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Delourme M, Charlene C, Gerard L, Ganne B, Perrin P, Vovan C, Bertaux K, Nguyen K, Bernard R, Magdinier F. Complex 4q35 and 10q26 Rearrangements: A Challenge for Molecular Diagnosis of Patients With Facioscapulohumeral Dystrophy. Neurol Genet 2023; 9:e200076. [PMID: 37200893 PMCID: PMC10188231 DOI: 10.1212/nxg.0000000000200076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 03/23/2023] [Indexed: 05/20/2023]
Abstract
Background and Objectives After clinical evaluation, the molecular diagnosis of type 1 facioscapulohumeral dystrophy (FSHD1) relies in most laboratories on the detection of a shortened D4Z4 array at the 4q35 locus by Southern blotting. In many instances, this molecular diagnosis remains inconclusive and requires additional experiments to determine the number of D4Z4 units or identify somatic mosaicism, 4q-10q translocations, and proximal p13E-11 deletions. These limitations highlight the need for alternative methodologies, illustrated by the recent emergence of novel technologies such as molecular combing (MC), single molecule optical mapping (SMOM), or Oxford Nanopore-based long-read sequencing providing a more comprehensive analysis of 4q and 10q loci. Over the last decade, MC revealed a further increasing complexity in the organization of the 4q and 10q distal regions in patients with FSHD with cis-duplication of D4Z4 arrays in approximately 1%-2% of cases. Methods By using MC, we investigated in our center 2,363 cases for molecular diagnosis of FSHD. We also evaluated whether previously reported cis-duplications might be identified by SMOM using the Bionano EnFocus FSHD 1.0 algorithm. Results In our cohort of 2,363 samples, we identified 147 individuals carrying an atypical organization of the 4q35 or 10q26 loci. Mosaicism is the most frequent category followed by cis-duplications of the D4Z4 array. We report here chromosomal abnormalities of the 4q35 or 10q26 loci in 54 patients clinically described as FSHD, which are not present in the healthy population. In one-third of the 54 patients, these rearrangements are the only genetic defect suggesting that they might be causative of the disease. By analyzing DNA samples from 3 patients carrying a complex rearrangement of the 4q35 region, we further showed that the SMOM direct assembly of the 4q and 10q alleles failed to reveal these abnormalities and lead to negative results for FSHD molecular diagnosis. Discussion This work further highlights the complexity of the 4q and 10q subtelomeric regions and the need of in-depth analyses in a significant number of cases. This work also highlights the complexity of the 4q35 region and interpretation issues with consequences on the molecular diagnosis of patients or genetic counseling.
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Affiliation(s)
- Megane Delourme
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Chaix Charlene
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Laurene Gerard
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Benjamin Ganne
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Pierre Perrin
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Catherine Vovan
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Karine Bertaux
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Karine Nguyen
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Rafaëlle Bernard
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
| | - Frederique Magdinier
- From the Aix Marseille University (M.D., B.G., P.P., K.N., R.B., F.M.), INSERM; Département de Génétique Médicale (C.C., L.G., C.V., K.B., K.N., R.B.), and Centre de Ressources Biologiques (K.B.), AP-HM, Hôpital d'enfants de la Timone, Marseille, France
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2
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Rang FJ, Kind J, Guerreiro I. The role of heterochromatin in 3D genome organization during preimplantation development. Cell Rep 2023; 42:112248. [PMID: 37059092 DOI: 10.1016/j.celrep.2023.112248] [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: 08/15/2022] [Revised: 12/21/2022] [Accepted: 02/27/2023] [Indexed: 04/16/2023] Open
Abstract
During the early stages of mammalian development, the epigenetic state of the parental genome is completely reprogrammed to give rise to the totipotent embryo. An important aspect of this remodeling concerns the heterochromatin and the spatial organization of the genome. While heterochromatin and genome organization are intricately linked in pluripotent and somatic systems, little is known about their relationship in the totipotent embryo. In this review, we summarize the current knowledge on the reprogramming of both regulatory layers. In addition, we discuss available evidence on their relationship and put this in the context of findings in other systems.
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Affiliation(s)
- Franka J Rang
- Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT Utrecht, the Netherlands; Oncode Institute, the Netherlands
| | - Jop Kind
- Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT Utrecht, the Netherlands; Oncode Institute, the Netherlands; Department of Molecular Biology, Faculty of Science, Radboud Institute for Molecular Life Sciences, Radboud University Nijmegen, Houtlaan 4, 6525 XZ Nijmegen, the Netherlands.
| | - Isabel Guerreiro
- Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center Utrecht, Uppsalalaan 8, 3584 CT Utrecht, the Netherlands; Oncode Institute, the Netherlands.
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3
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Pennarun G, Picotto J, Bertrand P. Close Ties between the Nuclear Envelope and Mammalian Telomeres: Give Me Shelter. Genes (Basel) 2023; 14:genes14040775. [PMID: 37107534 PMCID: PMC10137478 DOI: 10.3390/genes14040775] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 03/18/2023] [Accepted: 03/20/2023] [Indexed: 04/29/2023] Open
Abstract
The nuclear envelope (NE) in eukaryotic cells is essential to provide a protective compartment for the genome. Beside its role in connecting the nucleus with the cytoplasm, the NE has numerous important functions including chromatin organization, DNA replication and repair. NE alterations have been linked to different human diseases, such as laminopathies, and are a hallmark of cancer cells. Telomeres, the ends of eukaryotic chromosomes, are crucial for preserving genome stability. Their maintenance involves specific telomeric proteins, repair proteins and several additional factors, including NE proteins. Links between telomere maintenance and the NE have been well established in yeast, in which telomere tethering to the NE is critical for their preservation and beyond. For a long time, in mammalian cells, except during meiosis, telomeres were thought to be randomly localized throughout the nucleus, but recent advances have uncovered close ties between mammalian telomeres and the NE that play important roles for maintaining genome integrity. In this review, we will summarize these connections, with a special focus on telomere dynamics and the nuclear lamina, one of the main NE components, and discuss the evolutionary conservation of these mechanisms.
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Affiliation(s)
- Gaëlle Pennarun
- Université Paris Cité, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
- Université Paris-Saclay, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
| | - Julien Picotto
- Université Paris Cité, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
- Université Paris-Saclay, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
| | - Pascale Bertrand
- Université Paris Cité, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
- Université Paris-Saclay, INSERM, CEA, Stabilité Génétique Cellules Souches et Radiations, LREV/iRCM/IBFJ, F-92260 Fontenay-aux-Roses, France
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4
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Kychygina A, Dall'Osto M, Allen JAM, Cadoret JC, Piras V, Pickett HA, Crabbe L. Progerin impairs 3D genome organization and induces fragile telomeres by limiting the dNTP pools. Sci Rep 2021; 11:13195. [PMID: 34162976 PMCID: PMC8222272 DOI: 10.1038/s41598-021-92631-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 06/11/2021] [Indexed: 11/09/2022] Open
Abstract
Chromatin organization within the nuclear volume is essential to regulate many aspects of its function and to safeguard its integrity. A key player in this spatial scattering of chromosomes is the nuclear envelope (NE). The NE tethers large chromatin domains through interaction with the nuclear lamina and other associated proteins. This organization is perturbed in cells from Hutchinson–Gilford progeria syndrome (HGPS), a genetic disorder characterized by premature aging features. Here, we show that HGPS-related lamina defects trigger an altered 3D telomere organization with increased contact sites between telomeres and the nuclear lamina, and an altered telomeric chromatin state. The genome-wide replication timing signature of these cells is perturbed, with a shift to earlier replication for regions that normally replicate late. As a consequence, we detected a higher density of replication forks traveling simultaneously on DNA fibers, which relies on limiting cellular dNTP pools to support processive DNA synthesis. Remarkably, increasing dNTP levels in HGPS cells rescued fragile telomeres, and improved the replicative capacity of the cells. Our work highlights a functional connection between NE dysfunction and telomere homeostasis in the context of premature aging.
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Affiliation(s)
- Anna Kychygina
- Molecular, Cellular and Developmental Biology Department (MCD), Centre de Biologie Integrative (CBI), CNRS, UPS, University of Toulouse, 31062, Toulouse, France.,INSERM UMR1291, CNRS UMR5051, UT3, Toulouse Institute for Infectious and Inflammatory Diseases (Infinity), 31059, Toulouse, France
| | - Marina Dall'Osto
- Molecular, Cellular and Developmental Biology Department (MCD), Centre de Biologie Integrative (CBI), CNRS, UPS, University of Toulouse, 31062, Toulouse, France
| | - Joshua A M Allen
- Telomere Length Regulation Unit, Faculty of Medicine and Health, Children's Medical Research Institute, University of Sydney, Westmead, NSW, 2145, Australia
| | | | - Vincent Piras
- Molecular, Cellular and Developmental Biology Department (MCD), Centre de Biologie Integrative (CBI), CNRS, UPS, University of Toulouse, 31062, Toulouse, France
| | - Hilda A Pickett
- Telomere Length Regulation Unit, Faculty of Medicine and Health, Children's Medical Research Institute, University of Sydney, Westmead, NSW, 2145, Australia
| | - Laure Crabbe
- Molecular, Cellular and Developmental Biology Department (MCD), Centre de Biologie Integrative (CBI), CNRS, UPS, University of Toulouse, 31062, Toulouse, France.
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Abstract
Neuromuscular disorders are a heterogeneous group of conditions affecting the neuromuscular system. The aim of this article is to review the major epigenetic findings in motor neuron diseases and major hereditary muscular dystrophies. DNA methylation changes are observed in both hereditary and sporadic forms, and combining DNA methylation analysis with mutational screening holds the potential for better diagnostic and prognostic accuracy. Novel, less toxic and more selective epigenetic drugs are designed and tested in animal and cell culture models of neuromuscular disorders, and non-coding RNAs are being investigated as either disease biomarkers or targets of therapeutic approaches to restore gene expression levels. Overall, neuromuscular disorder epigenetic biomarkers have a strong potential for clinical applications in the near future.
