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Regulation of ribosomal RNA gene copy number, transcription and nucleolus organization in eukaryotes. Nat Rev Mol Cell Biol 2023; 24:414-429. [PMID: 36732602 DOI: 10.1038/s41580-022-00573-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/14/2022] [Indexed: 02/04/2023]
Abstract
One of the first biological machineries to be created seems to have been the ribosome. Since then, organisms have dedicated great efforts to optimize this apparatus. The ribosomal RNA (rRNA) contained within ribosomes is crucial for protein synthesis and maintenance of cellular function in all known organisms. In eukaryotic cells, rRNA is produced from ribosomal DNA clusters of tandem rRNA genes, whose organization in the nucleolus, maintenance and transcription are strictly regulated to satisfy the substantial demand for rRNA required for ribosome biogenesis. Recent studies have elucidated mechanisms underlying the integrity of ribosomal DNA and regulation of its transcription, including epigenetic mechanisms and a unique recombination and copy-number control system to stably maintain high rRNA gene copy number. In this Review, we disucss how the crucial maintenance of rRNA gene copy number through control of gene amplification and of rRNA production by RNA polymerase I are orchestrated. We also discuss how liquid-liquid phase separation controls the architecture and function of the nucleolus and the relationship between rRNA production, cell senescence and disease.
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Shetty PMV, Rangrez AY, Frey N. SUMO proteins in the cardiovascular system: friend or foe? J Biomed Sci 2020; 27:98. [PMID: 33099299 PMCID: PMC7585181 DOI: 10.1186/s12929-020-00689-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 09/16/2020] [Indexed: 02/07/2023] Open
Abstract
Post-translational modifications (PTMs) are crucial for the adaptation of various signalling pathways to ensure cellular homeostasis and proper adaptation to stress. PTM is a covalent addition of a small chemical functional group such as a phosphate group (phosphorylation), methyl group (methylation), or acetyl group (acetylation); lipids like hydrophobic isoprene polymers (isoprenylation); sugars such as a glycosyl group (glycosylation); or even small peptides such as ubiquitin (ubiquitination), SUMO (SUMOylation), NEDD8 (neddylation), etc. SUMO modification changes the function and/or fate of the protein especially under stress conditions, and the consequences of this conjugation can be appreciated from development to diverse disease processes. The impact of SUMOylation in disease has not been monotonous, rather SUMO is found playing a role on both sides of the coin either facilitating or impeding disease progression. Several recent studies have implicated SUMO proteins as key regulators in various cardiovascular disorders. The focus of this review is thus to summarize the current knowledge on the role of the SUMO family in the pathophysiology of cardiovascular diseases.
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Affiliation(s)
- Prithviraj Manohar Vijaya Shetty
- Department of Internal Medicine III (Cardiology, Angiology, Intensive Care), University Medical Center Kiel, Rosalind-Franklin Str. 12, 24105, Kiel, Germany
- Manipal Institute of Regenerative Medicine, MAHE-Bengaluru, Bangalore, India
| | - Ashraf Yusuf Rangrez
- Department of Internal Medicine III (Cardiology, Angiology, Intensive Care), University Medical Center Kiel, Rosalind-Franklin Str. 12, 24105, Kiel, Germany.
- DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Kiel, Germany.
| | - Norbert Frey
- Department of Internal Medicine III (Cardiology, Angiology, Intensive Care), University Medical Center Kiel, Rosalind-Franklin Str. 12, 24105, Kiel, Germany.
- DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Kiel, Germany.
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Lafita-Navarro MDC, Blanco R, Mata-Garrido J, Liaño-Pons J, Tapia O, García-Gutiérrez L, García-Alegría E, Berciano MT, Lafarga M, León J. MXD1 localizes in the nucleolus, binds UBF and impairs rRNA synthesis. Oncotarget 2018; 7:69536-69548. [PMID: 27588501 PMCID: PMC5342496 DOI: 10.18632/oncotarget.11766] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 08/26/2016] [Indexed: 12/16/2022] Open
Abstract
MXD1 is a protein that interacts with MAX, to form a repressive transcription factor. MXD1-MAX binds E-boxes. MXD1-MAX antagonizes the transcriptional activity of the MYC oncoprotein in most models. It has been reported that MYC overexpression leads to augmented RNA synthesis and ribosome biogenesis, which is a relevant activity in MYC-mediated tumorigenesis. Here we describe that MXD1, but not MYC or MNT, localizes to the nucleolus in a wide array of cell lines derived from different tissues (carcinoma, leukemia) as well as in embryonic stem cells. MXD1 also localizes in the nucleolus of primary tissue cells as neurons and Sertoli cells. The nucleolar localization of MXD1 was confirmed by co-localization with UBF. Co-immunoprecipitation experiments showed that MXD1 interacted with UBF and proximity ligase assays revealed that this interaction takes place in the nucleolus. Furthermore, chromatin immunoprecipitation assays showed that MXD1 was bound in the transcribed rDNA chromatin, where it co-localizes with UBF, but also in the ribosomal intergenic regions. The MXD1 involvement in rRNA synthesis was also suggested by the nucleolar segregation upon rRNA synthesis inhibition by actinomycin D. Silencing of MXD1 with siRNAs resulted in increased synthesis of pre-rRNA while enforced MXD1 expression reduces it. The results suggest a new role for MXD1, which is the control of ribosome biogenesis. This new MXD1 function would be important to curb MYC activity in tumor cells.
