [PMID: 31636114 DOI: 10.1242/jcs.232728] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 10/11/2019] [Indexed: 12/29/2022] Open
Abstract
Cajal bodies are nuclear organelles involved in the nuclear phase of small nuclear ribonucleoprotein (snRNP) biogenesis. In this study, we identified the splicing factor TCERG1 as a coilin-associated factor that is essential for Cajal body integrity. Knockdown of TCERG1 disrupts the localization of the components of Cajal bodies, including coilin and NOLC1, with coilin being dispersed in the nucleoplasm into numerous small foci, without affecting speckles, gems or the histone locus body. Furthermore, the depletion of TCERG1 affects the recruitment of Sm proteins to uridine-rich small nuclear RNAs (snRNAs) to form the mature core snRNP. Taken together, the results of this study suggest that TCERG1 plays an important role in Cajal body formation and snRNP biogenesis.
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Affiliation(s)
- Cristina Moreno-Castro
- Department of Molecular Biology, Institute of Parasitology and Biomedicine "López-Neyra" (IPBLN-CSIC), PTS, 18016 Granada, Spain
| | - Silvia Prieto-Sánchez
- Department of Molecular Biology, Institute of Parasitology and Biomedicine "López-Neyra" (IPBLN-CSIC), PTS, 18016 Granada, Spain
| | - Noemí Sánchez-Hernández
- Department of Molecular Biology, Institute of Parasitology and Biomedicine "López-Neyra" (IPBLN-CSIC), PTS, 18016 Granada, Spain
| | - Cristina Hernández-Munain
- Department of Cell Biology and Immunology, Institute of Parasitology and Biomedicine "López-Neyra" (IPBLN-CSIC), PTS, 18016 Granada, Spain
| | - Carlos Suñé
- Department of Molecular Biology, Institute of Parasitology and Biomedicine "López-Neyra" (IPBLN-CSIC), PTS, 18016 Granada, Spain
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10
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Kobayashi M, Zochodne DW. Diabetic neuropathy and the sensory neuron: New aspects of pathogenesis and their treatment implications. J Diabetes Investig 2018; 9:1239-1254. [PMID: 29533535 PMCID: PMC6215951 DOI: 10.1111/jdi.12833] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 02/20/2018] [Accepted: 03/03/2018] [Indexed: 12/17/2022] Open
Abstract
Diabetic polyneuropathy (DPN) continues to be generally considered as a "microvascular" complication of diabetes mellitus alongside nephropathy and retinopathy. The microvascular hypothesis, however, might be tempered by the concept that diabetes directly targets dorsal root ganglion sensory neurons. This neuron-specific concept, supported by accumulating evidence, might account for important features of DPN, such as its early sensory neuron degeneration. Diabetic sensory neurons develop neuronal atrophy alongside a series of messenger ribonucleic acid (RNA) changes related to declines in structural proteins, increases in heat shock protein, increases in the receptor for advanced glycation end-products, declines in growth factor signaling and other changes. Insulin is recognized as a potent neurotrophic factor, and insulin ligation enhances neurite outgrowth through activation of the phosphoinositide 3-kinase-protein kinase B pathway within sensory neurons and attenuates phenotypic features of experimental DPN. Several interventions, including glucagon-like peptide-1 agonism, and phosphatase and tensin homolog inhibition to activate growth signals in sensory neurons, or heat shock protein overexpression, prevent or reverse neuropathic abnormalities in experimental DPN. Diabetic sensory neurons show a unique pattern of microRNA alterations, a key element of messenger RNA silencing. For example, let-7i is widely expressed in sensory neurons, supports their growth and is depleted in experimental DPN; its replenishment improves features of DPN models. Finally, impairment of pre-messenger RNA splicing in diabetic sensory neurons including abnormal nuclear RNA metabolism and structure with loss of survival motor neuron protein, a neuron survival molecule, and overexpression of CWC22, a splicing factor, offer further novel insights. The present review addresses these new aspects of DPN sensory neurodegeneration.
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Affiliation(s)
- Masaki Kobayashi
- Department of Neurology and Neurological ScienceGraduate School of MedicineTokyo Medical and Dental UniversityTokyoJapan
- Department of NeurologyYokufukai Geriatric HospitalTokyoJapan
| | - Douglas W Zochodne
- Division of Neurology and Department of MedicineNeuroscience and Mental Health InstituteFaculty of Medicine and DentistryUniversity of AlbertaEdmontonAlbertaCanada
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11
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Kobayashi M, Chandrasekhar A, Cheng C, Martinez JA, Ng H, de la Hoz C, Zochodne DW. Diabetic polyneuropathy, sensory neurons, nuclear structure and spliceosome alterations: a role for CWC22. Dis Model Mech 2017; 10:215-224. [PMID: 28250049 PMCID: PMC5374325 DOI: 10.1242/dmm.028225] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 12/23/2016] [Indexed: 12/31/2022] Open
Abstract
Unique deficits in the function of adult sensory neurons as part of their early neurodegeneration might account for progressive polyneuropathy during chronic diabetes mellitus. Here, we provide structural and functional evidence for aberrant pre-mRNA splicing in a chronic type 1 model of experimental diabetic polyneuropathy (DPN). Cajal bodies (CBs), unique nuclear substructures involved in RNA splicing, increased in number in diabetic sensory neurons, but their expected colocalization with survival motor neuron (SMN) proteins was reduced - a mislocalization described in motor neurons of spinal muscular atrophy. Small nuclear ribonucleoprotein particles (snRNPs), also participants in the spliceosome, had abnormal multiple nuclear foci unassociated with CBs, and their associated snRNAs were reduced. CWC22, a key spliceosome protein, was aberrantly upregulated in diabetic dorsal root ganglia (DRG), and impaired neuronal function. CWC22 attenuated sensory neuron plasticity, with knockdown in vitro enhancing their neurite outgrowth. Further, axonal delivery of CWC22 siRNA unilaterally to locally knock down the aberrant protein in diabetic nerves improved aspects of sensory function in diabetic mice. Collectively, our findings identify subtle but significant alterations in spliceosome structure and function, including dysregulated CBs and CWC22 overexpression, in diabetic sensory neurons that offer new ideas regarding diabetic sensory neurodegeneration in polyneuropathy.
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Affiliation(s)
- Masaki Kobayashi
- Division of Neurology and Department of Medicine, Faculty of Medicine and Dentistry, and the Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada, T6G 2G3
| | - Ambika Chandrasekhar
- Division of Neurology and Department of Medicine, Faculty of Medicine and Dentistry, and the Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada, T6G 2G3
| | - Chu Cheng
- Hotchkiss Brain Institute and Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Canada, T2N 4N1
| | - Jose A Martinez
- Hotchkiss Brain Institute and Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Canada, T2N 4N1
| | - Hilarie Ng
- Hotchkiss Brain Institute and Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Canada, T2N 4N1
| | - Cristiane de la Hoz
- Hotchkiss Brain Institute and Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Canada, T2N 4N1
| | - Douglas W Zochodne
- Division of Neurology and Department of Medicine, Faculty of Medicine and Dentistry, and the Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada, T6G 2G3 .,Hotchkiss Brain Institute and Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Canada, T2N 4N1
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12
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Gruss OJ, Meduri R, Schilling M, Fischer U. UsnRNP biogenesis: mechanisms and regulation. Chromosoma 2017; 126:577-593. [PMID: 28766049 DOI: 10.1007/s00412-017-0637-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Revised: 07/14/2017] [Accepted: 07/14/2017] [Indexed: 12/24/2022]
Abstract
Macromolecular complexes composed of proteins or proteins and nucleic acids rather than individual macromolecules mediate many cellular activities. Maintenance of these activities is essential for cell viability and requires the coordinated production of the individual complex components as well as their faithful incorporation into functional entities. Failure of complex assembly may have fatal consequences and can cause severe diseases. While many macromolecular complexes can form spontaneously in vitro, they often require aid from assembly factors including assembly chaperones in the crowded cellular environment. The assembly of RNA protein complexes implicated in the maturation of pre-mRNAs (termed UsnRNPs) has proven to be a paradigm to understand the action of assembly factors and chaperones. UsnRNPs are assembled by factors united in protein arginine methyltransferase 5 (PRMT5)- and survival motor neuron (SMN)-complexes, which act sequentially in the UsnRNP production line. While the PRMT5-complex pre-arranges specific sets of proteins into stable intermediates, the SMN complex displaces assembly factors from these intermediates and unites them with UsnRNA to form the assembled RNP. Despite advanced mechanistic understanding of UsnRNP assembly, our knowledge of regulatory features of this essential and ubiquitous cellular function remains remarkably incomplete. One may argue that the process operates as a default biosynthesis pathway and does not require sophisticated regulatory cues. Simple theoretical considerations and a number of experimental data, however, indicate that regulation of UsnRNP assembly most likely happens at multiple levels. This review will not only summarize how individual components of this assembly line act mechanistically but also why, how, and when the UsnRNP workflow might be regulated by means of posttranslational modification in response to cellular signaling cues.