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Affiliation(s)
- Fabio Coppedè
- Department of Translational Research & of New Surgical & Medical Technologies, University of Pisa, Via Roma 55, 56126 Pisa, Italy
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6
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Kwapisz M, Morillon A. Subtelomeric Transcription and its Regulation. J Mol Biol 2020; 432:4199-4219. [PMID: 32035903 PMCID: PMC7374410 DOI: 10.1016/j.jmb.2020.01.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 01/14/2020] [Accepted: 01/14/2020] [Indexed: 12/13/2022]
Abstract
The subtelomeres, highly heterogeneous repeated sequences neighboring telomeres, are transcribed into coding and noncoding RNAs in a variety of organisms. Telomereproximal subtelomeric regions produce non-coding transcripts i.e., ARRET, αARRET, subTERRA, and TERRA, which function in telomere maintenance. The role and molecular mechanisms of the majority of subtelomeric transcripts remain unknown. This review depicts the current knowledge and puts into perspective the results obtained in different models from yeasts to humans.
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Affiliation(s)
- Marta Kwapisz
- Laboratoire de Biologie Moléculaire Eucaryote, Centre de Biologie Intégrative (CBI), Université de Toulouse, CNRS, UPS, France
| | - Antonin Morillon
- ncRNA, Epigenetic and Genome Fluidity, CNRS UMR 3244, Sorbonne Université, PSL University, Institut Curie, Centre de Recherche, 26 rue d'Ulm, 75248, Paris, France.
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7
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Gaillard MC, Broucqsault N, Morere J, Laberthonnière C, Dion C, Badja C, Roche S, Nguyen K, Magdinier F, Robin JD. Analysis of the 4q35 chromatin organization reveals distinct long-range interactions in patients affected with Facio-Scapulo-Humeral Dystrophy. Sci Rep 2019; 9:10327. [PMID: 31316120 PMCID: PMC6637155 DOI: 10.1038/s41598-019-46861-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Accepted: 06/25/2019] [Indexed: 12/15/2022] Open
Abstract
Facio-Scapulo Humeral dystrophy (FSHD) is the third most common myopathy, affecting 1 amongst 10,000 individuals (FSHD1, OMIM #158900). This autosomal dominant pathology is associated in 95% of cases with genetic and epigenetic alterations in the subtelomeric region at the extremity of the long arm of chromosome 4 (q arm). A large proportion of the remaining 5% of cases carry a mutation in the SMCHD1 gene (FSHD2, OMIM #158901). Here, we explored the 3D organization of the 4q35 locus by three-dimensions DNA in situ fluorescent hybridization (3D-FISH) in primary fibroblasts isolated from patients and healthy donors. We found that D4Z4 contractions and/or SMCHD1 mutations impact the spatial organization of the 4q35 region and trigger changes in the expression of different genes. Changes in gene expression were corroborated in muscle biopsies suggesting that the modified chromatin landscape impelled a modulation in the level of expression of a number of genes across the 4q35 locus in FSHD. Using induced pluripotent stem cells (hIPSC), we further examined whether chromatin organization is inherited after reprogramming or acquired during differentiation and showed that folding of the 4q35 region is modified upon differentiation. These results together with previous findings highlight the role of the D4Z4 macrosatellite repeat in the topological organization of chromatin and further indicate that the D4Z4-dependent 3D structure induces transcriptional changes of 4q35 genes expression.
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Affiliation(s)
| | | | - Julia Morere
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France
| | | | - Camille Dion
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France
| | - Cherif Badja
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France
| | - Stéphane Roche
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France
| | - Karine Nguyen
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France.,APHM, Laboratoire de Génétique Médicale, Hôpital de la Timone, Marseille, France
| | | | - Jérôme D Robin
- Aix Marseille Univ, INSERM, MMG, U 1251, Marseille, France.
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8
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Rubio K, Dobersch S, Barreto G. Functional interactions between scaffold proteins, noncoding RNAs, and genome loci induce liquid-liquid phase separation as organizing principle for 3-dimensional nuclear architecture: implications in cancer. FASEB J 2019; 33:5814-5822. [PMID: 30742773 DOI: 10.1096/fj.201802715r] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eukaryotic cell nucleus consists of functionally specialized subcompartments. These nuclear subcompartments are biomolecular aggregates built of proteins, transcripts, and specific genome loci. The structure and function of each nuclear subcompartment are defined by the composition and dynamic interaction between these 3 components. The spatio-temporal localization of biochemical reactions into membraneless nuclear subcompartments can be achieved through liquid-liquid phase separation. Based on this organizing principle, nuclear subcompartments are droplet-like structures that adopt spherical shapes, flow, and fuse like liquids or gels. In the present review, we bring into the spotlight seminal works elucidating the functional interactions between scaffold proteins, noncoding RNAs, and genomic loci, thereby inducing liquid-liquid phase separation as an organizing principle for 3-dimensional nuclear architecture. We also discuss the implications in different cancer types as well as the potential use of this knowledge to develop novel therapeutic strategies against cancer.-Rubio, K., Dobersch, S., Barreto, G. Functional interactions between scaffold proteins, noncoding RNAs, and genome loci induce liquid-liquid phase separation as organizing principle for 3-dimensional nuclear architecture: implications in cancer.
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Affiliation(s)
- Karla Rubio
- Lung Cancer Epigenetic, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany
| | - Stephanie Dobersch
- Lung Cancer Epigenetic, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany
| | - Guillermo Barreto
- Lung Cancer Epigenetic, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany.,Laboratoire Croissance, Réparation, et Régénération Tissulaires (CRRET), Centre National de la Recherche Scientifique (CNRS) Équipe de Recherche Labellisée (ERL) 9215, Université Paris Est Créteil, Créteil, France.,Institute of Fundamental Medicine and Biology, Kazan (Volga Region) Federal University, Kazan, Russian Federation.,Excellence Cluster Cardio Pulmonary System (ECCPS), Universities of Giessen-Marburg Lung Center (UGMLC), Giessen, Germany.,German Center of Lung Research, Giessen, Germany
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9
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Laberthonnière C, Magdinier F, Robin JD. Bring It to an End: Does Telomeres Size Matter? Cells 2019; 8:E30. [PMID: 30626097 PMCID: PMC6356554 DOI: 10.3390/cells8010030] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 01/01/2019] [Accepted: 01/04/2019] [Indexed: 12/22/2022] Open
Abstract
Telomeres are unique nucleoprotein structures. Found at the edge of each chromosome, their main purpose is to mask DNA ends from the DNA-repair machinery by formation of protective loops. Through life and cell divisions, telomeres shorten and bring cells closer to either cell proliferation crisis or senescence. Beyond this mitotic clock role attributed to the need for telomere to be maintained over a critical length, the very tip of our DNA has been shown to impact transcription by position effect. TPE and a long-reach counterpart, TPE-OLD, are mechanisms recently described in human biology. Still in infancy, the mechanism of action of these processes and their respective genome wide impact remain to be resolved. In this review, we will discuss recent findings on telomere dynamics, TPE, TPE-OLD, and lessons learnt from model organisms.
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Affiliation(s)
| | - Frédérique Magdinier
- Aix Marseille Univ, MMG, Marseille Medical Genetics U1251, 13385 Marseille, France.
| | - Jérôme D Robin
- Aix Marseille Univ, MMG, Marseille Medical Genetics U1251, 13385 Marseille, France.
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10
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Smith ED, Garza-Gongora AG, MacQuarrie KL, Kosak ST. Interstitial telomeric loops and implications of the interaction between TRF2 and lamin A/C. Differentiation 2018; 102:19-26. [PMID: 29979997 DOI: 10.1016/j.diff.2018.06.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 06/11/2018] [Accepted: 06/12/2018] [Indexed: 11/19/2022]
Abstract
The protein-DNA complexes that compose the end of mammalian chromosomes-telomeres-serve to stabilize linear genomic DNA and are involved in cellular and organismal aging. One mechanism that protects telomeres from premature degradation is the formation of structures called t-loops, in which the single-stranded 3' overhang present at the terminal end of telomeres loops back and invades medial double-stranded telomeric DNA. We identified looped structures formed between terminal chromosome ends and interstitial telomeric sequences (ITSs), which are found throughout the human genome, that we have termed interstitial telomeric loops (ITLs). While they form in a TRF2-dependent manner similar to t-loops, ITLs further require the physical interaction of TRF2 with the nuclear intermediate filament protein lamin A/C. Our findings suggest that interactions between telomeres and the nucleoskeleton broadly impact genomic integrity, including telomere stability, chromosome structure, and chromosome fragility. Here, we review the roles of TRF2 and lamin A/C in telomere biology and consider how their interaction may relate telomere homeostasis to cellular and organismal aging.