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Affiliation(s)
- Maria Del Carmen Lafita-Navarro
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain.,Present address: Department of Cell Biology, UT Southwestern Medical Center, Dallas, Texas, USA
| | - Rosa Blanco
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain
| | - Jorge Mata-Garrido
- Department of Anatomy and Cell Biology and Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED), University of Cantabria-IDIVAL, Santander, Spain
| | - Judit Liaño-Pons
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain
| | - Olga Tapia
- Department of Anatomy and Cell Biology and Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED), University of Cantabria-IDIVAL, Santander, Spain
| | - Lucía García-Gutiérrez
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain
| | - Eva García-Alegría
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain.,Present address: Stem Cell Hematopoiesis Group, Cancer Research UK Manchester Institute, University of Manchester, Manchester, United Kingdom
| | - María T Berciano
- Department of Anatomy and Cell Biology and Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED), University of Cantabria-IDIVAL, Santander, Spain
| | - Miguel Lafarga
- Department of Anatomy and Cell Biology and Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED), University of Cantabria-IDIVAL, Santander, Spain
| | - Javier León
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), CSIC-Universidad de Cantabria, and Department of Molecular Biology, University of Cantabria, Santander, Spain
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4
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Duncan FE, Jasti S, Paulson A, Kelsh JM, Fegley B, Gerton JL. Age-associated dysregulation of protein metabolism in the mammalian oocyte. Aging Cell 2017; 16:1381-1393. [PMID: 28994181 PMCID: PMC5676066 DOI: 10.1111/acel.12676] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/16/2017] [Indexed: 12/21/2022] Open
Abstract
Reproductive aging is characterized by a marked decline in oocyte quality that contributes to infertility, miscarriages, and birth defects. This decline is multifactorial, and the underlying mechanisms are under active investigation. Here, we performed RNA-Seq on individual growing follicles from reproductively young and old mice to identify age-dependent functions in oocytes. This unbiased approach revealed genes involved in cellular processes known to change with age, including mitochondrial function and meiotic chromosome segregation, but also uncovered previously unappreciated categories of genes related to proteostasis and organelles required for protein metabolism. We further validated our RNA-Seq data by comparing nucleolar structure and function in oocytes from reproductively young and old mice, as this organelle is central for protein production. We examined key nucleolar markers, including upstream binding transcription factor (UBTF), an RNA polymerase I cofactor, and fibrillarin, an rRNA methyltransferase. In oocytes from mice of advanced reproductive age, UBTF was primarily expressed in giant fibrillar centers (GFCs), structures associated with high levels of rDNA transcription, and fibrillarin expression was increased ~2-fold. At the ultrastructural level, oocyte nucleoli from reproductively old mice had correspondingly more prominent fibrillar centers and dense fibrillar centers relative to young controls and more ribosomes were found in the cytoplasm. Taken together, our findings are significant because the growing oocyte is one of the most translationally active cells in the body and must accumulate high-quality maternally derived proteins to support subsequent embryo development. Thus, perturbations in protein metabolism are likely to have a profound impact on gamete health.
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Affiliation(s)
- Francesca E. Duncan
- Department of Anatomy and Cell BiologyUniversity of Kansas Medical CenterKansas CityKS66160USA
- Present address:
Department of Obstetrics and GynecologyFeinberg School of MedicineNorthwestern UniversityChicagoIL60611,USA
| | - Susmita Jasti
- Department of Anatomy and Cell BiologyUniversity of Kansas Medical CenterKansas CityKS66160USA
| | - Ariel Paulson
- Stowers Institute for Medical ResearchKansas CityMO64110USA
| | - John M. Kelsh
- Department of Anatomy and Cell BiologyUniversity of Kansas Medical CenterKansas CityKS66160USA
| | - Barbara Fegley
- Department of Anatomy and Cell BiologyUniversity of Kansas Medical CenterKansas CityKS66160USA
- Electron Microscopy Research LaboratoryUniversity of Kansas Medical CenterKansas CityKS66160USA
| | - Jennifer L. Gerton
- Stowers Institute for Medical ResearchKansas CityMO64110USA
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKS66160USA
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Stępiński D. Functional ultrastructure of the plant nucleolus. PROTOPLASMA 2014; 251:1285-306. [PMID: 24756369 PMCID: PMC4209244 DOI: 10.1007/s00709-014-0648-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 04/08/2014] [Indexed: 05/23/2023]
Abstract
Nucleoli are nuclear domains present in almost all eukaryotic cells. They not only specialize in the production of ribosomal subunits but also play roles in many fundamental cellular activities. Concerning ribosome biosynthesis, particular stages of this process, i.e., ribosomal DNA transcription, primary RNA transcript processing, and ribosome assembly proceed in precisely defined nucleolar subdomains. Although eukaryotic nucleoli are conservative in respect of their main function, clear morphological differences between these structures can be noticed between individual kingdoms. In most cases, a plant nucleolus shows well-ordered structure in which four main ultrastructural components can be distinguished: fibrillar centers, dense fibrillar component, granular component, and nucleolar vacuoles. Nucleolar chromatin is an additional crucial structural component of this organelle. Nucleolonema, although it is not always an unequivocally distinguished nucleolar domain, has often been described as a well-grounded morphological element, especially of plant nucleoli. The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence. Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches. The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.