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Affiliation(s)
- Oliver J Gruss
- Department of Genetics, Rheinische Friedrich-Wilhelms-Universität Bonn, Karlrobert-Kreiten-Str. 13, 53115, Bonn, Germany.
| | - Rajyalakshmi Meduri
- Department of Biochemistry, University of Würzburg, Biozentrum, Am Hubland, D-97074, Würzburg, Germany
| | - Maximilian Schilling
- Department of Genetics, Rheinische Friedrich-Wilhelms-Universität Bonn, Karlrobert-Kreiten-Str. 13, 53115, Bonn, Germany
| | - Utz Fischer
- Department of Biochemistry, University of Würzburg, Biozentrum, Am Hubland, D-97074, Würzburg, Germany.
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13
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Raimer AC, Gray KM, Matera AG. SMN - A chaperone for nuclear RNP social occasions? RNA Biol 2017; 14:701-711. [PMID: 27648855 PMCID: PMC5519234 DOI: 10.1080/15476286.2016.1236168] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 09/01/2016] [Accepted: 09/09/2016] [Indexed: 12/24/2022] Open
Abstract
Survival Motor Neuron (SMN) protein localizes to both the nucleus and the cytoplasm. Cytoplasmic SMN is diffusely localized in large oligomeric complexes with core member proteins, called Gemins. Biochemical and cell biological studies have demonstrated that the SMN complex is required for the cytoplasmic assembly and nuclear transport of Sm-class ribonucleoproteins (RNPs). Nuclear SMN accumulates with spliceosomal small nuclear (sn)RNPs in Cajal bodies, sub-domains involved in multiple facets of snRNP maturation. Thus, the SMN complex forms stable associations with both nuclear and cytoplasmic snRNPs, and plays a critical role in their biogenesis. In this review, we focus on potential functions of the nuclear SMN complex, with particular emphasis on its role within the Cajal body.
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Affiliation(s)
- Amanda C. Raimer
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Integrative Program for Biological and Genome Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Kelsey M. Gray
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Integrative Program for Biological and Genome Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - A. Gregory Matera
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Integrative Program for Biological and Genome Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Department of Genetics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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14
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Akpınar M, Lesche M, Fanourgakis G, Fu J, Anasstasiadis K, Dahl A, Jessberger R. TDRD6 mediates early steps of spliceosome maturation in primary spermatocytes. PLoS Genet 2017; 13:e1006660. [PMID: 28263986 PMCID: PMC5358835 DOI: 10.1371/journal.pgen.1006660] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 03/20/2017] [Accepted: 02/26/2017] [Indexed: 12/24/2022] Open
Abstract
Tudor containing protein 6 (TDRD6) is a male germ line-specific protein essential for chromatoid body (ChB) structure, elongated spermatid development and male fertility. Here we show that in meiotic prophase I spermatocytes TDRD6 interacts with the key protein arginine methyl transferase PRMT5, which supports splicing. TDRD6 also associates with spliceosomal core protein SmB in the absence of RNA and in an arginine methylation dependent manner. In Tdrd6-/- diplotene spermatocytes PRMT5 association with SmB and arginine dimethylation of SmB are much reduced. TDRD6 deficiency impairs the assembly of spliceosomes, which feature 3.5-fold increased levels of U5 snRNPs. In the nucleus, these deficiencies in spliceosome maturation correlate with decreased numbers of SMN-positive bodies and Cajal bodies involved in nuclear snRNP maturation. Transcriptome analysis of TDRD6-deficient diplotene spermatocytes revealed high numbers of splicing defects such as aberrant usage of intron and exons as well as aberrant representation of splice junctions. Together, this study demonstrates a novel function of TDRD6 in spliceosome maturation and mRNA splicing in prophase I spermatocytes.
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Affiliation(s)
- Müge Akpınar
- Institute of Physiological Chemistry, Medical Faculty Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Mathias Lesche
- Deep Sequencing Group SFB 655, Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Grigorios Fanourgakis
- Institute of Physiological Chemistry, Medical Faculty Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Jun Fu
- Stem Cell Engineering, Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | | | - Andreas Dahl
- Deep Sequencing Group SFB 655, Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Rolf Jessberger
- Institute of Physiological Chemistry, Medical Faculty Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
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15
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Trinkle-Mulcahy L, Sleeman JE. The Cajal body and the nucleolus: "In a relationship" or "It's complicated"? RNA Biol 2016; 14:739-751. [PMID: 27661468 DOI: 10.1080/15476286.2016.1236169] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
From their initial identification as 'nucleolar accessory bodies' more than a century ago, the relationship between Cajal bodies and nucleoli has been a subject of interest and controversy. In this review, we seek to place recent developments in the understanding of the physical and functional relationships between the 2 structures in the context of historical observations. Biophysical models of nuclear body formation, the molecular nature of CB/nucleolus interactions and the increasing list of joint roles for CBs and nucleoli, predominantly in assembling ribonucleoprotein (RNP) complexes, are discussed.
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Affiliation(s)
- Laura Trinkle-Mulcahy
- a Department of Cellular and Molecular Medicine , Ottawa Institute of Systems Biology, University of Ottawa , Ottawa , ON , Canada
| | - Judith E Sleeman
- b BSRC Complex, School of Biology, University of St Andrews , UK
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16
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Fuller HR, Gillingwater TH, Wishart TM. Commonality amid diversity: Multi-study proteomic identification of conserved disease mechanisms in spinal muscular atrophy. Neuromuscul Disord 2016; 26:560-9. [PMID: 27460344 DOI: 10.1016/j.nmd.2016.06.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 06/03/2016] [Indexed: 01/09/2023]
Abstract
The neuromuscular disease spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting from low levels of full-length survival motor neuron (SMN) protein. Despite having a good understanding of the underlying genetics of SMA, the molecular pathways downstream of SMN that regulate disease pathogenesis remain unclear. The identification of molecular perturbations downstream of SMN is required in order to fully understand the fundamental biological role(s) for SMN in cells and tissues of the body, as well as to develop a range of therapeutic targets for developing novel treatments for SMA. Recent developments in proteomic screening technologies have facilitated proteome-wide investigations of a range of SMA models and tissues, generating novel insights into disease mechanisms by highlighting conserved changes in a range of molecular pathways. Comparative analysis of distinct proteomic datasets reveals conserved changes in pathways converging on GAP43, GAPDH, NCAM, UBA1, LMNA, ANXA2 and COL6A3. Proteomic studies therefore represent a leading tool with which to dissect the molecular mechanisms of disease pathogenesis in SMA, serving to identify potentially attractive targets for the development of novel therapies.
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Affiliation(s)
- Heidi R Fuller
- Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry SY10 7AG, UK; Institute for Science and Technology in Medicine, Keele University, Staffordshire ST5 5BG, UK.
| | - Thomas H Gillingwater
- Centre for Integrative Physiology, University of Edinburgh, UK; Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, UK
| | - Thomas M Wishart
- Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, UK; Division of Neurobiology, The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, UK.
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17
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Abstract
Initially identified as a marker of coiled bodies (now Cajal bodies or CBs), the protein coilin was discovered a quarter of century ago. Coilin is now known to scaffold the CB, but its structure and function are poorly understood. Nearly devoid of predicted structural motifs, coilin has numerous reported molecular interactions that must underlie its role in the formation and function of CBs. In this review, we summarize what we have learned in the past 25 years about coilin's structure, post-transcriptional modifications, and interactions with RNA and proteins. We show that genes with homology to human coilin are found in primitive metazoans and comment on differences among model organisms. Coilin's function in Cajal body formation and RNP metabolism will be discussed in the light of these developments.