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Affiliation(s)
- Erica D Smith
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Arturo G Garza-Gongora
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Kyle L MacQuarrie
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; Division of Hematology, Oncology and Stem Cell Transplantation, Ann & Robert H. Lurie Children's Hospital of Chicago, USA
| | - Steven T Kosak
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
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Bikkul MU, Clements CS, Godwin LS, Goldberg MW, Kill IR, Bridger JM. Farnesyltransferase inhibitor and rapamycin correct aberrant genome organisation and decrease DNA damage respectively, in Hutchinson-Gilford progeria syndrome fibroblasts. Biogerontology 2018; 19:579-602. [PMID: 29907918 PMCID: PMC6223735 DOI: 10.1007/s10522-018-9758-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Accepted: 05/30/2018] [Indexed: 12/20/2022]
Abstract
Hutchinson–Gilford progeria syndrome (HGPS) is a rare and fatal premature ageing disease in children. HGPS is one of several progeroid syndromes caused by mutations in the LMNA gene encoding the nuclear structural proteins lamins A and C. In classic HGPS the mutation G608G leads to the formation of a toxic lamin A protein called progerin. During post-translational processing progerin remains farnesylated owing to the mutation interfering with a step whereby the farnesyl moiety is removed by the enzyme ZMPSTE24. Permanent farnesylation of progerin is thought to be responsible for the proteins toxicity. Farnesyl is generated through the mevalonate pathway and three drugs that interfere with this pathway and hence the farnesylation of proteins have been administered to HGPS children in clinical trials. These are a farnesyltransferase inhibitor (FTI), statin and a bisphosphonate. Further experimental studies have revealed that other drugs such as N-acetyl cysteine, rapamycin and IGF-1 may be of use in treating HGPS through other pathways. We have shown previously that FTIs restore chromosome positioning in interphase HGPS nuclei. Mis-localisation of chromosomes could affect the cells ability to regulate proper genome function. Using nine different drug treatments representing drug regimes in the clinic we have shown that combinatorial treatments containing FTIs are most effective in restoring specific chromosome positioning towards the nuclear periphery and in tethering telomeres to the nucleoskeleton. On the other hand, rapamycin was found to be detrimental to telomere tethering, it was, nonetheless, the most effective at inducing DNA damage repair, as revealed by COMET analyses.
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Affiliation(s)
- Mehmet U Bikkul
- Progeria Research Team, Healthy Ageing Theme, Institute for Environment, Health and Societies, College of Health and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, UK
| | - Craig S Clements
- Progeria Research Team, Healthy Ageing Theme, Institute for Environment, Health and Societies, College of Health and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, UK
| | - Lauren S Godwin
- Progeria Research Team, Healthy Ageing Theme, Institute for Environment, Health and Societies, College of Health and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, UK
| | - Martin W Goldberg
- Department of Biosciences, Durham University, Science Laboratories, South Road, Durham, DH1 3LE, UK
| | - Ian R Kill
- Progeria Research Team, Healthy Ageing Theme, Institute for Environment, Health and Societies, College of Health and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, UK
| | - Joanna M Bridger
- Progeria Research Team, Healthy Ageing Theme, Institute for Environment, Health and Societies, College of Health and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, UK.
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Szczesny SE, Mauck RL. The Nuclear Option: Evidence Implicating the Cell Nucleus in Mechanotransduction. J Biomech Eng 2017; 139:2592356. [PMID: 27918797 DOI: 10.1115/1.4035350] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Indexed: 02/06/2023]
Abstract
Biophysical stimuli presented to cells via microenvironmental properties (e.g., alignment and stiffness) or external forces have a significant impact on cell function and behavior. Recently, the cell nucleus has been identified as a mechanosensitive organelle that contributes to the perception and response to mechanical stimuli. However, the specific mechanotransduction mechanisms that mediate these effects have not been clearly established. Here, we offer a comprehensive review of the evidence supporting (and refuting) three hypothetical nuclear mechanotransduction mechanisms: physical reorganization of chromatin, signaling at the nuclear envelope, and altered cytoskeletal structure/tension due to nuclear remodeling. Our goal is to provide a reference detailing the progress that has been made and the areas that still require investigation regarding the role of nuclear mechanotransduction in cell biology. Additionally, we will briefly discuss the role that mathematical models of cell mechanics can play in testing these hypotheses and in elucidating how biophysical stimulation of the nucleus drives changes in cell behavior. While force-induced alterations in signaling pathways involving lamina-associated polypeptides (LAPs) (e.g., emerin and histone deacetylase 3 (HDAC3)) and transcription factors (TFs) located at the nuclear envelope currently appear to be the most clearly supported mechanism of nuclear mechanotransduction, additional work is required to examine this process in detail and to more fully test alternative mechanisms. The combination of sophisticated experimental techniques and advanced mathematical models is necessary to enhance our understanding of the role of the nucleus in the mechanotransduction processes driving numerous critical cell functions.
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Affiliation(s)
- Spencer E Szczesny
- Department of Orthopaedic Surgery, University of Pennsylvania, 424 Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104; Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, PA 19104
| | - Robert L Mauck
- Department of Orthopaedic Surgery, University of Pennsylvania, 424 Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104; Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, PA 19104;Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104 e-mail:
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13
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Serebryannyy L, Misteli T. Protein sequestration at the nuclear periphery as a potential regulatory mechanism in premature aging. J Cell Biol 2017; 217:21-37. [PMID: 29051264 PMCID: PMC5748986 DOI: 10.1083/jcb.201706061] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Revised: 08/10/2017] [Accepted: 08/17/2017] [Indexed: 12/19/2022] Open
Abstract
Serebryannyy and Misteli provide a perspective on how protein sequestration at the inner nuclear membrane and nuclear lamina might influence aging. Despite the extensive description of numerous molecular changes associated with aging, insights into the driver mechanisms of this fundamental biological process are limited. Based on observations in the premature aging syndrome Hutchinson–Gilford progeria, we explore the possibility that protein regulation at the inner nuclear membrane and the nuclear lamina contributes to the aging process. In support, sequestration of nucleoplasmic proteins to the periphery impacts cell stemness, the response to cytotoxicity, proliferation, changes in chromatin state, and telomere stability. These observations point to the nuclear periphery as a central regulator of the aging phenotype.
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Affiliation(s)
| | - Tom Misteli
- National Cancer Institute, National Institutes of Health, Bethesda, MD
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14
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Abstract
Chromosome ends are complex structures, which require a panel of factors for their elongation, replication, and protection. We describe here the mechanics of mammalian telomeres, dynamics and maintainance in relation to lamins. Multiple biochemical connections, including association of telomeres to the nuclear envelope and matrix, of telomeric proteins to lamins, and of lamin-associated proteins to chromosome ends, underline the interplay between lamins and telomeres. Paths toward senescence, such as defective telomere replication, altered heterochromatin organization, and impaired DNA repair, are common to lamins' and telomeres' dysfunction. The convergence of phenotypes can be interpreted through a model of dynamic, lamin-controlled functional platforms dedicated to the function of telomeres as fragile sites. The features of telomeropathies and laminopathies, and of animal models underline further overlapping aspects, including the alteration of stem cell compartments. We expect that future studies of basic biology and on aging will benefit from the analysis of this telomere-lamina interplay.
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Affiliation(s)
- Romina Burla
- a Dipartimento di Biologia e Biotecnologie "C. Darwin," Sapienza Università di Roma , Rome, Italy.,b Istituto di Biologia e Patologia Molecolari del CNR , Rome , Italy
| | - Mattia La Torre
- a Dipartimento di Biologia e Biotecnologie "C. Darwin," Sapienza Università di Roma , Rome, Italy
| | - Isabella Saggio
- a Dipartimento di Biologia e Biotecnologie "C. Darwin," Sapienza Università di Roma , Rome, Italy.,b Istituto di Biologia e Patologia Molecolari del CNR , Rome , Italy.,c Istituto Pasteur Fondazione Cenci Bolognetti , Rome , Italy
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15
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Casa V, Runfola V, Micheloni S, Aziz A, Dilworth FJ, Gabellini D. Polycomb repressive complex 1 provides a molecular explanation for repeat copy number dependency in FSHD muscular dystrophy. Hum Mol Genet 2017; 26:753-767. [PMID: 28040729 PMCID: PMC5409123 DOI: 10.1093/hmg/ddw426] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 12/15/2016] [Indexed: 11/13/2022] Open
Abstract
Repression of repetitive elements is crucial to preserve genome integrity and has been traditionally ascribed to constitutive heterochromatin pathways. FacioScapuloHumeral Muscular Dystrophy (FSHD), one of the most common myopathies, is characterized by a complex interplay of genetic and epigenetic events. The main FSHD form is linked to a reduced copy number of the D4Z4 macrosatellite repeat on 4q35, causing loss of silencing and aberrant expression of the D4Z4-embedded DUX4 gene leading to disease. By an unknown mechanism, D4Z4 copy-number correlates with FSHD phenotype. Here we show that the DUX4 proximal promoter (DUX4p) is sufficient to nucleate the enrichment of both constitutive and facultative heterochromatin components and to mediate a copy-number dependent gene silencing. We found that both the CpG/GC dense DNA content and the repetitive nature of DUX4p arrays are important for their repressive ability. We showed that DUX4p mediates a copy number-dependent Polycomb Repressive Complex 1 (PRC1) recruitment, which is responsible for the copy-number dependent gene repression. Overall, we directly link genetic and epigenetic defects in FSHD by proposing a novel molecular explanation for the copy number-dependency in FSHD pathogenesis, and offer insight into the molecular functions of repeats in chromatin regulation.
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Affiliation(s)
- Valentina Casa
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy.,Università Vita-Salute San Raffaele, Milan 20132, Italy
| | - Valeria Runfola
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
| | - Stefano Micheloni
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
| | - Arif Aziz
- The Sprott Center for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada
| | - F Jeffrey Dilworth
- The Sprott Center for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada
| | - Davide Gabellini
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy.,Dulbecco Telethon Institute, Milan 20132, Italy
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16
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Robin JD, Magdinier F. Physiological and Pathological Aging Affects Chromatin Dynamics, Structure and Function at the Nuclear Edge. Front Genet 2016; 7:153. [PMID: 27602048 PMCID: PMC4993774 DOI: 10.3389/fgene.2016.00153] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Accepted: 08/08/2016] [Indexed: 01/29/2023] Open
Abstract
Lamins are intermediate filaments that form a complex meshwork at the inner nuclear membrane. Mammalian cells express two types of Lamins, Lamins A/C and Lamins B, encoded by three different genes, LMNA, LMNB1, and LMNB2. Mutations in the LMNA gene are associated with a group of phenotypically diverse diseases referred to as laminopathies. Lamins interact with a large number of binding partners including proteins of the nuclear envelope but also chromatin-associated factors. Lamins not only constitute a scaffold for nuclear shape, rigidity and resistance to stress but also contribute to the organization of chromatin and chromosomal domains. We will discuss here the impact of A-type Lamins loss on alterations of chromatin organization and formation of chromatin domains and how disorganization of the lamina contributes to the patho-physiology of premature aging syndromes.