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Affiliation(s)
- Dariusz Stępiński
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland,
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Riancho J, Ruiz-Soto M, Villagrá NT, Berciano J, Berciano MT, Lafarga M. Compensatory Motor Neuron Response to Chromatolysis in the Murine hSOD1(G93A) Model of Amyotrophic Lateral Sclerosis. Front Cell Neurosci 2014; 8:346. [PMID: 25374511 PMCID: PMC4206191 DOI: 10.3389/fncel.2014.00346] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 10/06/2014] [Indexed: 11/13/2022] Open
Abstract
We investigated neuronal self-defense mechanisms in a murine model of amyotrophic lateral sclerosis (ALS), the transgenic hSOD1(G93A), during both the asymptomatic and symptomatic stages. This is an experimental model of endoplasmic reticulum (ER) stress with severe chromatolysis. As a compensatory response to translation inhibition, chromatolytic neurons tended to reorganize the protein synthesis machinery at the perinuclear region, preferentially at nuclear infolding domains enriched in nuclear pores. This organization could facilitate nucleo-cytoplasmic traffic of RNAs and proteins at translation sites. By electron microscopy analysis, we observed that the active euchromatin pattern and the reticulated nucleolar configuration of control motor neurons were preserved in ALS chromatolytic neurons. Moreover the 5'-fluorouridine (5'-FU) transcription assay, at the ultrastructural level, revealed high incorporation of the RNA precursor 5'-FU into nascent RNA. Immunogold particles of 5'-FU incorporation were distributed throughout the euchromatin and on the dense fibrillar component of the nucleolus in both control and ALS motor neurons. The high rate of rRNA transcription in ALS motor neurons could maintain ribosome biogenesis under conditions of severe dysfunction of proteostasis. Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis. In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases. Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.
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Affiliation(s)
- Javier Riancho
- Service of Neurology, University Hospital Marqués de Valdecilla, Instituto de Investigación Valdecilla (IDIVAL), University of Cantabria , Santander , Spain
| | - Maria Ruiz-Soto
- Department of Anatomy and Cell Biology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Instituto de Investigación Valdecilla, University of Cantabria , Santander , Spain
| | - Nuria T Villagrá
- Service of Pathology, University Hospital Marqués de Valdecilla, Instituto de Investigación Valdecilla, University of Cantabria , Santander , Spain
| | - Jose Berciano
- Service of Neurology, University Hospital Marqués de Valdecilla, Instituto de Investigación Valdecilla (IDIVAL), University of Cantabria , Santander , Spain
| | - Maria T Berciano
- Department of Anatomy and Cell Biology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Instituto de Investigación Valdecilla, University of Cantabria , Santander , Spain
| | - Miguel Lafarga
- Department of Anatomy and Cell Biology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Instituto de Investigación Valdecilla, University of Cantabria , Santander , Spain
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Palanca A, Casafont I, Berciano MT, Lafarga M. Reactive nucleolar and Cajal body responses to proteasome inhibition in sensory ganglion neurons. Biochim Biophys Acta Mol Basis Dis 2013; 1842:848-59. [PMID: 24269586 DOI: 10.1016/j.bbadis.2013.11.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 11/12/2013] [Accepted: 11/13/2013] [Indexed: 12/25/2022]
Abstract
The dysfunction of the ubiquitin proteasome system has been related to a broad array of neurodegenerative disorders in which the accumulation of misfolded protein aggregates causes proteotoxicity. The ability of proteasome inhibitors to induce cell cycle arrest and apoptosis has emerged as a powerful strategy for cancer therapy. Bortezomib is a proteasome inhibitor used as an antineoplastic drug, although its neurotoxicity frequently causes a severe sensory peripheral neuropathy. In this study we used a rat model of bortezomib treatment to study the nucleolar and Cajal body responses to the proteasome inhibition in sensory ganglion neurons that are major targets of bortezomib-induced neurotoxicity. Treatment with bortezomib induced dose-dependent dissociation of protein synthesis machinery (chromatolysis) and nuclear retention of poly(A) RNA granules resulting in neuronal dysfunction. However, as a compensatory response to the proteotoxic stress, both nucleoli and Cajal bodies exhibited reactive changes. These include an increase in the number and size of nucleoli, strong nucleolar incorporation of the RNA precursor 5'-fluorouridine, and increased expression of both 45S rRNA and genes encoding nucleolar proteins UBF, fibrillarin and B23. Taken together, these findings appear to reflect the activation of the nucleolar transcription in response to proteotoxic stress Furthermore, the number of Cajal bodies, a parameter related to transcriptional activity, increases upon proteasome inhibition. We propose that nucleoli and Cajal bodies are important targets in the signaling pathways that are activated by the proteotoxic stress response to proteasome inhibition. The coordinating activity of these two organelles in the production of snRNA, snoRNA and rRNA may contribute to neuronal survival after proteasome inhibition. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.