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Affiliation(s)
- Martin Machyna
- a Department of Molecular Biophysics & Biochemistry ; Yale University ; New Haven , CT USA
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18
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Enwerem II, Wu G, Yu YT, Hebert MD. Cajal body proteins differentially affect the processing of box C/D scaRNPs. PLoS One 2015; 10:e0122348. [PMID: 25875178 PMCID: PMC4395269 DOI: 10.1371/journal.pone.0122348] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 02/13/2015] [Indexed: 11/19/2022] Open
Abstract
Small nuclear ribonucleoproteins (snRNPs), which are required for pre-mRNA splicing, contain extensively modified snRNA. Small Cajal body-specific ribonucleoproteins (scaRNPs) mediate these modifications. It is unknown how the box C/D class of scaRNPs localizes to Cajal Bodies (CBs). The processing of box C/D scaRNA is also unclear. Here, we explore the processing of box C/D scaRNA 2 and 9 by coilin. We also broaden our investigation to include WRAP53 and SMN, which accumulate in CBs, play a role in RNP biogenesis and associate with coilin. These studies demonstrate that the processing of an ectopically expressed scaRNA2 is altered upon the reduction of coilin, WRAP53 or SMN, but the extent and direction of this change varies depending on the protein reduced. We also show that box C/D scaRNP activity is reduced in a cell line derived from coilin knockout mice. Collectively, the findings presented here further implicate coilin as being a direct participant in the formation of box C/D scaRNPs, and demonstrate that WRAP53 and SMN may also play a role, but the activity of these proteins is divergent to coilin.
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Affiliation(s)
- Isioma I. Enwerem
- Department of Biochemistry, The University of Mississippi Medical Center, Jackson, Mississippi 39216–4505, United States of America
| | - Guowei Wu
- Department of Biochemistry and Biophysics, The University of Rochester Medical Center, Rochester, New York 14642, United States of America
| | - Yi Tao Yu
- Department of Biochemistry and Biophysics, The University of Rochester Medical Center, Rochester, New York 14642, United States of America
| | - Michael D. Hebert
- Department of Biochemistry, The University of Mississippi Medical Center, Jackson, Mississippi 39216–4505, United States of America
- * E-mail:
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19
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Stejskalová E, Staněk D. The splicing factor U1-70K interacts with the SMN complex and is required for nuclear gem integrity. J Cell Sci 2014; 127:3909-15. [PMID: 25052091 DOI: 10.1242/jcs.155838] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The nuclear SMN complex localizes to specific structures called nuclear gems. The loss of gems is a cellular marker for several neurodegenerative diseases. Here, we identify that the U1-snRNP-specific protein U1-70K localizes to nuclear gems, and we show that U1-70K is necessary for gem integrity. Furthermore, we show that the interaction between U1-70K and the SMN complex is RNA independent, and we map the SMN complex binding site to the unstructured N-terminal tail of U1-70K. Consistent with these results, the expression of the U1-70K N-terminal tail rescues gem formation. These findings show that U1-70K is an SMN-complex-associating protein, and they suggest a new function for U1-70K in the formation of nuclear gems.
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Affiliation(s)
- Eva Stejskalová
- Department of RNA Biology, Institute of Molecular Genetics AS CR, 142 20 Prague, Czech Republic Faculty of Science, Charles University in Prague, 128 43 Prague, Czech Republic
| | - David Staněk
- Department of RNA Biology, Institute of Molecular Genetics AS CR, 142 20 Prague, Czech Republic
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20
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Abstract
This review summarizes the current understanding of the role of nuclear bodies in regulating gene expression. The compartmentalization of cellular processes, such as ribosome biogenesis, RNA processing, cellular response to stress, transcription, modification and assembly of spliceosomal snRNPs, histone gene synthesis and nuclear RNA retention, has significant implications for gene regulation. These functional nuclear domains include the nucleolus, nuclear speckle, nuclear stress body, transcription factory, Cajal body, Gemini of Cajal body, histone locus body and paraspeckle. We herein review the roles of nuclear bodies in regulating gene expression and their relation to human health and disease.
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Affiliation(s)
| | - Cornelius F. Boerkoel
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-604-875-2157; Fax: +1-604-875-2376
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21
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Cauchi RJ. Gem depletion: amyotrophic lateral sclerosis and spinal muscular atrophy crossover. CNS Neurosci Ther 2014; 20:574-81. [PMID: 24645792 DOI: 10.1111/cns.12242] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2013] [Revised: 01/25/2014] [Accepted: 01/27/2014] [Indexed: 12/22/2022] Open
Abstract
The determining factor of spinal muscular atrophy (SMA), the most common motor neuron degenerative disease of childhood, is the survival motor neuron (SMN) protein. SMN and its Gemin associates form a complex that is indispensible for the biogenesis of small nuclear ribonucleoproteins (snRNPs), which constitute the building blocks of spliceosomes. It is as yet unclear whether a decreased capacity of SMN in snRNP assembly, and, hence, transcriptome abnormalities, account for the specific neuromuscular phenotype in SMA. Across metazoa, the SMN-Gemins complex concentrates in multiple nuclear gems that frequently neighbour or overlap Cajal bodies. The number of gems has long been known to be a faithful indicator of SMN levels, which are linked to SMA severity. Intriguingly, a flurry of recent studies have revealed that depletion of this nuclear structure is also a signature feature of amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disease. This review discusses such a surprising crossover in addition to highlighting the most recent work on the intricate world of spliceosome building, which seems to be at the heart of motor neuron physiology and survival.
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Affiliation(s)
- Ruben J Cauchi
- Department of Physiology and Biochemistry, University of Malta, Msida 2080, Malta
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22
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Li Y, Fong KW, Tang M, Han X, Gong Z, Ma W, Hebert M, Songyang Z, Chen J. Fam118B, a newly identified component of Cajal bodies, is required for Cajal body formation, snRNP biogenesis and cell viability. J Cell Sci 2014; 127:2029-39. [PMID: 24569877 DOI: 10.1242/jcs.143453] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cajal bodies are specialized and dynamic compartments in the nucleus that are involved in the biogenesis of small nuclear ribonucleoproteins (snRNPs). Because of the dynamic and varied roles of Cajal bodies, it is of great interest to identify the components of Cajal bodies to better understand their functions. We performed a genome-wide screen to identify proteins that colocalize with coilin, the marker protein of Cajal bodies. In this study, we identified and characterized Fam118B as a newly discovered component of Cajal bodies. Fam118B is widely expressed in a variety of cell lines derived from various origins. Overexpression of Fam118B changes the canonical morphology of Cajal bodies, whereas depletion of Fam118B disrupts the localization of components of Cajal bodies, including coilin, the survival of motor neuron protein (SMN) and the Sm protein D1 (SmD1, also known as SNRPD1). Moreover, depletion of Fam118B reduces splicing capacity and inhibits cell proliferation. In addition, Fam118B associates with coilin and SMN proteins. Fam118B depletion reduces symmetric dimethylarginine modification of SmD1, which in turn diminishes the binding of SMN to this Sm protein. Taken together, these data indicate that Fam118B, by regulating SmD1 symmetric dimethylarginine modification, plays an important role in Cajal body formation, snRNP biogenesis and cell viability.
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Affiliation(s)
- Yujing Li
- State Key Laboratory for Biocontrol and Key Laboratory of Gene Engineering of Ministry of Education, Sun Yat-Sen University-Baylor College of Medicine Joint Research Center on Biomedical Sciences, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China
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23
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Fong KW, Li Y, Wang W, Ma W, Li K, Qi RZ, Liu D, Songyang Z, Chen J. Whole-genome screening identifies proteins localized to distinct nuclear bodies. ACTA ACUST UNITED AC 2013; 203:149-64. [PMID: 24127217 PMCID: PMC3798253 DOI: 10.1083/jcb.201303145] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The nucleus is a unique organelle that contains essential genetic materials in chromosome territories. The interchromatin space is composed of nuclear subcompartments, which are defined by several distinctive nuclear bodies believed to be factories of DNA or RNA processing and sites of transcriptional and/or posttranscriptional regulation. In this paper, we performed a genome-wide microscopy-based screening for proteins that form nuclear foci and characterized their localizations using markers of known nuclear bodies. In total, we identified 325 proteins localized to distinct nuclear bodies, including nucleoli (148), promyelocytic leukemia nuclear bodies (38), nuclear speckles (27), paraspeckles (24), Cajal bodies (17), Sam68 nuclear bodies (5), Polycomb bodies (2), and uncharacterized nuclear bodies (64). Functional validation revealed several proteins potentially involved in the assembly of Cajal bodies and paraspeckles. Together, these data establish the first atlas of human proteins in different nuclear bodies and provide key information for research on nuclear bodies.