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Affiliation(s)
- Jérôme D Robin
- IRCAN, CNRS UMR 7284/INSERM U1081, Faculté de Médecine Nice, France
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17
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Nuclear envelope proteins modulate proliferation of vascular smooth muscle cells during cyclic stretch application. Proc Natl Acad Sci U S A 2016; 113:5293-8. [PMID: 27114541 DOI: 10.1073/pnas.1604569113] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Cyclic stretch is an important inducer of vascular smooth muscle cell (VSMC) proliferation, which is crucial in vascular remodeling during hypertension. However, the molecular mechanism remains unclear. We studied the effects of emerin and lamin A/C, two important nuclear envelope proteins, on VSMC proliferation in hypertension and the underlying mechano-mechanisms. In common carotid artery of hypertensive rats in vivo and in cultured cells subjected to high (15%) cyclic stretch in vitro, VSMC proliferation was increased significantly, and the expression of emerin and lamin A/C was repressed compared with normotensive or normal (5%) cyclic stretch controls. Using targeted siRNA to mimic the repressed expression of emerin or lamin A/C induced by 15% stretch, we found that VSMC proliferation was enhanced under static and 5%-stretch conditions. Overexpression of emerin or lamin A/C reversed VSMC proliferation induced by 15% stretch. Hence, emerin and lamin A/C play critical roles in suppressing VSMC hyperproliferation induced by hyperstretch. ChIP-on-chip and MOTIF analyses showed that the DNAs binding with emerin contain three transcription factor motifs: CCNGGA, CCMGCC, and ABTTCCG; DNAs binding with lamin A/C contain the motifs CVGGAA, GCCGCYGC, and DAAGAAA. Protein/DNA array proved that altered emerin or lamin A/C expression modulated the activation of various transcription factors. Furthermore, accelerating local expression of emerin or lamin A/C reversed cell proliferation in the carotid artery of hypertensive rats in vivo. Our findings establish the pathogenetic role of emerin and lamin A/C repression in stretch-induced VSMC proliferation and suggest mechanobiological mechanism underlying this process that involves the sequence-specific binding of emerin and lamin A/C to specific transcription factor motifs.
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18
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Finding a place in the SUN: telomere maintenance in a diverse nuclear landscape. Curr Opin Cell Biol 2016; 40:145-152. [PMID: 27064212 DOI: 10.1016/j.ceb.2016.03.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 03/15/2016] [Accepted: 03/18/2016] [Indexed: 11/21/2022]
Abstract
Telomeres function in the context of a complex nuclear milieu in which telomeres tend to occupy distinct subnuclear regions. Indeed, regulation of the subnuclear positioning of telomeres is conserved from yeast to human, raising the age-old question: to what extent is location important for function? In mitotically dividing cells, the positioning of telomeres affects their epigenetic state and influences telomere processing and synthesis. In meiotic cells, telomere location is important for homologue pairing, centromere assembly and spindle formation. Here we focus on recent insights into the functions of telomere positioning in maintaining genome integrity.
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19
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Gonzalo S, Eissenberg JC. Tying up loose ends: telomeres, genomic instability and lamins. Curr Opin Genet Dev 2016; 37:109-118. [PMID: 27010504 DOI: 10.1016/j.gde.2016.03.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Revised: 02/29/2016] [Accepted: 03/05/2016] [Indexed: 01/04/2023]
Abstract
On casual inspection, the eukaryotic nucleus is a deceptively simple organelle. Far from being a bag of chromatin, the nucleus is, in some ways, a structural and functional extension of the chromosomes it contains. Recently, interest has intensified in how chromosome compartmentalization and dynamics affect nuclear function. Different studies uncovered functional interactions between chromosomes and the filamentous nuclear meshwork comprised of lamin proteins. Here, we summarize recent research suggesting that telomeres, the capping structures that protect chromosome ends, are stabilized by lamin-binding and that alterations in nuclear lamins lead to defects in telomere compartmentalization, homeostasis and function. Telomere dysfunction contributes to the genomic instability that characterizes aging-related diseases, and might be an important factor in the pathophysiology of lamin-related diseases.
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Affiliation(s)
- Susana Gonzalo
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Doisy Research Center, 1100 South Grand Blvd., St. Louis, MO 63104, USA.
| | - Joel C Eissenberg
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Doisy Research Center, 1100 South Grand Blvd., St. Louis, MO 63104, USA
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20
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Meinke P, Schirmer EC. LINC'ing form and function at the nuclear envelope. FEBS Lett 2015; 589:2514-21. [PMID: 26096784 DOI: 10.1016/j.febslet.2015.06.011] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2015] [Revised: 06/03/2015] [Accepted: 06/06/2015] [Indexed: 11/15/2022]
Abstract
The nuclear envelope is an amazing piece of engineering. On one hand it is built like a mediaeval fortress with filament systems reinforcing its membrane walls and its double membrane structure forming a lumen like a castle moat. On the other hand its structure can adapt while maintaining its integrity like a reed bending in a river. Like a fortress it has guarded drawbridges in the nuclear pore complexes, but also has other mechanical means of communication. All this is enabled largely because of the LINC complex, a multi-protein structure that connects the intermediate filament nucleoskeleton across the lumen of the double membrane nuclear envelope to multiple cytoplasmic filament systems that themselves could act simultaneously both like mediaeval buttresses and like lines on a suspension bridge. Although many details of the greater LINC structure remain to be discerned, a number of recent findings are giving clues as to how its structural organization can yield such striking dynamic yet stable properties. Combining double- and triple-helical coiled-coils, intrinsic disorder and order, tissue-specific components, and intermediate filaments enables these unique properties.
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Affiliation(s)
- Peter Meinke
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, UK.
| | - Eric C Schirmer
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, UK
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21
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Steglich B, Strålfors A, Khorosjutina O, Persson J, Smialowska A, Javerzat JP, Ekwall K. The Fun30 chromatin remodeler Fft3 controls nuclear organization and chromatin structure of insulators and subtelomeres in fission yeast. PLoS Genet 2015; 11:e1005101. [PMID: 25798942 PMCID: PMC4370569 DOI: 10.1371/journal.pgen.1005101] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Accepted: 02/25/2015] [Indexed: 12/21/2022] Open
Abstract
In eukaryotic cells, local chromatin structure and chromatin organization in the nucleus both influence transcriptional regulation. At the local level, the Fun30 chromatin remodeler Fft3 is essential for maintaining proper chromatin structure at centromeres and subtelomeres in fission yeast. Using genome-wide mapping and live cell imaging, we show that this role is linked to controlling nuclear organization of its targets. In fft3∆ cells, subtelomeres lose their association with the LEM domain protein Man1 at the nuclear periphery and move to the interior of the nucleus. Furthermore, genes in these domains are upregulated and active chromatin marks increase. Fft3 is also enriched at retrotransposon-derived long terminal repeat (LTR) elements and at tRNA genes. In cells lacking Fft3, these sites lose their peripheral positioning and show reduced nucleosome occupancy. We propose that Fft3 has a global role in mediating association between specific chromatin domains and the nuclear envelope. In the genome of eukaryotic cells, domains of active and repressive chromatin alternate along the chromosome arms. Insulator elements are necessary to shield these different environments from each other. In the fission yeast Schizosaccharomyces pombe, the chromatin remodeler Fft3 is required to maintain the repressed subtelomeric chromatin. Here we show that Fft3 maintains nucleosome structure of insulator elements at the subtelomeric borders. We also observe that subtelomeres and insulator elements move away from the nuclear envelope in cells lacking Fft3. The nuclear periphery is known to harbor repressive chromatin in many eukaryotes and has been implied in insulator function. Our results suggest that chromatin remodeling through Fft3 is required to maintain proper chromatin structure and nuclear organization of insulator elements.
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Affiliation(s)
- Babett Steglich
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
| | - Annelie Strålfors
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
| | - Olga Khorosjutina
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
| | - Jenna Persson
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
| | - Agata Smialowska
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
| | - Jean-Paul Javerzat
- Univ. Bordeaux, Institut de Biochimie et Génétique Cellulaires, UMR 5095, Bordeaux, France
- CNRS, Institut de Biochimie et Génétique Cellulaires, UMR 5095, Bordeaux, France
| | - Karl Ekwall
- Department of Biosciences and Nutrition; Center for Innovative Medicine, Karolinska Institutet, Novum Building, Huddinge, Sweden
- * E-mail:
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22
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The lncRNA Firre anchors the inactive X chromosome to the nucleolus by binding CTCF and maintains H3K27me3 methylation. Genome Biol 2015; 16:52. [PMID: 25887447 PMCID: PMC4391730 DOI: 10.1186/s13059-015-0618-0] [Citation(s) in RCA: 187] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Accepted: 02/23/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In mammals, X chromosome genes are present in one copy in males and two in females. To balance the dosage of X-linked gene expression between the sexes, one of the X chromosomes in females is silenced. X inactivation is initiated by upregulation of the lncRNA (long non-coding RNA) Xist and recruitment of specific chromatin modifiers. The inactivated X chromosome becomes heterochromatic and visits a specific nuclear compartment adjacent to the nucleolus. RESULTS Here, we show a novel role for the lncRNA Firre in anchoring the inactive mouse X chromosome and preserving one of its main epigenetic features, H3K27me3. Similar to Dxz4, Firre is X-linked and expressed from a macrosatellite repeat locus associated with a cluster of CTCF and cohesin binding sites, and is preferentially located adjacent to the nucleolus. CTCF binding present initially in both male and female mouse embryonic stem cells is lost from the active X during development. Knockdown of Firre disrupts perinucleolar targeting and H3K27me3 levels in mouse fibroblasts, demonstrating a role in maintenance of an important epigenetic feature of the inactive X chromosome. No X-linked gene reactivation is seen after Firre knockdown; however, a compensatory increase in the expression of chromatin modifier genes implicated in X silencing is observed. Further experiments in female embryonic stem cells suggest that Firre does not play a role in X inactivation onset. CONCLUSIONS The X-linked lncRNA Firre helps to position the inactive X chromosome near the nucleolus and to preserve one of its main epigenetic features.