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Affiliation(s)
- Ana Palanca
- Department of Anatomy and Cell Biology, University of Cantabria-IFIMAV, Santander, Spain; "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", Santander, Spain
| | - Iñigo Casafont
- Department of Anatomy and Cell Biology, University of Cantabria-IFIMAV, Santander, Spain; "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", Santander, Spain
| | - María T Berciano
- Department of Anatomy and Cell Biology, University of Cantabria-IFIMAV, Santander, Spain; "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", Santander, Spain
| | - Miguel Lafarga
- Department of Anatomy and Cell Biology, University of Cantabria-IFIMAV, Santander, Spain; "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", Santander, Spain.
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Hwang YJ, Han D, Kim KY, Min SJ, Kowall NW, Yang L, Lee J, Kim Y, Ryu H. ESET methylates UBF at K232/254 and regulates nucleolar heterochromatin plasticity and rDNA transcription. Nucleic Acids Res 2013; 42:1628-43. [PMID: 24234436 PMCID: PMC3919562 DOI: 10.1093/nar/gkt1041] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The remodeling of chromatin in the nucleolus is important for the control of ribosomal DNA (rDNA) transcription and ribosome biogenesis. Herein, we found that upstream binding factor (UBF) interacts with ESET, a histone H3K9 methyltransferase and is trimethylated at Lys (K) 232/254 by ESET. UBF trimethylation leads to nucleolar chromatin condensation and decreased rDNA transcriptional activity. UBF mutations at K232/254A and K232/254R restored rDNA transcriptional activity in response to ESET. Both ESET-ΔSET mutant and knockdown of ESET by short hairpin RNA reduced trimethylation of UBF and resulted in the restoration of rDNA transcription. Atomic force microscopy confirmed that UBF trimethylated by ESET modulates the plasticity of nucleolar chromatin. We further demonstrated that UBF trimethylation at K232/254 by ESET deregulates rDNA transcription in a cell model of Huntington’s disease. Together, our findings show that a novel epigenetic modification of UBF is linked to impaired rDNA transcription and nucleolar chromatin remodeling, which may play key roles in the pathogenesis of neurodegeneration.
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Affiliation(s)
- Yu Jin Hwang
- Department of Biomedical Sciences, World Class University Neurocytomics Group, Seoul National University College of Medicine, Seoul 110-799, South Korea, Medical Engineering, Seoul National University College of Medicine, Seoul 110-799, South Korea, Center for Neuro-Medicine, Brain Science Institute, Korea Institute of Science and Technology (KIST), Seoul 136-791, South Korea, VA Boston Healthcare System, Boston, MA 02130, USA, Boston University Alzheimer's Disease Center and Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA, Department of Orthopedics and Division of Hematology, University of Washington School of Medicine, Seattle, WA 98195, USA and Medical Research Service, VA Puget Sound Health Care System, Seattle, WA 98108, USA
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Lee J, Hwang YJ, Ryu H, Kowall NW, Ryu H. Nucleolar dysfunction in Huntington's disease. Biochim Biophys Acta Mol Basis Dis 2013; 1842:785-90. [PMID: 24184605 DOI: 10.1016/j.bbadis.2013.09.017] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 09/27/2013] [Indexed: 01/17/2023]
Abstract
Huntington's disease (HD) is a fatal genetic disorder characterized by triad clinical symptoms of chorea, emotional distress, and cognitive decline. Genetic mutation in HD is identified by an expansion of CAG repeats coding for glutamine (Q) in exon 1 of the huntingtin (htt) gene. The exact mechanism on how mutant htt leads to the selective loss of medium spiny neurons (MSNs) in the striatum is still unknown. Recent studies suggest that nucleolar stress and dysfunction are linked to the pathogenesis of HD. Alterations of the nucleolar activity and integrity contribute to deregulation of ribosomal DNA (rDNA) transcription in HD pathogenesis. Furthermore, epigenetic modifications in the nucleolus are associated with neuronal damage in HD. In this review, we discuss about how post-translational modifications of upstream binding factor (UBF) are affected by histone acetyltransferase and histone methyltransferase and involved in the transcriptional regulation of rDNA in HD. The understanding of epigenetic modulation of UBF-dependent rDNA transcription in the nucleolus may lead to the identification of novel pathological markers and new therapeutic targets to treat HD. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.
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Affiliation(s)
- Junghee Lee
- VA Boston Healthcare System, Boston, MA 02130, USA; Boston University, Alzheimer's Disease Center, Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA
| | - Yu Jin Hwang
- WCU Neurocytomics Group, Department of Biomedical Sciences, Seoul National University Graduate School, Seoul 110-799, South Korea
| | - Hyun Ryu
- Boston University, Alzheimer's Disease Center, Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA
| | - Neil W Kowall
- VA Boston Healthcare System, Boston, MA 02130, USA; Boston University, Alzheimer's Disease Center, Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA
| | - Hoon Ryu
- VA Boston Healthcare System, Boston, MA 02130, USA; Boston University, Alzheimer's Disease Center, Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA; Center for Neuro-Medicine, Brain Science Institute, Korea Institute of Science and Technology, Seoul, South Korea.