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Affiliation(s)
- Ka-Wing Fong
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030
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24
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Hallais M, Pontvianne F, Andersen PR, Clerici M, Lener D, Benbahouche NEH, Gostan T, Vandermoere F, Robert MC, Cusack S, Verheggen C, Jensen TH, Bertrand E. CBC-ARS2 stimulates 3'-end maturation of multiple RNA families and favors cap-proximal processing. Nat Struct Mol Biol 2013; 20:1358-66. [PMID: 24270878 DOI: 10.1038/nsmb.2720] [Citation(s) in RCA: 124] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Accepted: 10/24/2013] [Indexed: 02/07/2023]
Abstract
The nuclear cap-binding complex (CBC) stimulates multiple steps in several RNA maturation pathways, but how it functions in humans is incompletely understood. For small, capped RNAs such as pre-snRNAs, the CBC recruits PHAX. Here, we identify the CBCAP complex, composed of CBC, ARS2 and PHAX, and show that both CBCAP and CBC-ARS2 complexes can be reconstituted from recombinant proteins. ARS2 stimulates PHAX binding to the CBC and snRNA 3'-end processing, thereby coupling maturation with export. In vivo, CBC and ARS2 bind similar capped noncoding and coding RNAs and stimulate their 3'-end processing. The strongest effects are for cap-proximal polyadenylation sites, and this favors premature transcription termination. ARS2 functions partly through the mRNA 3'-end cleavage factor CLP1, which binds RNA Polymerase II through PCF11. ARS2 is thus a major CBC effector that stimulates functional and cryptic 3'-end processing sites.
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Affiliation(s)
- Marie Hallais
- Equipe labellisée Ligue contre le Cancer, Institut de Génétique Moléculaire de Montpellier-Centre National de la Recherche Scientifique, Montpellier, France
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25
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Sabra M, Texier P, El Maalouf J, Lomonte P. The tudor protein survival motor neuron (SMN) is a chromatin-binding protein that interacts with methylated histone H3 lysine 79. J Cell Sci 2013; 126:3664-77. [DOI: 10.1242/jcs.126003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Spinal muscular atrophy (SMA) is a muscular disease characterized by the death of motoneurons, and is a major genetic cause of infant mortality. Mutations in the SMN1 gene, which encodes the protein survival motor neuron (SMN), are responsible for the disease due to compensation deficit. SMN belongs to the Tudor domain protein family, whose members are known to interact with methylated arginine (R) or lysine (K) residues. SMN has well-defined roles in the metabolism of small non-coding ribonucleoproteins (snRNPs) and spliceosome activity. We previously showed that SMN relocated to damaged interphase centromeres, together with the Cajal body-associated proteins coilin and fibrillarin, during the so-called interphase centromere damage response (iCDR). Here we reveal that SMN is a chromatin-binding protein that specifically interacts with methylated histone H3K79, a gene expression- and splicing-associated histone modification. SMN relocation to damaged centromeres requires its functional Tudor domain and activity of the H3K79 methyltransferase DOT1-L. In vitro pull-down assays showed that SMN interacts with H3K79me1,2 via its functional Tudor domain. Chromatin immunoprecipitation confirmed that SMN binds to H3K79me1,2-containing chromatin in iCDR-induced cells. These data reveal a novel SMN property in the detection of specific chromatin modifications, and shed new light on the involvement of a putative epigenetic dimension to the occurrence of SMA.
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26
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Girard C, Will CL, Peng J, Makarov EM, Kastner B, Lemm I, Urlaub H, Hartmuth K, Lührmann R. Post-transcriptional spliceosomes are retained in nuclear speckles until splicing completion. Nat Commun 2012; 3:994. [PMID: 22871813 DOI: 10.1038/ncomms1998] [Citation(s) in RCA: 170] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 07/10/2012] [Indexed: 12/26/2022] Open
Abstract
There is little quantitative information regarding how much splicing occurs co-transcriptionally in higher eukaryotes, and it remains unclear where precisely splicing occurs in the nucleus. Here we determine the global extent of co- and post-transcriptional splicing in mammalian cells, and their respective subnuclear locations, using antibodies that specifically recognize phosphorylated SF3b155 (P-SF3b155) found only in catalytically activated/active spliceosomes. Quantification of chromatin- and nucleoplasm-associated P-SF3b155 after fractionation of HeLa cell nuclei, reveals that ~80% of pre-mRNA splicing occurs co-transcriptionally. Active spliceosomes localize in situ to regions of decompacted chromatin, at the periphery of or within nuclear speckles. Immunofluorescence microscopy with anti-P-SF3b155 antibodies, coupled with transcription inhibition and a block in splicing after SF3b155 phosphorylation, indicates that post-transcriptional splicing occurs in nuclear speckles and that release of post-transcriptionally spliced mRNA from speckles is coupled to the nuclear mRNA export pathway. Our data provide new insights into when and where splicing occurs in cells.
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Affiliation(s)
- Cyrille Girard
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
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27
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Machyna M, Heyn P, Neugebauer KM. Cajal bodies: where form meets function. WILEY INTERDISCIPLINARY REVIEWS-RNA 2012; 4:17-34. [PMID: 23042601 DOI: 10.1002/wrna.1139] [Citation(s) in RCA: 132] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The cell nucleus contains dozens of subcompartments that separate biochemical processes into confined spaces. Cajal bodies (CBs) were discovered more than 100 years ago, but only extensive research in the past decades revealed the surprising complexity of molecular and cellular functions taking place in these structures. Many protein and RNA species are modified and assembled within CBs, which have emerged as a meeting place and factory for ribonucleoprotein (RNP) particles involved in splicing, ribosome biogenesis and telomere maintenance. Recently, a distinct structure near histone gene clusters--the Histone locus body (HLB)--was discovered. Involved in histone mRNA 3'-end formation, HLBs can share several components with CBs. Whether the appearance of distinct HLBs is simply a matter of altered affinity between these structures or of an alternate mode of CB assembly is unknown. However, both structures share basic assembly properties, in which transcription plays a decisive role in initiation. After this seeding event, additional components associate in random order. This appears to be a widespread mechanism for body assembly. CB assembly encompasses an additional layer of complexity, whereby a set of pre-existing substructures can be integrated into mature CBs. We propose this as a multi-seeding model of CB assembly.
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Affiliation(s)
- Martin Machyna
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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28
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Clelland AK, Bales ABE, Sleeman JE. Changes in intranuclear mobility of mature snRNPs provide a mechanism for splicing defects in spinal muscular atrophy. J Cell Sci 2012; 125:2626-37. [PMID: 22393244 PMCID: PMC3403233 DOI: 10.1242/jcs.096867] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
It is becoming increasingly clear that defects in RNA metabolism can lead to disease. Spinal muscular atrophy (SMA), a leading genetic cause of infant mortality, results from insufficient amounts of survival motor neuron (SMN) protein. SMN is required for the biogenesis of small nuclear ribonucleoproteins (snRNPs): essential components of the spliceosome. Splicing abnormalities have been detected in models of SMA but it is unclear how lowered SMN affects the fidelity of pre-mRNA splicing. We have examined the dynamics of mature snRNPs in cells depleted of SMN and demonstrated that SMN depletion increases the mobility of mature snRNPs within the nucleus. To dissect the molecular mechanism by which SMN deficiency affects intranuclear snRNP mobility, we employed a panel of inhibitors of different stages of pre-mRNA processing. This in vivo modelling demonstrates that snRNP mobility is altered directly as a result of impaired snRNP maturation. Current models of nuclear dynamics predict that subnuclear structures, including the spliceosome, form by self-organization mediated by stochastic interactions between their molecular components. Thus, alteration of the intranuclear mobility of snRNPs provides a molecular mechanism for splicing defects in SMA.
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Takata H, Nishijima H, Maeshima K, Shibahara KI. The integrator complex is required for integrity of Cajal bodies. J Cell Sci 2012; 125:166-75. [PMID: 22250197 DOI: 10.1242/jcs.090837] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nucleus in eukaryotic cells is a highly organized and dynamic structure containing numerous subnuclear bodies. The morphological appearance of nuclear bodies seems to be a reflection of ongoing functions, such as DNA replication, transcription, repair, RNA processing and RNA transport. The integrator complex mediates processing of small nuclear RNA (snRNA), so it might play a role in nuclear body formation. Here, we show that the integrator complex is essential for integrity of the Cajal body. Depletion of INTS4, an integrator complex subunit, abrogated 3'-end processing of snRNA. A defect in this activity caused a significant accumulation of the Cajal body marker protein coilin in nucleoli. Some fractions of coilin still formed nucleoplasmic foci; however, they were free of other Cajal body components, such as survival of motor neuron protein (SMN), Sm proteins and snRNAs. SMN and Sm proteins formed striking cytoplasmic granules. These findings demonstrate that the integrator complex is essential for snRNA maturation and Cajal body homeostasis.