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23
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Gruenbaum Y, Foisner R. Lamins: nuclear intermediate filament proteins with fundamental functions in nuclear mechanics and genome regulation. Annu Rev Biochem 2015; 84:131-64. [PMID: 25747401 DOI: 10.1146/annurev-biochem-060614-034115] [Citation(s) in RCA: 368] [Impact Index Per Article: 40.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Lamins are intermediate filament proteins that form a scaffold, termed nuclear lamina, at the nuclear periphery. A small fraction of lamins also localize throughout the nucleoplasm. Lamins bind to a growing number of nuclear protein complexes and are implicated in both nuclear and cytoskeletal organization, mechanical stability, chromatin organization, gene regulation, genome stability, differentiation, and tissue-specific functions. The lamin-based complexes and their specific functions also provide insights into possible disease mechanisms for human laminopathies, ranging from muscular dystrophy to accelerated aging, as observed in Hutchinson-Gilford progeria and atypical Werner syndromes.
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Affiliation(s)
- Yosef Gruenbaum
- Department of Genetics, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel;
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24
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DNA methylation analysis of the macrosatellite repeat associated with FSHD muscular dystrophy at single nucleotide level. PLoS One 2014; 9:e115278. [PMID: 25545674 PMCID: PMC4278900 DOI: 10.1371/journal.pone.0115278] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 11/23/2014] [Indexed: 11/26/2022] Open
Abstract
Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common inherited diseases of the skeletal muscle. It is characterized by asymmetric muscle weakness and variable penetrance. FSHD is linked to a reduction in copy number of the D4Z4 3.3 kb macrosatellite repeat, located in 4q35. This causes the epigenetic de-repression of FSHD candidate genes leading to disease. Nevertheless, the molecular mechanism responsible for silencing of FSHD candidate genes in healthy subjects is not fully understood. While a role for DNA methylation has been suggested, so far there is limited information regarding the methylation status of the 325 CpGs contained in each D4Z4 unit. Using a human/rodent monochromosomal hybrid cell line containing a single human chromosome 4, we performed an in depth analysis of DNA methylation for the majority of the CpGs inside D4Z4 at single nucleotide level. We found that D4Z4 is not uniformly methylated and that the level of DNA methylation does not correlate with the density of CpG dinucleotides. Moreover, in several D4Z4 regions characterized by near complete methylation, we found specific unmethylated CpGs. These elements are enriched in transcription factor binding sites that could be involved in muscle-specific D4Z4 activity. Our approach also detected differential methylation among different D4Z4 units, suggesting that the D4Z4 array is a mosaic of euchromatic and heterochromatic domains. Finally, we found that DNA methylation and histone de-acetylation are required to maintain FSHD candidate genes repressed. Taken together, our data underscore new players involved in the epigenetic regulation of the FSHD locus that could be targeted for therapeutic purposes.
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25
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26
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Colangelo V, François S, Soldà G, Picco R, Roma F, Ginelli E, Meneveri R. Next-generation sequencing analysis of miRNA expression in control and FSHD myogenesis. PLoS One 2014; 9:e108411. [PMID: 25285664 PMCID: PMC4186784 DOI: 10.1371/journal.pone.0108411] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 08/28/2014] [Indexed: 02/07/2023] Open
Abstract
Emerging evidence has demonstrated that miRNA sequences can regulate skeletal myogenesis by controlling the process of myoblast proliferation and differentiation. However, at present a deep analysis of miRNA expression in control and FSHD myoblasts during differentiation has not yet been derived. To close this gap, we used a next-generation sequencing (NGS) approach applied to in vitro myogenesis. Furthermore, to minimize sample genetic heterogeneity and muscle-type specific patterns of gene expression, miRNA profiling from NGS data was filtered with FC≥4 (log2FC≥2) and p-value<0.05, and its validation was derived by qRT-PCR on myoblasts from seven muscle districts. In particular, control myogenesis showed the modulation of 38 miRNAs, the majority of which (34 out 38) were up-regulated, including myomiRs (miR-1, -133a, -133b and -206). Approximately one third of the modulated miRNAs were not previously reported to be involved in muscle differentiation, and interestingly some of these (i.e. miR-874, -1290, -95 and -146a) were previously shown to regulate cell proliferation and differentiation. FSHD myogenesis evidenced a reduced number of modulated miRNAs than healthy muscle cells. The two processes shared nine miRNAs, including myomiRs, although with FC values lower in FSHD than in control cells. In addition, FSHD cells showed the modulation of six miRNAs (miR-1268, -1268b, -1908, 4258, -4508- and -4516) not evidenced in control cells and that therefore could be considered FSHD-specific, likewise three novel miRNAs that seem to be specifically expressed in FSHD myotubes. These data further clarify the impact of miRNA regulation during control myogenesis and strongly suggest that a complex dysregulation of miRNA expression characterizes FSHD, impairing two important features of myogenesis: cell cycle and muscle development. The derived miRNA profiling could represent a novel molecular signature for FSHD that includes diagnostic biomarkers and possibly therapeutic targets.
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Affiliation(s)
- Veronica Colangelo
- Department of Health Sciences, University of Milano-Bicocca, Monza, Italy
| | - Stéphanie François
- Department of Health Sciences, University of Milano-Bicocca, Monza, Italy
| | - Giulia Soldà
- Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy
| | - Raffaella Picco
- Department of Medical and Biological Sciences, University of Udine, Udine, Italy
| | - Francesca Roma
- Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy
| | - Enrico Ginelli
- Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy
| | - Raffaella Meneveri
- Department of Health Sciences, University of Milano-Bicocca, Monza, Italy
- * E-mail:
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27
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Abstract
Telomeres protect chromosome ends from degradation and inappropriate DNA damage response activation through their association with specific factors. Interestingly, these telomeric factors are able to localize outside telomeric regions, where they can regulate the transcription of genes involved in metabolism, immunity and differentiation. These findings delineate a signalling pathway by which telomeric changes control the ability of their associated factors to regulate transcription. This mechanism is expected to enable a greater diversity of cellular responses that are adapted to specific cell types and telomeric changes, and may therefore represent a pivotal aspect of development, ageing and telomere-mediated diseases.
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28
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Stong N, Deng Z, Gupta R, Hu S, Paul S, Weiner AK, Eichler EE, Graves T, Fronick CC, Courtney L, Wilson RK, Lieberman PM, Davuluri RV, Riethman H. Subtelomeric CTCF and cohesin binding site organization using improved subtelomere assemblies and a novel annotation pipeline. Genome Res 2014; 24:1039-50. [PMID: 24676094 PMCID: PMC4032850 DOI: 10.1101/gr.166983.113] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 03/26/2014] [Indexed: 12/25/2022]
Abstract
Mapping genome-wide data to human subtelomeres has been problematic due to the incomplete assembly and challenges of low-copy repetitive DNA elements. Here, we provide updated human subtelomere sequence assemblies that were extended by filling telomere-adjacent gaps using clone-based resources. A bioinformatic pipeline incorporating multiread mapping for annotation of the updated assemblies using short-read data sets was developed and implemented. Annotation of subtelomeric sequence features as well as mapping of CTCF and cohesin binding sites using ChIP-seq data sets from multiple human cell types confirmed that CTCF and cohesin bind within 3 kb of the start of terminal repeat tracts at many, but not all, subtelomeres. CTCF and cohesin co-occupancy were also enriched near internal telomere-like sequence (ITS) islands and the nonterminal boundaries of subtelomere repeat elements (SREs) in transformed lymphoblastoid cell lines (LCLs) and human embryonic stem cell (ES) lines, but were not significantly enriched in the primary fibroblast IMR90 cell line. Subtelomeric CTCF and cohesin sites predicted by ChIP-seq using our bioinformatics pipeline (but not predicted when only uniquely mapping reads were considered) were consistently validated by ChIP-qPCR. The colocalized CTCF and cohesin sites in SRE regions are candidates for mediating long-range chromatin interactions in the transcript-rich SRE region. A public browser for the integrated display of short-read sequence-based annotations relative to key subtelomere features such as the start of each terminal repeat tract, SRE identity and organization, and subtelomeric gene models was established.