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10
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Wang F, Ying C, Shang G, Jiao M, Hongfang Z. The new evidence of nucleolar ultrastructural dynamic change: fibrillar centre (FC) fusion in G1 phase and regeneration in S phase. Micron 2013; 49:15-20. [PMID: 23602556 DOI: 10.1016/j.micron.2013.02.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 02/12/2013] [Accepted: 02/21/2013] [Indexed: 01/15/2023]
Abstract
In higher eukaryotes ribosome production starts at the end of mitosis, increases during G1, is maximal in G2 (Sirri et al., 2000) and stops during prophase (Gébrane-Younès et al., 1997). But the mechanism of the change is still uncovered. Especially in the actively growing mammalian somatic cells usually contain one or several giant fibrillar centres (GFCs) with many tiny fibrillar centre (FCs) (Koberna et al., 2002; Raška et al., 2004; Casafont et al., 2007). The process how the giant fibrillar centre (GFC) and the many tiny fibrillar centres (FCs) were formed is unknown. The present results showed there were processes of FCs fusion in G1 phase and FCs regeneration in S phase respectively in the nucleoli of A 375 cells. A few FCs fused each other in late G1 phase when the process of nucleoli fusion was completed. In S phase, a lot of tiny FCs were regenerated from the periphery of GFC, separated and scattered into nucleolar matrix in late S phase and early G2 phase. The GFC was found to be coexisted with numerous tiny FCs in the nucleolus in G2 phase. The present study provided a new evidence of nucleolar dynamic change during interphase: fibrillar centre (FC) was not to be a stable state subunit of nucleolar compartment but a highly dynamic process that may be the bases of nucleolar morphological architecture organization and its function taking place.
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Affiliation(s)
- Fengcai Wang
- Jiu Jiang University, Jiangxi Province 332000, China
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11
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Abstract
As the most prominent sub-nuclear compartment in the interphase nucleus and the site of ribosome biogenesis, the nucleolus synthesizes and processes rRNA and also assembles ribosomal subunits. Though several lines of research in recent years have indicated that the nucleolus might have additional functions-such as the assembling of signal recognition particles, the processing of mRNA, tRNA and telomerase activities, and regulating the cell cycle-proteomic analyses of the nucleolus in three representative eukaryotic species has shown that a plethora of proteins either have no association with ribosome biogenesis or are of presently unknown function. This phenomenon further indicates that the composition and function of the nucleolus is far more complicated than previously thought. Meanwhile, the available nucleolar proteome databases has provided new approaches and led to remarkable progress in understanding the nucleolus. Here, we have summarized recent advances in the study of the nucleolus, including new discoveries of its structure, function, genomics/proteomics as well as its origin and evolution. Moreover, we highlight several of the important unresolved issues in this field.
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Abstract
The nucleolus is a distinct subnuclear compartment known as the site for ribosome biogenesis in eukaryotes. Consequently, the nucleolus is also proposed to function in cell-cycle control, stress sensing and senescence, as well as in viral infection. An increasing number of viral proteins have been found to localize to the nucleolus. In this article, we review the current understanding of the functions of the nucleolus, the molecular mechanism of cellular and viral protein targeting to the nucleolus and the functional roles of the nucleolus during viral infection with a specific focus on the herpesvirus family.
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Affiliation(s)
- Liwen Ni
- Molecular Virology and Viral Immunology Research Group, State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, PR China
| | - Shuai Wang
- Molecular Virology and Viral Immunology Research Group, State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, PR China
| | - Chunfu Zheng
- Molecular Virology and Viral Immunology Research Group, State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, PR China
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Torres-Montaner A, Huq M. Histopathological study comparing upstream binding factor expression and AgNOR staining. Cell Prolif 2012; 45:345-51. [PMID: 22731742 DOI: 10.1111/j.1365-2184.2012.00829.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
AgNOR staining has been in past years, the subject of numerous publications, which have failed to reach agreement regarding its usefulness as a proliferation marker. This silver staining method does not react with NORs (actual chromosome regions containing rRNA (ribosomal RNA) genes), but with proteins associated with them, whose quantity increases in parallel with ribosome biogenesis. The transcription factor UBF (upstream binding factor) is associated with NORs and has an important regulatory role in rRNA synthesis as cofactor of RNA polymerase I. Recent research has revealed an additional cytoarchitectural function of UBF in decondensing r-chromatin (ribosomal-chromatin). Immune detection of UBF expression and AgNOR counts are closely correlated as both techniques identify substrates in or closely adjacent to NORs. However, contrary to AgNOR dots, the UBF signal disappears in cells which undergo apoptosis or terminal differentiation. These features imply that UBF evaluation would reflect tumour cell proliferation (growth fraction) more accurately than AgNOR counts. Here we also show that immunohistochemical staining of UBF may reveal distinct active NORs with open, decondensed chromatin and we hypothesize that the large stretches of decondensed r-chromatin revealed by UBF staining may correspond to clusters seen after silver staining and, conversely, shorter areas of decondensed r-chromatin should match the small AgNOR grains typically found in some tumour types. The length of decondensed r-chromatin may be a reflection of the ratio of active to silent r-RNA genes.