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Affiliation(s)
- Hideaki Takata
- Department of Integrated Genetics, National Institute of Genetics, Research Organization of Information and Systems, Mishima, Japan.
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Deryusheva S, Choleza M, Barbarossa A, Gall JG, Bordonné R. Post-transcriptional modification of spliceosomal RNAs is normal in SMN-deficient cells. RNA (NEW YORK, N.Y.) 2012; 18:31-6. [PMID: 22124016 PMCID: PMC3261741 DOI: 10.1261/rna.030106.111] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The survival of motor neuron (SMN) protein plays an important role in the biogenesis of spliceosomal snRNPs and is one factor required for the integrity of nuclear Cajal bodies (CBs). CBs are enriched in small CB-specific (sca) RNAs, which guide the formation of pseudouridylated and 2'-O-methylated residues in the snRNAs. Because SMN-deficient cells lack typical CBs, we asked whether the modification of internal residues of major and minor snRNAs is defective in these cells. We mapped modified nucleotides in the major U2 and the minor U4atac and U12 snRNAs. Using both radioactive and fluorescent primer extension approaches, we found that modification of major and minor spliceosomal snRNAs is normal in SMN-deficient cells. Our experiments also revealed a previously undetected pseudouridine at position 60 in human U2 and 2'-O-methylation of A1, A2, and G19 in human U4atac. These results confirm, and extend to minor snRNAs, previous experiments showing that scaRNPs can function in the absence of typical CBs. Furthermore, they show that the differential splicing defects in SMN-deficient cells are not due to failure of post-transcriptional modification of either major or minor snRNAs.
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Affiliation(s)
| | - Maria Choleza
- Institut de Génétique Moléculaire de Montpellier (IGMM), CNRS UMR 5535/IFR122, Université Montpellier, 34293 Montpellier Cedex 5, France
| | - Adrien Barbarossa
- Institut de Génétique Moléculaire de Montpellier (IGMM), CNRS UMR 5535/IFR122, Université Montpellier, 34293 Montpellier Cedex 5, France
| | | | - Rémy Bordonné
- Institut de Génétique Moléculaire de Montpellier (IGMM), CNRS UMR 5535/IFR122, Université Montpellier, 34293 Montpellier Cedex 5, France
- Corresponding author.E-mail .
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Rajendra T, Praveen K, Matera AG. Genetic analysis of nuclear bodies: from nondeterministic chaos to deterministic order. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2011; 75:365-74. [PMID: 21467138 PMCID: PMC4062921 DOI: 10.1101/sqb.2010.75.043] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The eukaryotic nucleus is a congested place, and macromolecular crowding is thought to have an important role in increasing the relative concentrations of nuclear proteins, thereby accelerating the rates of biochemical reactions. Crowding is also thought to provide the environment needed for formation of nuclear bodies/subcompartments, such as the Cajal body (CB) and the histone locus body (HLB), via self-organization. In this chapter, we contrast the theories of stochastic self-organization and hierarchical self-organization in their application to nuclear body assembly, using CBs and HLBs as paradigms. Genetic ablation studies in Drosophila on components of CBs and HLBs have revealed an order to the assembly of these structures that is suggestive of a hierarchical model of self-organization. These studies also show that functions attributed to the nuclear bodies are largely unaffected in their absence, reinforcing an emerging theme in the field that the purpose of these subdomains may be to enhance the efficiency and specificity of reactions.
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Affiliation(s)
- T.K. Rajendra
- Departments of Biology and Genetics, Program in Molecular Biology & Biotechnology, Lineberger Comprehensive Cancer Center University of North Carolina, Chapel Hill, NC 27599
| | - Kavita Praveen
- Departments of Biology and Genetics, Program in Molecular Biology & Biotechnology, Lineberger Comprehensive Cancer Center University of North Carolina, Chapel Hill, NC 27599
| | - A. Gregory Matera
- Departments of Biology and Genetics, Program in Molecular Biology & Biotechnology, Lineberger Comprehensive Cancer Center University of North Carolina, Chapel Hill, NC 27599
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Hydrogen peroxide decreases the survival rate of HeLa cells with stable knockdown of survival motor neuron protein. Kaohsiung J Med Sci 2011; 27:102-7. [DOI: 10.1016/j.kjms.2010.11.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Accepted: 11/17/2010] [Indexed: 11/18/2022] Open
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Boulisfane N, Choleza M, Rage F, Neel H, Soret J, Bordonné R. Impaired minor tri-snRNP assembly generates differential splicing defects of U12-type introns in lymphoblasts derived from a type I SMA patient. Hum Mol Genet 2010; 20:641-8. [PMID: 21098506 DOI: 10.1093/hmg/ddq508] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The survival of motor neuron (SMN) protein is essential for cytoplasmic assembly of spliceosomal snRNPs. Although the normal proportion of endogenous snRNAs is unevenly altered in spinal muscular atrophy (SMA) tissues, the biogenesis of individual snRNPs is not dramatically affected in SMN-deficient cells. The SMN protein is also required for normal Cajal body (CB) formation, but the functional consequences of CB disruption upon SMN deficiency have not yet been analyzed at the level of macromolecular snRNPs assembly. Here, we show that the SMN protein is required for tri-snRNPs formation and that the level of the minor U4atac/U6atac/U5 tri-snRNPs is dramatically decreased in lymphoblasts derived from a patient suffering from a severe form of SMA. We found also that splicing of some, but not all, minor introns is inhibited in these cells, demonstrating links between SMN deficiency and differential alterations of splicing events mediated by the minor spliceosome. Our results suggest that SMA might result from the inefficient splicing of one or only a few pre-mRNAs carrying minor introns and coding for proteins required for motor neurons function and/or organization.
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Affiliation(s)
- Nawal Boulisfane
- Institut de Génétique Moléculaire de Montpellier (IGMM), CNRS UMR 5535/IFR122, Université Montpellier I and II,1919 route de Mende, 34293 Montpellier Cedex 5, France
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Mahmoudi S, Henriksson S, Weibrecht I, Smith S, Söderberg O, Strömblad S, Wiman KG, Farnebo M. WRAP53 is essential for Cajal body formation and for targeting the survival of motor neuron complex to Cajal bodies. PLoS Biol 2010; 8:e1000521. [PMID: 21072240 PMCID: PMC2970535 DOI: 10.1371/journal.pbio.1000521] [Citation(s) in RCA: 104] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Accepted: 09/03/2010] [Indexed: 02/02/2023] Open
Abstract
The WRAP53 gene gives rise to a p53 antisense transcript that regulates p53. This gene also encodes a protein that directs small Cajal body-specific RNAs to Cajal bodies. Cajal bodies are nuclear organelles involved in diverse functions such as processing ribonucleoproteins important for splicing. Here we identify the WRAP53 protein as an essential factor for Cajal body maintenance and for directing the survival of motor neuron (SMN) complex to Cajal bodies. By RNA interference and immunofluorescence we show that Cajal bodies collapse without WRAP53 and that new Cajal bodies cannot be formed. By immunoprecipitation we find that WRAP53 associates with the Cajal body marker coilin, the splicing regulatory protein SMN, and the nuclear import receptor importinβ, and that WRAP53 is essential for complex formation between SMN-coilin and SMN-importinβ. Furthermore, depletion of WRAP53 leads to accumulation of SMN in the cytoplasm and prevents the SMN complex from reaching Cajal bodies. Thus, WRAP53 mediates the interaction between SMN and associated proteins, which is important for nuclear targeting of SMN and the subsequent localization of the SMN complex to Cajal bodies. Moreover, we detect reduced WRAP53-SMN binding in patients with spinal muscular atrophy, which is the leading genetic cause of infant mortality worldwide, caused by mutations in SMN1. This suggests that loss of WRAP53-mediated SMN trafficking contributes to spinal muscular atrophy.