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Affiliation(s)
- Nicholas Stong
- Graduate Group in Genomics and Computational Biology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
| | - Zhong Deng
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
| | - Ravi Gupta
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
| | - Sufen Hu
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
| | - Shiela Paul
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
| | | | - Evan E. Eichler
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195, USA
| | - Tina Graves
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri 63108, USA
| | - Catrina C. Fronick
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri 63108, USA
| | - Laura Courtney
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri 63108, USA
| | - Richard K. Wilson
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri 63108, USA
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Amendola M, van Steensel B. Mechanisms and dynamics of nuclear lamina–genome interactions. Curr Opin Cell Biol 2014; 28:61-8. [DOI: 10.1016/j.ceb.2014.03.003] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Revised: 03/06/2014] [Accepted: 03/08/2014] [Indexed: 12/21/2022]
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Arancio W, Pizzolanti G, Genovese SI, Pitrone M, Giordano C. Epigenetic involvement in Hutchinson-Gilford progeria syndrome: a mini-review. Gerontology 2014; 60:197-203. [PMID: 24603298 DOI: 10.1159/000357206] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 11/11/2013] [Indexed: 11/19/2022] Open
Abstract
Hutchinson-Gilford progeria syndrome (HGPS) is a rare human genetic disease that leads to a severe premature ageing phenotype, caused by mutations in the LMNA gene. The LMNA gene codes for lamin-A and lamin-C proteins, which are structural components of the nuclear lamina. HGPS is usually caused by a de novo C1824T mutation that leads to the accumulation of a dominant negative form of lamin-A called progerin. Progerin also accumulates physiologically in normal ageing cells as a rare splicing form of lamin-A transcripts. From this perspective, HGPS cells seem to be good candidates for the study of the physiological mechanisms of ageing. Progerin accumulation leads to faster cellular senescence, stem cell depletion and the progeroid phenotype. Tissues of mesodermic origin are especially affected by HGPS. HGPS patients usually have a bad quality of life and, with current treatments, their life expectancy does not exceed their second decade at best. Though progerin can be expressed in almost any tissue, when death occurs, it is usually due to cardiovascular complications. In HGPS, severe epigenetic alterations have been reported. Histone-covalent modifications are radically different from control specimens, with the tendency to lose the bipartition into euchromatin and heterochromatin. This is reflected in an altered spatial compartmentalization and conformation of chromatin within the nucleus. Moreover, it seems that microRNAs and microRNA biosynthesis might play a role in HGPS. Exemplary in this connection is the suggested protective effect of miR-9 on the central nervous system of affected individuals. This mini-review will report on the state of the art of HGPS epigenetics, and there will be a discussion of how epigenetic alterations in HGPS cells can alter the cellular metabolism and lead to the systemic syndrome.
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Affiliation(s)
- Walter Arancio
- Section of Endocrinology, Diabetology and Metabolism, Biomedical Department of Internal and Specialized Medicine (DiBiMIS), University of Palermo, Palermo, Italy
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Abstract
Heterochromatin displays repressive histone marks that down-regulate transcription. In the absence of specialized barriers, these repressive marks spread onto nearby nucleosomes and induce transcriptional silencing of these regions. Accordingly, in various species, transgenes that are experimentally inserted directly next to telomeric repeats are silenced. Transcriptional repression induced by the spreading of telomeric heterochromatin is known as the "telomere position effect". Although it is attenuated by the presence of natural subtelomeric barriers acting against the spreading of telomeric heterochromatin, telomere-induced silencing is also observed at the level of endogenous loci where it was initially proposed to provide a mean to regulate gene expression during senescence. This, however, remains to be formally demonstrated. Here, I review the current evidences for a telomere position effect, from yeast to human.
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Affiliation(s)
- Anabelle Decottignies
- Altérations génétiques et épigénétiques des génomes, Institut de Duve, université catholique de Louvain, avenue Hippocrate 75, 1200 Bruxelles, Belgique
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Dalmasso MC, Carmona SJ, Angel SO, Agüero F. Characterization of Toxoplasma gondii subtelomeric-like regions: identification of a long-range compositional bias that is also associated with gene-poor regions. BMC Genomics 2014; 15:21. [PMID: 24417889 PMCID: PMC4008256 DOI: 10.1186/1471-2164-15-21] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 01/02/2014] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND Chromosome ends are composed of telomeric repeats and subtelomeric regions, which are patchworks of genes interspersed with repeated elements. Although chromosome ends display similar arrangements in different species, their sequences are highly divergent. In addition, these regions display a particular nucleosomal composition and bind specific factors, therefore producing a special kind of heterochromatin. Using data from currently available draft genomes we have characterized these putative Telomeric Associated Sequences in Toxoplasma gondii. RESULTS An all-vs-all pairwise comparison of T. gondii assembled chromosomes revealed the presence of conserved regions of ∼ 30 Kb located near the ends of 9 of the 14 chromosomes of the genome of the ME49 strain. Sequence similarity among these regions is ∼ 70%, and they are also highly conserved in the GT1 and VEG strains. However, they are unique to Toxoplasma with no detectable similarity in other Apicomplexan parasites. The internal structure of these sequences consists of 3 repetitive regions separated by high-complexity sequences without annotated genes, except for a gene from the Toxoplasma Specific Family. ChIP-qPCR experiments showed that nucleosomes associated to these sequences are enriched in histone H4 monomethylated at K20 (H4K20me1), and the histone variant H2A.X, suggesting that they are silenced sequences (heterochromatin). A detailed characterization of the base composition of these sequences, led us to identify a strong long-range compositional bias, which was similar to that observed in other genomic silenced fragments such as those containing centromeric sequences, and was negatively correlated to gene density. CONCLUSIONS We identified and characterized a region present in most Toxoplasma assembled chromosomes. Based on their location, sequence features, and nucleosomal markers we propose that these might be part of subtelomeric regions of T. gondii. The identified regions display a unique trinucleotide compositional bias, which is shared (despite the lack of any detectable sequence similarity) with other silenced sequences, such as those making up the chromosome centromeres. We also identified other genomic regions with this compositional bias (but no detectable sequence similarity) that might be functionally similar.
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Affiliation(s)
| | | | - Sergio O Angel
- Instituto de Investigaciones Biotecnológicas - Instituto Tecnológico de Chascomús, UNSAM - CONICET, Sede Chascomús, Av, Intendente Marino Km 8, 2 CC 164, B 7130 IWA, Chascomús, Argentina.
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Abstract
Despite decades of research, cancer metastasis remains an incompletely understood process that is as complex as it is devastating. In recent years, there has been an increasing push to investigate the biomechanical aspects of tumorigenesis, complementing the research on genetic and biochemical changes. In contrast to the high genetic variability encountered in cancer cells, almost all metastatic cells are subject to the same physical constraints as they leave the primary tumor, invade surrounding tissues, transit through the circulatory system, and finally infiltrate new tissues. Advances in live cell imaging and other biophysical techniques, including measurements of subcellular mechanics, have yielded stunning new insights into the physics of cancer cells. While much of this research has been focused on the mechanics of the cytoskeleton and the cellular microenvironment, it is now emerging that the mechanical properties of the cell nucleus and its connection to the cytoskeleton may play a major role in cancer metastasis, as deformation of the large and stiff nucleus presents a substantial obstacle during the passage through the dense interstitial space and narrow capillaries. Here, we present an overview of the molecular components that govern the mechanical properties of the nucleus, and we discuss how changes in nuclear structure and composition observed in many cancers can modulate nuclear mechanics and promote metastatic processes. Improved insights into this interplay between nuclear mechanics and metastatic progression may have powerful implications in cancer diagnostics and therapy and may reveal novel therapeutic targets for pharmacological inhibition of cancer cell invasion.
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Affiliation(s)
- Celine Denais
- Department of Biomedical Engineering, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, 14853, USA,
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Peripheral subnuclear positioning suppresses Tcrb recombination and segregates Tcrb alleles from RAG2. Proc Natl Acad Sci U S A 2013; 110:E4628-37. [PMID: 24218622 DOI: 10.1073/pnas.1310846110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Allelic exclusion requires that the two alleles at antigen-receptor loci attempt to recombine variable (V), diversity (D), and joining (J) gene segments [V(D)J recombination] asynchronously in nuclei of developing lymphocytes. It previously was shown that T-cell receptor β (Tcrb) alleles frequently and stochastically associate with the nuclear lamina and pericentromeric heterochromatin in CD4(-)CD8(-) thymocytes. Moreover, rearranged alleles were underrepresented at these locations. Here we used 3D immunofluorescence in situ hybridization to identify recently rearranged Tcrb alleles based on the accumulation of the DNA-repair protein 53BP1. We found that Tcrb alleles recombine asynchronously in double-negative thymocytes and that V(D)J recombination is suppressed on peripheral as compared with central Tcrb alleles. Moreover, the recombination events that did take place at the nuclear periphery preferentially occurred on Tcrb alleles that were partially dissociated from the nuclear lamina. To understand better the mechanism by which V(D)J recombination is suppressed at the nuclear periphery, we evaluated the subnuclear distribution of recombination-activating gene 2 (RAG2) protein. We found that RAG2 abundance was reduced at the nuclear periphery. Moreover, RAG2 was distributed differently from RNA polymerase II and histone H3K4 trimethylation. Our data suggest that the nuclear periphery suppresses V(D)J recombination, at least in part, by segregating Tcrb alleles from RAG proteins.
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Acacetin and chrysin, two polyphenolic compounds, alleviate telomeric position effect in human cells. MOLECULAR THERAPY. NUCLEIC ACIDS 2013; 2:e116. [PMID: 23962900 PMCID: PMC3759739 DOI: 10.1038/mtna.2013.42] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Accepted: 06/04/2013] [Indexed: 12/28/2022]
Abstract
We took advantage of the ability of human telomeres to silence neighboring genes (telomere position effect or TPE) to design a high-throughput screening assay for drugs altering telomeres. We identified, for the first time, that two dietary flavones, acacetin and chrysin, are able to specifically alleviate TPE in human cells. We further investigated their influence on telomere integrity and showed that both drugs drastically deprotect telomeres against DNA damage response. However, telomere deprotection triggered by shelterin dysfunction does not affect TPE, indicating that acacetin and chrysin target several functions of telomeres. These results show that TPE-based screening assays represent valuable methods to discover new compounds targeting telomeres.