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14
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Hetman M, Pietrzak M. Emerging roles of the neuronal nucleolus. Trends Neurosci 2012; 35:305-14. [PMID: 22305768 DOI: 10.1016/j.tins.2012.01.002] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Revised: 12/15/2011] [Accepted: 01/03/2012] [Indexed: 12/22/2022]
Abstract
Although, the nucleolus has been observed for almost 200 years in neurons, studies that directly address the neuronal roles of this subnuclear structure have appeared only recently. The aim of this review is to discuss recent progress and identify some critical questions that remain to be answered. As expected for the cellular center of ribosome biogenesis, the nucleolus is essential for the growth of developing neurons, including neurite morphogenesis and long-term maintenance of mature neurons. In addition, the nucleolus contributes to neuronal stress responses, including the regulation of apoptosis. Hence, disrupted neurodevelopment or neurodegeneration are among the likely consequences of nucleolar dysfunction. Conversely, the presence of active nucleoli may determine the potential for neurorepair.
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Affiliation(s)
- Michal Hetman
- Kentucky Spinal Cord Injury Research Center and Department of Neurological Surgery, University of Louisville, Louisville, Kentucky 40292, USA.
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15
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Diffuse traumatic axonal injury in the mouse induces atrophy, c-Jun activation, and axonal outgrowth in the axotomized neuronal population. J Neurosci 2011; 31:5089-105. [PMID: 21451046 DOI: 10.1523/jneurosci.5103-10.2011] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI) and is associated with much of its morbidity. Little is known regarding the long-term retrograde neuronal consequences of TAI and/or the potential that TAI could lead to anterograde axonal reorganization and repair. To investigate the repertoire of anterograde and retrograde responses triggered by TIA, Thy1-YFP-H mice were subjected to mild central fluid percussion injury and killed at various times between 15 min and 28 d post-injury. Based upon confocal assessment of the endogenous neuronal fluorescence, such injury was found to result in diffuse TAI throughout layer V of the neocortex within yellow fluorescent protein (YFP)-positive axons. When these fluorescent approaches were coupled with various quantitative and immunohistochemical approaches, we found that this TAI did not result in neuronal death over the 28 d period assessed. Rather, it elicited neuronal atrophy. Within these same axotomized neuronal populations, TAI was also found to induce an early and sustained activation of the transcription factors c-Jun and ATF-3 (activating transcription factor 3), known regulators of axon regeneration. Parallel ultrastructural studies confirmed that these reactive changes are consistent with atrophy in the absence of neuronal death. Concurrent with those events ongoing in the neuronal cell bodies, their downstream axonal segments revealed, as early as 1 d post-injury, morphological changes consistent with reactive sprouting that was accompanied by significant axonal elongation over time. Collectively, these TAI-linked events are consistent with sustained neuronal recovery, an activation of a regenerative genetic program, and subsequent axonal reorganization suggestive of some form of regenerative response.
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16
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Dysregulation of upstream binding factor-1 acetylation at K352 is linked to impaired ribosomal DNA transcription in Huntington's disease. Cell Death Differ 2011; 18:1726-35. [PMID: 21546905 DOI: 10.1038/cdd.2011.38] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Huntington's disease (HD) is an autosomal-dominant neurological disorder caused by expanded CAG repeats in the Huntingtin (Htt) gene, but it is not known how this mutation causes neurodegeneration. Herein, we found that dysfunction of upstream binding factor-1 (UBF-1) is linked to reduced ribosomal DNA (rDNA) transcription in HD. We identified that UBF1 acetylation at Lys (K) 352 by CREB binding protein (CBP) is crucial for the transcriptional activity of rDNA. UBF1 mutation (K352A, K352Q, and K352R) decreased rDNA transcriptional activity. Moreover, both CBP-dHAT mutant and knockdown of CBP by siRNA reduced acetylation of UBF1 and resulted in the decreased transcription of rDNA into rRNA. ChIP analysis showed a significant reduction of UBF1 occupancy in the promoter of rDNA in STHdh(Q111) cell line model of HD. These results demonstrate that abnormal activity of UBF1 and its acetylation by CBP are linked to impaired rDNA transcription in HD. This novel mechanism suggests that modulation of UBF-mediated rDNA synthesis by CBP may be a therapeutic target for improving neuronal rDNA transcription in HD.
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Baltanás FC, Casafont I, Weruaga E, Alonso JR, Berciano MT, Lafarga M. Nucleolar disruption and cajal body disassembly are nuclear hallmarks of DNA damage-induced neurodegeneration in purkinje cells. Brain Pathol 2010; 21:374-88. [PMID: 21054627 DOI: 10.1111/j.1750-3639.2010.00461.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The Purkinje cell (PC) degeneration (pcd) phenotype results from mutation in nna1 gene and is associated with the degeneration and death of PCs during the postnatal life. Although the pcd mutation is a model of the ataxic mouse, it shares clinical and pathological characteristics of inherited human spinocerebellar ataxias. PC degeneration in pcd mice provides a useful neuronal system to study nuclear mechanisms involved in DNA damage-dependent neurodegeneration, particularly the contribution of nucleoli and Cajal bodies (CBs). Both nuclear structures are engaged in housekeeping functions for neuronal survival, the biogenesis of ribosomes and the maturation of snRNPs and snoRNPs required for pre-mRNA and pre-rRNA processing, respectively. In this study, we use ultrastructural analysis, in situ transcription assay and molecular markers for DNA damage, nucleoli and CB components to demonstrate that PC degeneration involves the progressive accumulation of nuclear DNA damage associated with disruption of nucleoli and CBs, disassembly of polyribosomes into monoribosomes, ribophagy and shut down of nucleolar and extranucleolar transcription. Microarray analysis reveals that four genes encoding repressors of nucleolar rRNA synthesis (p53, Rb, PTEN and SNF2) are upregulated in the cerebellum of pcd mice. Collectively, these data support that nucleolar and CB alterations are hallmarks of DNA damage-induced neurodegeneration.