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Affiliation(s)
- Salah Mahmoudi
- Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden
| | - Sofia Henriksson
- Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden
| | - Irene Weibrecht
- Department of Genetics and Pathology, Rudbeck Laboratory, University of Uppsala, Uppsala, Sweden
| | - Stephen Smith
- Center for Biosciences, Department of Biosciences and Nutrition, Novum, Karolinska Institutet, Huddinge, Sweden
| | - Ola Söderberg
- Department of Genetics and Pathology, Rudbeck Laboratory, University of Uppsala, Uppsala, Sweden
| | - Staffan Strömblad
- Center for Biosciences, Department of Biosciences and Nutrition, Novum, Karolinska Institutet, Huddinge, Sweden
| | - Klas G. Wiman
- Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden
| | - Marianne Farnebo
- Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden
- * E-mail:
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Zhang J, Zhang F, Zheng X. Depletion of hCINAP by RNA interference causes defects in Cajal body formation, histone transcription, and cell viability. Cell Mol Life Sci 2010; 67:1907-18. [PMID: 20186459 PMCID: PMC11115741 DOI: 10.1007/s00018-010-0301-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 01/25/2010] [Accepted: 02/02/2010] [Indexed: 10/19/2022]
Abstract
hCINAP is a highly conserved and ubiquitously expressed protein in eukaryotic organisms and its overexpression decreases the average number of Cajal bodies (CBs) with diverse nuclear functions. Here, we report that hCINAP is associated with important components of CBs. Depletion of hCINAP by RNA interference causes defects in CB formation and disrupts subcellular localizations of its components including coilin, survival motor neurons protein, spliceosomal small nuclear ribonucleoproteins, and nuclear protein ataxia-telangiectasia. Moreover, knockdown of hCINAP expression results in marked reduction of histone transcription, lower levels of U small nuclear RNAs (U1, U2, U4, and U5), and a loss of cell viability. Detection of increased caspase-3 activities in hCINAP-depleted cells indicate that apoptosis is one of the reasons for the loss of viability. Altogether, these data suggest that hCINAP is essential for the formation of canonical CBs, histone transcription, and cell viability.
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Affiliation(s)
- Jinfang Zhang
- National Laboratory of Protein Engineering and Plant Genetic Engineering, Peking University, Beijing, 100871 China
- Department of Biochemistry and Molecular Biology, College of Life Sciences, Peking University, Beijing, 100871 China
| | - Feiyun Zhang
- Department of Biochemistry and Molecular Biology, College of Life Sciences, Capital Normal University, Beijing, 100037 China
| | - Xiaofeng Zheng
- National Laboratory of Protein Engineering and Plant Genetic Engineering, Peking University, Beijing, 100871 China
- Department of Biochemistry and Molecular Biology, College of Life Sciences, Peking University, Beijing, 100871 China
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Hebert MD. Phosphorylation and the Cajal body: modification in search of function. Arch Biochem Biophys 2010; 496:69-76. [PMID: 20193656 PMCID: PMC2850958 DOI: 10.1016/j.abb.2010.02.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Accepted: 02/24/2010] [Indexed: 12/25/2022]
Abstract
The Cajal body (CB) is a subnuclear domain that contains proteins and factors involved in a diverse range of activities including ribonucleoprotein maturation, histone gene transcription and telomerase assembly. Among these activities, the CBs' role in small nuclear ribonucleoprotein (snRNP) biogenesis is best characterized. Although CBs are found in plants, flies and mammals, not all cell types contain CBs. Rather, CBs are most prominent in transcriptionally active cells, such as cancer and neuronal cells. Many CB components, including the CB marker protein coilin, are phosphorylated in humans. The functional consequence of phosphorylation on CB assembly, activity and disassembly is largely unknown. Also unknown are the signaling pathways, kinases and phosphatases that act upon proteins which localize in the CB. The goal of this review is to demonstrate the need for a concerted effort towards elucidating the functional consequence of phosphorylation on CB formation and activity.
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Affiliation(s)
- Michael D Hebert
- Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216-4505, USA
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Clelland AK, Kinnear NP, Oram L, Burza J, Sleeman JE. The SMN protein is a key regulator of nuclear architecture in differentiating neuroblastoma cells. Traffic 2009; 10:1585-98. [PMID: 19735367 PMCID: PMC2788272 DOI: 10.1111/j.1600-0854.2009.00972.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The cell nucleus contains two closely related structures, Cajal bodies (CBs) and gems. CBs are the first site of accumulation of newly assembled splicing snRNPs (small nuclear ribonucleoproteins) following their import into the nucleus, before they form their steady-state localization in nuclear splicing speckles. Gems are the nuclear site of accumulation of survival motor neurons (SMNs), an insufficiency of which leads to the inherited neurodegenerative condition, spinal muscular atrophy (SMA). SMN is required in the cytoplasm for the addition of core, Sm, proteins to new snRNPs and is believed to accompany snRNPs to the CB. In most cell lines, gems are indistinguishable from CBs, although the structures are often separate in vivo. The relationship between CBs and gems is not fully understood, but there is evidence that symmetrical dimethylation of arginine residues in the CB protein coilin brings them together in HeLa cells. During neuronal differentiation of the human neuroblastoma cell line SH-SY5Y, CBs and gems increase their colocalization, mimicking changes seen during foetal development. This does not result from alterations in the methylation of coilin, but from increased levels of SMN. Expression of exogenous SMN results in an increased efficiency of snRNP transport to nuclear speckles. This suggests different mechanisms are present in different cell types and in vivo that may be significant for the tissue-specific pathology of SMA.
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Affiliation(s)
- Allyson K Clelland
- School of Biology, University of St Andrews, Bute Medical Buildings, St Andrews, Fife KY16 9TS, UK
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Fibroblast growth factor-2 regulates the stability of nuclear bodies. Proc Natl Acad Sci U S A 2009; 106:12747-52. [PMID: 19617559 DOI: 10.1073/pnas.0900122106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nuclear bodies are distinct subnuclear structures. The survival of motoneuron (SMN) gene is mutated or deleted in patients with the neurodegenerative disease spinal muscular atrophy (SMA). The gene product SMN is a marker protein for one class of nuclear bodies denoted as nuclear gems. SMN has also been found in Cajal bodies, which co-localize with gems in many cell types. Interestingly, SMA patients display a reduced number of gems. Little is known about the regulation of nuclear body formation and stabilization. We have previously shown that a nuclear isoform of the fibroblast growth factor-2 (FGF-2(23)) binds directly to SMN. In this study, we analyzed the consequences of FGF-2(23) binding to SMN with regard to nuclear body formation. On a molecular level, we showed that FGF-2(23) competed with Gemin2 (a component of the SMN complex that is necessary for gem stabilization) for binding to SMN. Down-regulation of Gemin2 by siRNA caused destabilization of SMN-positive nuclear bodies. This process is reflected in both cellular and in vivo systems by a negative regulatory function of FGF-2 in nuclear body formation: in HEK293 cells, FGF-2(23) decreased the number of SMN-positive nuclear bodies. The same effect could be observed in motoneurons of FGF-2 transgenic mice. This study demonstrates the functional role of a growth factor in the regulation of structural entities of the nucleus.
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Hearst SM, Gilder AS, Negi SS, Davis MD, George EM, Whittom AA, Toyota CG, Husedzinovic A, Gruss OJ, Hebert MD. Cajal-body formation correlates with differential coilin phosphorylation in primary and transformed cell lines. J Cell Sci 2009; 122:1872-81. [PMID: 19435804 DOI: 10.1242/jcs.044040] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Cajal bodies (CBs) are nuclear structures that are thought to have diverse functions, including small nuclear ribonucleoprotein (snRNP) biogenesis. The phosphorylation status of coilin, the CB marker protein, might impact CB formation. We hypothesize that primary cells, which lack CBs, contain different phosphoisoforms of coilin compared with that found in transformed cells, which have CBs. Localization, self-association and fluorescence recovery after photobleaching (FRAP) studies on coilin phosphomutants all suggest this modification impacts the function of coilin and may thus contribute towards CB formation. Two-dimensional gel electrophoresis demonstrates that coilin is hyperphosphorylated in primary cells compared with transformed cells. mRNA levels of the nuclear phosphatase PPM1G are significantly reduced in primary cells and expression of PPM1G in primary cells induces CBs. Additionally, PPM1G can dephosphorylate coilin in vitro. Surprisingly, however, expression of green fluorescent protein alone is sufficient to form CBs in primary cells. Taken together, our data support a model whereby coilin is the target of an uncharacterized signal transduction cascade that responds to the increased transcription and snRNP demands found in transformed cells.