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Ritland Politz JC, Scalzo D, Groudine M. Something silent this way forms: the functional organization of the repressive nuclear compartment. Annu Rev Cell Dev Biol 2013; 29:241-70. [PMID: 23834025 PMCID: PMC3999972 DOI: 10.1146/annurev-cellbio-101512-122317] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The repressive compartment of the nucleus is comprised primarily of telomeric and centromeric regions, the silent portion of ribosomal RNA genes, the majority of transposable element repeats, and facultatively repressed genes specific to different cell types. This compartment localizes into three main regions: the peripheral heterochromatin, perinucleolar heterochromatin, and pericentromeric heterochromatin. Both chromatin remodeling proteins and transcription of noncoding RNAs are involved in maintenance of repression in these compartments. Global reorganization of the repressive compartment occurs at each cell division, during early development, and during terminal differentiation. Differential action of chromatin remodeling complexes and boundary element looping activities are involved in mediating these organizational changes. We discuss the evidence that heterochromatin formation and compartmentalization may drive nuclear organization.
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Affiliation(s)
| | - David Scalzo
- Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Mark Groudine
- Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
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Broucqsault N, Morere J, Gaillard MC, Dumonceaux J, Torrents J, Salort-Campana E, Maues De Paula A, Bartoli M, Fernandez C, Chesnais AL, Ferreboeuf M, Sarda L, Dufour H, Desnuelle C, Attarian S, Levy N, Nguyen K, Magdinier F, Roche S. Dysregulation of 4q35- and muscle-specific genes in fetuses with a short D4Z4 array linked to facio-scapulo-humeral dystrophy. Hum Mol Genet 2013; 22:4206-14. [PMID: 23777630 DOI: 10.1093/hmg/ddt272] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Facio-scapulo-humeral dystrophy (FSHD) results from deletions in the subtelomeric macrosatellite D4Z4 array on the 4q35 region. Upregulation of the DUX4 retrogene from the last D4Z4 repeated unit is thought to underlie FSHD pathophysiology. However, no one knows what triggers muscle defect and when alteration arises. To gain further insights into the molecular mechanisms of the disease, we evaluated at the molecular level, the perturbation linked to the FSHD genotype with no a priori on disease onset, severity or penetrance and prior to any infiltration by fibrotic or adipose tissue in biopsies from fetuses carrying a short pathogenic D4Z4 array (n = 6) compared with fetuses with a non-pathogenic D4Z4 array (n = 21). By measuring expression of several muscle-specific markers and 4q35 genes including the DUX4 retrogene by an RT-PCR and western blotting, we observed a global dysregulation of genes involved in myogenesis including MYOD1 in samples with <11 D4Z4. The DUX4-fl pathogenic transcript was detected in FSHD biopsies but also in controls. Importantly, in FSHD fetuses, we mainly detected the non-spliced DUX4-fl isoform. In addition, several other genes clustered at the 4q35 locus are upregulated in FSHD fetuses. Our study is the first to examine fetuses carrying an FSHD-linked genotype and reveals an extensive dysregulation of several muscle-specific and 4q35 genes at early development stage at a distance from any muscle defect. Overall, our work suggests that even if FSHD is an adult-onset muscular dystrophy, the disease might also involve early molecular defects arising during myogenesis or early differentiation.
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Affiliation(s)
- Natacha Broucqsault
- The authors wish it to be known that in their opinion the first two and the last two authors should be regarded as joint authors
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Giraud-Panis MJ, Pisano S, Benarroch-Popivker D, Pei B, Le Du MH, Gilson E. One identity or more for telomeres? Front Oncol 2013; 3:48. [PMID: 23509004 PMCID: PMC3598436 DOI: 10.3389/fonc.2013.00048] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Accepted: 02/23/2013] [Indexed: 12/19/2022] Open
Abstract
A major issue in telomere research is to understand how the integrity of chromosome ends is controlled. The fact that different types of nucleoprotein complexes have been described at the telomeres of different organisms raises the question of whether they have in common a structural identity that explains their role in chromosome protection. We will review here how telomeric nucleoprotein complexes are structured, comparing different organisms and trying to link these structures to telomere biology. It emerges that telomeres are formed by a complex and specific network of interactions between DNA, RNA, and proteins. The fact that these interactions and associated activities are reinforcing each other might help to guarantee the robustness of telomeric functions across the cell cycle and in the event of cellular perturbations. We will also discuss the recent notion that telomeres have evolved specific systems to overcome the DNA topological stress generated during their replication and transcription. This will lead to revisit the way we envisage the functioning of telomeric complexes since the regulation of topology is central to DNA stability, replication, recombination, and transcription as well as to chromosome higher-order organization.
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Affiliation(s)
- Marie-Josèphe Giraud-Panis
- Faculté de Médecine de Nice, Université de Nice-Sophia Antipolis, Institute for Research on Cancer and Aging Nice, UMR 7284 CNRS, U1081 INSERM Nice, France
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Bert SA, Robinson MD, Strbenac D, Statham AL, Song JZ, Hulf T, Sutherland RL, Coolen MW, Stirzaker C, Clark SJ. Regional activation of the cancer genome by long-range epigenetic remodeling. Cancer Cell 2013; 23:9-22. [PMID: 23245995 DOI: 10.1016/j.ccr.2012.11.006] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2012] [Revised: 05/24/2012] [Accepted: 11/15/2012] [Indexed: 10/27/2022]
Abstract
Epigenetic gene deregulation in cancer commonly occurs through chromatin repression and promoter hypermethylation of tumor-associated genes. However, the mechanism underpinning epigenetic-based gene activation in carcinogenesis is still poorly understood. Here, we identify a mechanism of domain gene deregulation through coordinated long-range epigenetic activation (LREA) of regions that typically span 1 Mb and harbor key oncogenes, microRNAs, and cancer biomarker genes. Gene promoters within LREA domains are characterized by a gain of active chromatin marks and a loss of repressive marks. Notably, although promoter hypomethylation is uncommon, we show that extensive DNA hypermethylation of CpG islands or "CpG-island borders" is strongly related to cancer-specific gene activation or differential promoter usage. These findings have wide ramifications for cancer diagnosis, progression, and epigenetic-based gene therapies.
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Affiliation(s)
- Saul A Bert
- Cancer Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales 2010, Australia
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40
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Arancio W, Giordano C, Pizzolanti G. A ceRNA analysis on LMNA gene focusing on the Hutchinson-Gilford progeria syndrome. J Clin Bioinforma 2013; 3:2. [PMID: 23317481 PMCID: PMC3563501 DOI: 10.1186/2043-9113-3-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Accepted: 01/07/2013] [Indexed: 02/08/2023] Open
Abstract
UNLABELLED BACKGROUND Hutchinson-Gilford progeria syndrome is a rare dominant human disease of genetic origin. The average life expectancy is about 20 years, patients' life quality is still very poor and no efficient therapy has yet been developed. It is caused by mutation of the LMNA gene, which results in accumulation in the nuclear membrane of a particular splicing form of Lamin-A called progerin. The mechanism by which progerin perturbs cellular homeostasis and leads to the symptoms is still under debate.Micro-RNAs are able to negatively regulate transcription by coupling with the 3' UnTranslated Region of messenger RNAs. Several Micro-RNAs recognize the same 3' UnTranslated Region and each Micro-RNA can recognize multiple 3' UnTranslated Regions of different messenger RNAs. When different messenger RNAs are co-regulated via a similar panel of micro-RNAs, these messengers are called Competing Endogenous RNAs, or ceRNAs.The 3' UnTranslated Region of the longest LMNA transcript was analysed looking for its ceRNAs. The aim of this study was to search for candidate genes and gene ontology functions possibly influenced by LMNA mutations that may exert a role in progeria development. RESULTS 11 miRNAs were isolated as potential LMNA regulators. By computational analysis, the miRNAs pointed to 17 putative LMNA ceRNAs. Gene ontology analysis of isolated ceRNAs showed an enrichment in RNA interference and control of cell cycle functions. CONCLUSION This study isolated novel genes and functions potentially involved in LMNA network of regulation that could be involved in laminopathies such as the Hutchinson-Gilford progeria syndrome.
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Affiliation(s)
- Walter Arancio
- Section of Endocrinology, Diabetology & Metabolism, Dipartimento Biomedico di Medicina Interna e Specialistica (Di,Bi,M,I,S,), University of Palermo, Piazza delle Cliniche 2, Palermo, 90127, Italy.
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Hartweck LM, Anderson LJ, Lemmers RJ, Dandapat A, Toso EA, Dalton JC, Tawil R, Day JW, van der Maarel SM, Kyba M. A focal domain of extreme demethylation within D4Z4 in FSHD2. Neurology 2013; 80:392-9. [PMID: 23284062 DOI: 10.1212/wnl.0b013e31827f075c] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disease with an unclear genetic mechanism. Most patients have a contraction of the D4Z4 macrosatellite repeat array at 4qter, which is thought to cause partial demethylation (FSHD1) of the contracted allele. Demethylation has been surveyed at 3 restriction enzyme sites in the first repeat and only a single site across the entire array, and current models postulate that a generalized D4Z4 chromatin alteration causes FSHD. The background of normal alleles has confounded the study of epigenetic alterations; however, rare patients (FSHD2) have a form of the disease in which demethylation is global, i.e., on all D4Z4 elements throughout the genome. Our objective was to take advantage of the global nature of FSHD2 to identify where disease-relevant methylation changes occur within D4Z4. METHODS Using bisulfite sequencing of DNA from blood and myoblast cells, methylation levels at 74 CpG sites across 3 disparate regions within D4Z4 were measured in FSHD2 patients and controls. RESULTS We found that rates of demethylation caused by FSHD2 are not consistent across D4Z4. We identified a focal region of extreme demethylation within a 5' domain, which we named DR1. Other D4Z4 regions, including the DUX4 ORF, were hypomethylated but to a much lesser extent. CONCLUSIONS These data challenge the simple view that FSHD is caused by a broad "opening" of D4Z4 and lead us to postulate that the region of focal demethylation is the site of action of the key D4Z4 chromatin regulatory factors that go awry in FSHD.