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Affiliation(s)
- Fernando C Baltanás
- Laboratory of Neural Plasticity and Neurorepair, Institute for Neuroscience of Castilla y León, Universidad de Salamanca, Salamanca, Spain
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18
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Hernandez-Verdun D, Roussel P, Thiry M, Sirri V, Lafontaine DLJ. The nucleolus: structure/function relationship in RNA metabolism. WILEY INTERDISCIPLINARY REVIEWS-RNA 2010; 1:415-31. [PMID: 21956940 DOI: 10.1002/wrna.39] [Citation(s) in RCA: 176] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The nucleolus is the ribosome factory of the cells. This is the nuclear domain where ribosomal RNAs are synthesized, processed, and assembled with ribosomal proteins. Here we describe the classical tripartite organization of the nucleolus in mammals, reflecting ribosomal gene transcription and pre-ribosomal RNA (pre-rRNA) processing efficiency: fibrillar center, dense fibrillar component, and granular component. We review the nucleolar organization across evolution from the bipartite organization in yeast to the tripartite organization in humans. We discuss the basic principles of nucleolar assembly and nucleolar structure/function relationship in RNA metabolism. The control of nucleolar assembly is presented as well as the role of pre-existing machineries and pre-rRNAs inherited from the previous cell cycle. In addition, nucleoli carry many essential extra ribosomal functions and are closely linked to cellular homeostasis and human health. The last part of this review presents recent advances in nucleolar dysfunctions in human pathology such as cancer and virus infections that modify the nucleolar organization.
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Affiliation(s)
- Danièle Hernandez-Verdun
- Nuclei and cell cycle, Institut Jacques Monod-UMR 7592 CNRS, Université Paris Diderot, 75205 Paris cedex 13, France.
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19
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Richendrfer HA, Swann JM. Neuronal composition of the magnocellular division of the medial preoptic nucleus (MPN mag) is sex specific in the Syrian hamster (Mesocricetus auratus). Brain Res 2010; 1351:97-103. [PMID: 20615396 DOI: 10.1016/j.brainres.2010.06.068] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Revised: 06/26/2010] [Accepted: 06/29/2010] [Indexed: 10/19/2022]
Abstract
The magnocellular division of the medial Preoptic nucleus (MPN mag) plays a critical role in the regulation of male sexual behavior in the hamster. Results from previous studies indicated that the number of neurons in the MPN mag is greater in males than females but failed to find significant differences in the volume of the nucleus suggesting that other elements in the nucleus may be greater in the female. The results of the present study, using NeuN to identify neurons, are in line with this hypothesis. The data show that (1) neurons in the MPN mag display two distinct phenotypes, those with a single nucleolus and those with multiple nucleoli; (2) the percentage of each phenotype is sex specific, differing over the course of development and (3) there is no sex difference in the number of glial cells at any age. Sex differences in the numbers of each type are correlated with developmental milestones and suggest that morphological changes are influenced by changes in circulating gonadal steroids during development.
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Affiliation(s)
| | - Jennifer M Swann
- Lehigh University, Department of Biological Sciences, Bethlehem, PA, USA.
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20
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Stepiński D. Organization of the nucleoli of soybean root meristematic cells at different states of their activity. Micron 2010; 41:283-8. [PMID: 20071186 DOI: 10.1016/j.micron.2009.11.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 11/23/2009] [Accepted: 11/25/2009] [Indexed: 10/20/2022]
Abstract
Internal organization of a nucleolus changes along with rRNA transcriptional activity. These changes mainly concern qualitative and quantitative alternations of three main nucleolar components: fibrillar centres (FC), dense fibrillar component (DFC) and granular component (GC). In the present work quantitative measurements of the number and sizes of FCs and DFCs in nucleoli of root meristematic cells of soybean seedlings grown at (1) chilling conditions that reduce transcriptional activity of soybean nucleoli (temp. of 10 degrees C) and at (2) conditions that increase this activity (recovery at optimal temp. of 25 degrees C after previous chilling), even more than (3) the control, have been carried out. Morphometric measurements showed that the highest number of FCs and DFCs was in the most active nucleoli, while the smallest number - in those with the lowest activity. The average size of an individual FC was similar in all nucleoli regardless of their transcriptional activity, that of the individual DFC varied, being bigger in the nucleoli of the chilled plants and smallest in those of the recovered plants. The numbers of FCs and DFCs seem to be indicators of transcriptional activity of plant nucleoli - the higher number of FCs and DFCs the more active nucleoli.
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Affiliation(s)
- Dariusz Stepiński
- Department of Cytophysiology, University of Łódź, Pilarskiego 14, 90-321 Łódź, Poland.