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Affiliation(s)
- Scoty M Hearst
- Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216, USA
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Renvoisé B, Colasse S, Burlet P, Viollet L, Meier UT, Lefebvre S. The loss of the snoRNP chaperone Nopp140 from Cajal bodies of patient fibroblasts correlates with the severity of spinal muscular atrophy. Hum Mol Genet 2009; 18:1181-9. [PMID: 19129172 DOI: 10.1093/hmg/ddp009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Spinal muscular atrophy (SMA) is a common autosomal recessive neurodegenerative disease caused by reduced survival motor neuron (SMN) levels. The assembly machinery containing SMN is implicated in the biogenesis of the spliceosomal small nuclear ribonucleoproteins (snRNPs). SMN is present in both the cytoplasm and nucleus, where it transiently accumulates in subnuclear domains named Cajal bodies (CBs) and functions in the maturation of snRNPs and small nucleolar (sno)RNPs. The impact of lowering SMN levels on the composition of CBs in SMA cells is still not completely understood. Here, we analyse the CB composition in immortalized and primary fibroblasts from SMA patients. We show that the U snRNA export factors PHAX and chromosome region maintenance 1 and the box C/D snoRNP core protein fibrillarin concentrate in CBs from SMA cells, whereas the box H/ACA core proteins GAR1 and NAP57/dyskerin show reduced CB localization. Remarkably, the functional deficiency in SMA cells is associated with decreased localization of the snoRNP chaperone Nopp140 in CBs that correlates with disease severity. Indeed, RNA interference knockdown experiments in control fibroblasts demonstrate that SMN is required for accumulation of Nopp140 in CBs. Conversely, overexpression of SMN in SMA cells restores the CB localization of Nopp140, whereas SMN mutants found in SMA patients are defective in promoting the association of Nopp140 with CBs. Taken together, we demonstrate that only a subset of CB functions (as indicated by the association of representative factors) are impaired in SMA cells and, importantly, we identify the decrease of Nopp140 localization in CBs as a phenotypic marker for SMA.
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Affiliation(s)
- Benoît Renvoisé
- Laboratoire de Biologie Cellulaire des Membranes, Department of Cell Biology, Institut Jacques Monod (IJM), UMR 7592 CNRS/Universités Paris 6 et 7, Paris Cedex 05, France
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Turner BJ, Bäumer D, Parkinson NJ, Scaber J, Ansorge O, Talbot K. TDP-43 expression in mouse models of amyotrophic lateral sclerosis and spinal muscular atrophy. BMC Neurosci 2008; 9:104. [PMID: 18957104 PMCID: PMC2583980 DOI: 10.1186/1471-2202-9-104] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2008] [Accepted: 10/28/2008] [Indexed: 12/12/2022] Open
Abstract
Background Redistribution of nuclear TAR DNA binding protein 43 (TDP-43) to the cytoplasm and ubiquitinated inclusions of spinal motor neurons and glial cells is characteristic of amyotrophic lateral sclerosis (ALS) pathology. Recent evidence suggests that TDP-43 pathology is common to sporadic ALS and familial ALS without SOD1 mutation, but not SOD1-related fALS cases. Furthermore, it remains unclear whether TDP-43 abnormalities occur in non-ALS forms of motor neuron disease. Here, we characterise TDP-43 localisation, expression levels and post-translational modifications in mouse models of ALS and spinal muscular atrophy (SMA). Results TDP-43 mislocalisation to ubiquitinated inclusions or cytoplasm was notably lacking in anterior horn cells from transgenic mutant SOD1G93A mice. In addition, abnormally phosphorylated or truncated TDP-43 species were not detected in fractionated ALS mouse spinal cord or brain. Despite partial colocalisation of TDP-43 with SMN, depletion of SMN- and coilin-positive Cajal bodies in motor neurons of affected SMA mice did not alter nuclear TDP-43 distribution, expression or biochemistry in spinal cords. Conclusion These results emphasise that TDP-43 pathology characteristic of human sporadic ALS is not a core component of the neurodegenerative mechanisms caused by SOD1 mutation or SMN deficiency in mouse models of ALS and SMA, respectively.
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Affiliation(s)
- Bradley J Turner
- University of Oxford, MRC Functional Genetics Unit, Department of Physiology, Anatomy and Genetics, South Parks Road, Oxford, OX1 3QX, UK.
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Shpargel KB, Praveen K, Rajendra TK, Matera AG. Gemin3 is an essential gene required for larval motor function and pupation in Drosophila. Mol Biol Cell 2008; 20:90-101. [PMID: 18923150 DOI: 10.1091/mbc.e08-01-0024] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The assembly of metazoan Sm-class small nuclear ribonucleoproteins (snRNPs) is an elaborate, step-wise process that takes place in multiple subcellular compartments. The initial steps, including formation of the core RNP, are mediated by the survival motor neuron (SMN) protein complex. Loss-of-function mutations in human SMN1 result in a neuromuscular disease called spinal muscular atrophy. The SMN complex is comprised of SMN and a number of tightly associated proteins, collectively called Gemins. In this report, we identify and characterize the fruitfly ortholog of the DEAD box protein, Gemin3. Drosophila Gemin3 (dGem3) colocalizes and interacts with dSMN in vitro and in vivo. RNA interference for dGem3 codepletes dSMN and inhibits efficient Sm core assembly in vitro. Transposon insertion mutations in Gemin3 are larval lethals and also codeplete dSMN. Transgenic overexpression of dGem3 rescues lethality, but overexpression of dSMN does not, indicating that loss of dSMN is not the primary cause of death. Gemin3 mutant larvae exhibit motor defects similar to previously characterized Smn alleles. Remarkably, appreciable numbers of Gemin3 mutants (along with one previously undescribed Smn allele) survive as larvae for several weeks without pupating. Our results demonstrate the conservation of Gemin3 protein function in metazoan snRNP assembly and reveal that loss of either Smn or Gemin3 can contribute to neuromuscular dysfunction.
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Affiliation(s)
- Karl B Shpargel
- Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4955, USA
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Parker GC, Li X, Anguelov RA, Toth G, Cristescu A, Acsadi G. Survival motor neuron protein regulates apoptosis in an in vitro model of spinal muscular atrophy. Neurotox Res 2008; 13:39-48. [PMID: 18367439 DOI: 10.1007/bf03033366] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Progressive spinal muscular atrophy (SMA), the most prevalent hereditary lower motor neuron disease, is caused by mutations in the telomeric copy of the survival of motor neuron (SMN1) gene. Unlike other cells, lower motor neurons cannot tolerate low levels of smn protein. However, it is unclear as to the nature of the cell death involved. There is evidence that lower motor neurons undergo apoptosis in SMA, leading to muscle weakness and wasting. This study investigated whether SMN1 regulation in a motor neuron model affected indices of apoptotic cell death. Decreased smn expression in neuroblastoma hybrid (NSC-34) cell lines by small interfering RNA (siRNA) was demonstrated at the mRNA and protein level. Smn-depleted cells showed elevated caspase-3 activity, decreased cell viability and increased percentage of TUNEL positive cells. Conversely, NSC-34 cell smn overexpression by adenoviral gene transfer decreased staurosporine-induced caspase-3 elevation and mitigated induced cell toxicity as assessed by 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. However, increased smn expression by itself did not increase cell viability. These data suggest not only that decreased smn levels increase apoptosis in an in vitro model of SMA, but also that increased smn can protect against neural injury.
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Affiliation(s)
- Graham C Parker
- Carman and Ann Adams Department of Pediatrics, Wayne State University, Detroit, MI, USA
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Woulfe J. Nuclear bodies in neurodegenerative disease. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:2195-206. [PMID: 18539152 DOI: 10.1016/j.bbamcr.2008.05.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 03/31/2008] [Accepted: 05/08/2008] [Indexed: 12/12/2022]
Abstract
Neurodegenerative diseases are characterized by a relentlessly progressive loss of the functional and structural integrity of the central nervous system. In many cases, these diseases arise sporadically and the causes are unknown. The abnormal aggregation of protein within the cytoplasm or the nucleus of brain cells represents a unifying pathological feature of these diseases. There is increasing evidence for nuclear dysfunction in neurodegenerative diseases. How this relates to protein aggregation in the context of "cause and effect" remains to be determined in most cases. Co-ordinated nuclear function is predicated on the activity of distinct nuclear subdomains, or nuclear bodies, each responsible for a specific function. If nuclear dysfunction represents an important etiopathological feature in neurodegenerative disease, then this should be reflected by functional and/or morphological alterations in this nuclear compartmentalization. For most neurodegenerative diseases, evidence for nuclear dysfunction, with attendant consequences for nuclear architecture, is only beginning to emerge. In this review, I will discuss neurodegenerative diseases in the context of nuclear dysfunction and, more specifically, alterations in nuclear bodies. Although research in this field is in its infancy, identifying alterations in the nucleus in neurodegenerative disease has potentially profound implications for elucidating the pathogenesis of these disorders.
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Affiliation(s)
- John Woulfe
- Department of Pathology, The Ottawa Hospital, Civic Campus, 1053 Carling Avenue, Ottawa, Ontario, Canada K1Y 4E9.
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Stanek D, Pridalová-Hnilicová J, Novotný I, Huranová M, Blazíková M, Wen X, Sapra AK, Neugebauer KM. Spliceosomal small nuclear ribonucleoprotein particles repeatedly cycle through Cajal bodies. Mol Biol Cell 2008; 19:2534-43. [PMID: 18367544 DOI: 10.1091/mbc.e07-12-1259] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Cajal body (CB) is a nuclear structure closely associated with import and biogenesis of small nuclear ribonucleoprotein particles (snRNPs). Here, we tested whether CBs also contain mature snRNPs and whether CB integrity depends on the ongoing snRNP splicing cycle. Sm proteins tagged with photoactivatable and color-maturing variants of fluorescent proteins were used to monitor snRNP behavior in living cells over time; mature snRNPs accumulated in CBs, traveled from one CB to another, and they were not preferentially replaced by newly imported snRNPs. To test whether CB integrity depends on the snRNP splicing cycle, two human orthologues of yeast proteins involved in distinct steps in spliceosome disassembly after splicing, hPrp22 and hNtr1, were depleted by small interfering RNA treatment. Surprisingly, depletion of either protein led to the accumulation of U4/U6 snRNPs in CBs, suggesting that reassembly of the U4/U6.U5 tri-snRNP was delayed. Accordingly, a relative decrease in U5 snRNPs compared with U4/U6 snRNPs was observed in CBs, as well as in nuclear extracts of treated cells. Together, the data show that particular phases of the spliceosome cycle are compartmentalized in living cells, with reassembly of the tri-snRNP occurring in CBs.
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Affiliation(s)
- David Stanek
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic.
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47
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Boulon S, Marmier-Gourrier N, Pradet-Balade B, Wurth L, Verheggen C, Jády BE, Rothé B, Pescia C, Robert MC, Kiss T, Bardoni B, Krol A, Branlant C, Allmang C, Bertrand E, Charpentier B. The Hsp90 chaperone controls the biogenesis of L7Ae RNPs through conserved machinery. ACTA ACUST UNITED AC 2008; 180:579-95. [PMID: 18268104 PMCID: PMC2234240 DOI: 10.1083/jcb.200708110] [Citation(s) in RCA: 177] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
RNA-binding proteins of the L7Ae family are at the heart of many essential ribonucleoproteins (RNPs), including box C/D and H/ACA small nucleolar RNPs, U4 small nuclear RNP, telomerase, and messenger RNPs coding for selenoproteins. In this study, we show that Nufip and its yeast homologue Rsa1 are key components of the machinery that assembles these RNPs. We observed that Rsa1 and Nufip bind several L7Ae proteins and tether them to other core proteins in the immature particles. Surprisingly, Rsa1 and Nufip also link assembling RNPs with the AAA + adenosine triphosphatases hRvb1 and hRvb2 and with the Hsp90 chaperone through two conserved adaptors, Tah1/hSpagh and Pih1. Inhibition of Hsp90 in human cells prevents the accumulation of U3, U4, and telomerase RNAs and decreases the levels of newly synthesized hNop58, hNHP2, 15.5K, and SBP2. Thus, Hsp90 may control the folding of these proteins during the formation of new RNPs. This suggests that Hsp90 functions as a master regulator of cell proliferation by allowing simultaneous control of cell signaling and cell growth.
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Affiliation(s)
- Séverine Boulon
- Institute of Molecular Genetics of Montpellier, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5535, Montpellier Cedex 5, France
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48
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Petri S, Grimmler M, Over S, Fischer U, Gruss OJ. Dephosphorylation of survival motor neurons (SMN) by PPM1G/PP2Cgamma governs Cajal body localization and stability of the SMN complex. ACTA ACUST UNITED AC 2007; 179:451-65. [PMID: 17984321 PMCID: PMC2064792 DOI: 10.1083/jcb.200704163] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The survival motor neuron (SMN) complex functions in maturation of uridine-rich small nuclear ribonucleoprotein (RNP) particles. SMN mediates the cytoplasmic assembly of Sm proteins onto uridine-rich small RNAs, and then participates in targeting RNPs to nuclear Cajal bodies (CBs). Recent studies have suggested that phosphorylation might control localization and function of the SMN complex. Here, we show that the nuclear phosphatase PPM1G/PP2Cgamma interacts with and dephosphorylates the SMN complex. Small interfering RNA knockdown of PPM1G leads to an altered phosphorylation pattern of SMN and Gemin3, loss of SMN from CBs, and reduced stability of SMN. Accumulation in CBs is restored upon overexpression of catalytically active, but not that of inactive, PPM1G. This demonstrates that PPM1G's phosphatase activity is necessary to maintain SMN subcellular distribution. Concomitant knockdown of unr interacting protein (unrip), a component implicated in cytoplasmic retention of the SMN complex, also rescues the localization defects. Our data suggest that an interplay between PPM1G and unrip determine compartment-specific phosphorylation patterns, localization, and function of the SMN complex.
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Affiliation(s)
- Sebastian Petri
- Zentrum für Molekulare Biologie der Universität Heidelberg, 69120 Heidelberg, Germany
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A stochastic view of spliceosome assembly and recycling in the nucleus. PLoS Comput Biol 2007; 3:2019-31. [PMID: 17967051 PMCID: PMC2041977 DOI: 10.1371/journal.pcbi.0030201] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Accepted: 09/04/2007] [Indexed: 12/16/2022] Open
Abstract
How splicing factors are recruited to nascent transcripts in the nucleus in order to assemble spliceosomes on newly synthesised pre-mRNAs is unknown. To address this question, we compared the intranuclear trafficking kinetics of small nuclear ribonucleoprotein particles (snRNP) and non-snRNP proteins in the presence and absence of splicing activity. Photobleaching experiments clearly show that spliceosomal proteins move continuously throughout the entire nucleus independently of ongoing transcription or splicing. Using quantitative experimental data, a mathematical model was applied for spliceosome assembly and recycling in the nucleus. The model assumes that splicing proteins move by Brownian diffusion and interact stochastically with binding sites located at different subnuclear compartments. Inhibition of splicing, which reduces the number of pre-mRNA binding sites available for spliceosome assembly, was modeled as a decrease in the on-rate binding constant in the nucleoplasm. Simulation of microscopy experiments before and after splicing inhibition yielded results consistent with the experimental observations. Taken together, our data argue against the view that spliceosomal components are stored in nuclear speckles until a signal triggers their recruitment to nascent transcripts. Rather, the results suggest that splicing proteins are constantly diffusing throughout the entire nucleus and collide randomly and transiently with pre-mRNAs. Understanding the genomic program of an organism requires knowledge of how the information encoded in DNA is processed to generate messenger RNAs that can be translated into proteins. The initial products of gene transcription are extensively modified in the cell nucleus, and a major processing reaction consists of splicing of specific sequences from the middle of the primary transcripts. Splicing is catalyzed by the spliceosome, a large complex composed of five small RNAs and over 100 different proteins. Spliceosomes form anew on primary transcripts and disassemble after splicing, but what triggers the recruitment of individual spliceosomal components to selected gene products is unclear. Here, we have combined imaging and computational approaches to address this question. We obtained quantitative experimental data on the mobility and subnuclear distribution of splicing proteins before and after splicing inhibition, and we applied mathematical models to analyze and interpret the results. We conclude that spliceosomal components do not require a signal in order to be recruited to nascent transcripts. Our results favor the view that splicing proteins are constantly diffusing throughout the entire nucleus and collide randomly and transiently with primary gene products.
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Gonsalvez GB, Tian L, Ospina JK, Boisvert FM, Lamond AI, Matera AG. Two distinct arginine methyltransferases are required for biogenesis of Sm-class ribonucleoproteins. ACTA ACUST UNITED AC 2007; 178:733-40. [PMID: 17709427 PMCID: PMC2064538 DOI: 10.1083/jcb.200702147] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Small nuclear ribonucleoproteins (snRNPs) are core components of the spliceosome. The U1, U2, U4, and U5 snRNPs each contain a common set of seven Sm proteins. Three of these Sm proteins are posttranslationally modified to contain symmetric dimethylarginine (sDMA) residues within their C-terminal tails. However, the precise function of this modification in the snRNP biogenesis pathway is unclear. Several lines of evidence suggest that the methyltransferase protein arginine methyltransferase 5 (PRMT5) is responsible for sDMA modification of Sm proteins. We found that in human cells, PRMT5 and a newly discovered type II methyltransferase, PRMT7, are each required for Sm protein sDMA modification. Furthermore, we show that the two enzymes function nonredundantly in Sm protein methylation. Lastly, we provide in vivo evidence demonstrating that Sm protein sDMA modification is required for snRNP biogenesis in human cells.
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Affiliation(s)
- Graydon B Gonsalvez
- Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
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