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Cisterna B, Biggiogera M. Ribosome biogenesis: from structure to dynamics. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2010; 284:67-111. [PMID: 20875629 DOI: 10.1016/s1937-6448(10)84002-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In this chapter we describe the status of the research concerning the nucleolus, the major nuclear body. The nucleolus has been recognized as a dynamic organelle with many more functions than one could imagine. In fact, in addition to its fundamental role in the biogenesis of preribosomes, the nucleolus takes part in many other cellular processes and functions, such as the cell-cycle control and the p53 pathway: the direct or indirect involvement of the nucleolus in these various processes makes it sensitive to their alteration. Moreover, it is worth noting that the different nucleolar factors participating to independent mechanisms show different dynamics of association/disassociation with the nucleolar body.
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Affiliation(s)
- Barbara Cisterna
- Laboratory of Cell Biology and Neurobiology, Department of Animal Biology, University of Pavia, Pavia, Italy
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22
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Karni-Schmidt O, Zupnick A, Castillo M, Ahmed A, Matos T, Bouvet P, Cordon-Cardo C, Prives C. p53 is localized to a sub-nucleolar compartment after proteasomal inhibition in an energy-dependent manner. J Cell Sci 2008; 121:4098-105. [PMID: 19033390 DOI: 10.1242/jcs.030098] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The tumor suppressor p53 is activated in response to many forms of cellular stress leading to cell cycle arrest, senescence or apoptosis. Appropriate sub-cellular localization is essential for modulating p53 function. We recently showed that p53 localizes to the nucleolus after proteasome inhibition with MG132 and this localization requires sequences within its carboxyl terminus. In the present study, we found that after treatment with MG132, p53 associates with a discrete sub-nucleolar component, the fibrillar center (FC), a region mainly enriched with RNA polymerase I. Moreover, we now demonstrate that this localization is an energy-dependent process as reduction of ATP levels prevents nucleolar localization. In addition, p53 sub-nucleolar accumulation is abolished when cells are subjected to various types of genotoxic stress. Furthermore, we show that monoubiquitination of p53, which causes it to localize to the cytoplasm and nucleoplasm, does not prevent the association of p53 with the nucleolus after MG132 treatment. Importantly, we demonstrate that p53 nucleolar association occurs in lung and bladder carcinomas.
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Affiliation(s)
- Orit Karni-Schmidt
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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23
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State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology. Histochem Cell Biol 2008; 130:1205-51. [PMID: 18985372 DOI: 10.1007/s00418-008-0535-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/21/2008] [Indexed: 10/25/2022]
Abstract
Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.
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Sirri V, Urcuqui-Inchima S, Roussel P, Hernandez-Verdun D. Nucleolus: the fascinating nuclear body. Histochem Cell Biol 2007; 129:13-31. [PMID: 18046571 PMCID: PMC2137947 DOI: 10.1007/s00418-007-0359-6] [Citation(s) in RCA: 295] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/06/2007] [Indexed: 11/30/2022]
Abstract
Nucleoli are the prominent contrasted structures of the cell nucleus. In the nucleolus, ribosomal RNAs are synthesized, processed and assembled with ribosomal proteins. RNA polymerase I synthesizes the ribosomal RNAs and this activity is cell cycle regulated. The nucleolus reveals the functional organization of the nucleus in which the compartmentation of the different steps of ribosome biogenesis is observed whereas the nucleolar machineries are in permanent exchange with the nucleoplasm and other nuclear bodies. After mitosis, nucleolar assembly is a time and space regulated process controlled by the cell cycle. In addition, by generating a large volume in the nucleus with apparently no RNA polymerase II activity, the nucleolus creates a domain of retention/sequestration of molecules normally active outside the nucleolus. Viruses interact with the nucleolus and recruit nucleolar proteins to facilitate virus replication. The nucleolus is also a sensor of stress due to the redistribution of the ribosomal proteins in the nucleoplasm by nucleolus disruption. The nucleolus plays several crucial functions in the nucleus: in addition to its function as ribosome factory of the cells it is a multifunctional nuclear domain, and nucleolar activity is linked with several pathologies. Perspectives on the evolution of this research area are proposed.
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Affiliation(s)
- Valentina Sirri
- Nuclei and Cell Cycle, CNRS, Université Paris VI, Université Paris VII, Institut Jacques Monod, 2 place Jussieu, 75251 Paris Cedex 05, France
| | - Silvio Urcuqui-Inchima
- Nuclei and Cell Cycle, CNRS, Université Paris VI, Université Paris VII, Institut Jacques Monod, 2 place Jussieu, 75251 Paris Cedex 05, France
- Grupo de Inmunovirología, Biogénesis, Universidad de Antioquia, Calle 62 No. 52-59, Medellin, Colombia
| | - Pascal Roussel
- Nuclei and Cell Cycle, CNRS, Université Paris VI, Université Paris VII, Institut Jacques Monod, 2 place Jussieu, 75251 Paris Cedex 05, France
| | - Danièle Hernandez-Verdun
- Nuclei and Cell Cycle, CNRS, Université Paris VI, Université Paris VII, Institut Jacques Monod, 2 place Jussieu, 75251 Paris Cedex 05, France
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