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Affiliation(s)
- Lynn M Hartweck
- Department of Pediatrics and Lillehei Heart Institute, Minneapolis, MN, USA
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Deng Z, Wang Z, Stong N, Plasschaert R, Moczan A, Chen HS, Hu S, Wikramasinghe P, Davuluri RV, Bartolomei MS, Riethman H, Lieberman PM. A role for CTCF and cohesin in subtelomere chromatin organization, TERRA transcription, and telomere end protection. EMBO J 2012; 31:4165-78. [PMID: 23010778 PMCID: PMC3492729 DOI: 10.1038/emboj.2012.266] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Accepted: 08/29/2012] [Indexed: 01/04/2023] Open
Abstract
The contribution of human subtelomeric DNA and chromatin organization to telomere integrity and chromosome end protection is not yet understood in molecular detail. Here, we show by ChIP-Seq that most human subtelomeres contain a CTCF- and cohesin-binding site within ∼1-2 kb of the TTAGGG repeat tract and adjacent to a CpG-islands implicated in TERRA transcription control. ChIP-Seq also revealed that RNA polymerase II (RNAPII) was enriched at sites adjacent to the CTCF sites and extending towards the telomere repeat tracts. Mutation of CTCF-binding sites in plasmid-borne promoters reduced transcriptional activity in an orientation-dependent manner. Depletion of CTCF by shRNA led to a decrease in TERRA transcription, and a loss of cohesin and RNAPII binding to the subtelomeres. Depletion of either CTCF or cohesin subunit Rad21 caused telomere-induced DNA damage foci (TIF) formation, and destabilized TRF1 and TRF2 binding to the TTAGGG proximal subtelomere DNA. These findings indicate that CTCF and cohesin are integral components of most human subtelomeres, and important for the regulation of TERRA transcription and telomere end protection.
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Affiliation(s)
- Zhong Deng
- The Wistar Institute, Philadelphia, PA, USA
| | - Zhuo Wang
- The Wistar Institute, Philadelphia, PA, USA
| | - Nick Stong
- The Wistar Institute, Philadelphia, PA, USA
| | - Robert Plasschaert
- Cell and Developmental Biology Department, University of Pennsylvania, Philadelphia, PA, USA
| | | | | | - Sufeng Hu
- The Wistar Institute, Philadelphia, PA, USA
| | | | | | - Marisa S Bartolomei
- Cell and Developmental Biology Department, University of Pennsylvania, Philadelphia, PA, USA
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Muck JS, Kandasamy K, Englmann A, Günther M, Zink D. Perinuclear positioning of the inactive human cystic fibrosis gene depends on CTCF, A-type lamins and an active histone deacetylase. J Cell Biochem 2012; 113:2607-21. [PMID: 22422629 DOI: 10.1002/jcb.24136] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The nuclear positioning of mammalian genes often correlates with their functional state. For instance, the human cystic fibrosis transmembrane conductance regulator (CFTR) gene associates with the nuclear periphery in its inactive state, but occupies interior positions when active. It is not understood how nuclear gene positioning is determined. Here, we investigated trichostatin A (TSA)-induced repositioning of CFTR in order to address molecular mechanisms controlling gene positioning. Treatment with the histone deacetylase (HDAC) inhibitor TSA induced increased histone acetylation and CFTR repositioning towards the interior within 20 min. When CFTR localized in the nuclear interior (either after TSA treatment or when the gene was active) consistent histone H3 hyperacetylation was observed at a CTCF site close to the CFTR promoter. Knockdown experiments revealed that CTCF was essential for perinuclear CFTR positioning and both, CTCF knockdown as well as TSA treatment had similar and CFTR-specific effects on radial positioning. Furthermore, knockdown experiments revealed that also A-type lamins were required for the perinuclear positioning of CFTR. Together, the results showed that CTCF, A-type lamins and an active HDAC were essential for perinuclear positioning of CFTR and these components acted on a CTCF site adjacent to the CFTR promoter. The results are consistent with the idea that CTCF bound close to the CFTR promoter, A-type lamins and an active HDAC form a complex at the nuclear periphery, which becomes disrupted upon inhibition of the HDAC, leading to the observed release of CFTR.
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Affiliation(s)
- Joscha S Muck
- Institute of Bioengineering and Nanotechnology (IBN), Department of Cell and Tissue Engineering, 31 Biopolis Way, The Nanos, Singapore 138669
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Méjat A, Misteli T. LINC complexes in health and disease. Nucleus 2012; 1:40-52. [PMID: 21327104 DOI: 10.4161/nucl.1.1.10530] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 11/04/2009] [Accepted: 11/05/2009] [Indexed: 11/19/2022] Open
Abstract
The cell nucleus communicates with the rest of the cell via nucleo/cytoplasmic transport of proteins and RNA through the nuclear pores. Direct mechanical links between the nucleus and the cytoplasm have recently emerged in the form of LINC (Linkers of the nucleoskeleton to the cytoskeleton) protein complexes. A LINC complex consists of four components. At its core are an inner nuclear membrane (INM) transmembrane protein and an outer nuclear membrane (ONM) transmembrane protein which physically interact with each other in the lumen of the NE. The INM LINC component interacts on the nucleoplasmic side with either the lamina or with an INM-associated protein. The ONM LINC component on the other hand contacts on the cytoplasmatic side a component of the cytoskeleton. This review highlights the components of LINC complexes and their emerging roles in mechanotransduction, nuclear migration, chromosome positioning, signaling, meiosis, cytoskeletal organization and human disease.
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Affiliation(s)
- Alexandre Méjat
- National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
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Ottaviani A, Schluth-Bolard C, Gilson E, Magdinier F. D4Z4 as a prototype of CTCF and lamins-dependent insulator in human cells. Nucleus 2012; 1:30-6. [PMID: 21327102 DOI: 10.4161/nucl.1.1.10799] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Revised: 11/12/2009] [Accepted: 11/16/2009] [Indexed: 12/21/2022] Open
Abstract
Using cellular models that mimic the organizations of the subtelomeric 4q35 locus found in patients affected with Facio-Scapulo-Humeral Dystrophy (FSHD) and in healthy individuals, we recently investigated the biological function of the D4Z4 macrosatellite in this subtelomeric context.We demonstrated that D4Z4 acts as a CTCF and A-type lamins dependent insulator element exhibiting both enhancer- blocking and barrier activities, and displaces a telomere towards the nuclear periphery. This peripheral positioning activity lies within a short sequence that interacts with CTCF and A-type lamins. Depletion in either of these two proteins suppresses these perinuclear activities, revealing the existence of a subtelomeric sequence that is sufficient to position an adjacent telomere to the nuclear periphery. We discuss here the biological implications of these results in the light of our current knowledge in related fields and the potential implication of other CTCF and A-type lamins insulators in the light of human pathologies.
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Affiliation(s)
- Alexandre Ottaviani
- Laboratoire de Biologie Moléculaire de la Cellule, CNRS UMR5239, Ecole Normale Supérieure de Lyon, UCBL1, Lyon, France
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Lanzuolo C. Epigenetic alterations in muscular disorders. Comp Funct Genomics 2012; 2012:256892. [PMID: 22761545 PMCID: PMC3385594 DOI: 10.1155/2012/256892] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Revised: 04/11/2012] [Accepted: 04/19/2012] [Indexed: 11/18/2022] Open
Abstract
Epigenetic mechanisms, acting via chromatin organization, fix in time and space different transcriptional programs and contribute to the quality, stability, and heritability of cell-specific transcription programs. In the last years, great advances have been made in our understanding of mechanisms by which this occurs in normal subjects. However, only a small part of the complete picture has been revealed. Abnormal gene expression patterns are often implicated in the development of different diseases, and thus epigenetic studies from patients promise to fill an important lack of knowledge, deciphering aberrant molecular mechanisms at the basis of pathogenesis and diseases progression. The identification of epigenetic modifications that could be used as targets for therapeutic interventions could be particularly timely in the light of pharmacologically reversion of pathological perturbations, avoiding changes in DNA sequences. Here I discuss the available information on epigenetic mechanisms that, altered in neuromuscular disorders, could contribute to the progression of the disease.
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Affiliation(s)
- Chiara Lanzuolo
- CNR Institute of Cellular Biology and Neurobiology, IRCCS Santa Lucia Foundation, Via Del Fosso di Fiorano 64, 00143 Rome, Italy
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Neguembor MV, Gabellini D. In junk we trust: repetitive DNA, epigenetics and facioscapulohumeral muscular dystrophy. Epigenomics 2012; 2:271-87. [PMID: 22121874 DOI: 10.2217/epi.10.8] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant myopathy with a peculiar etiology. Unlike most genetic disorders, FSHD is not caused by mutations in a protein-coding gene. Instead, it is associated with contraction of the D4Z4 macrosatellite repeat array located at 4q35. Interestingly, D4Z4 deletion is not sufficient per se to cause FSHD. Moreover, the disease severity, its rate of progression and the distribution of muscle weakness display great variability even among close family relatives. Hence, additional genetic and epigenetic events appear to be required for FSHD pathogenesis. Indeed, recent findings suggest that virtually all levels of epigenetic regulation, from DNA methylation to higher order chromosomal architecture, exhibit alterations in the disease locus causing deregulation of 4q35 gene expression, ultimately leading to FSHD.
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Affiliation(s)
- Maria V Neguembor
- International PhD Program in Cellular & Molecular Biology, Vita-Salute San Raffaele University, Milan, Italy
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Telomeres and the nucleus. Semin Cancer Biol 2012; 23:116-24. [PMID: 22330096 DOI: 10.1016/j.semcancer.2012.02.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 02/01/2012] [Accepted: 02/02/2012] [Indexed: 01/08/2023]
Abstract
Telomeres are crucial for the maintenance of genome stability through "capping" of chromosome ends to prevent their recognition as double-strand breaks, thus avoiding end-to-end fusions or illegitimate recombination [1-3]. Similar to other genomic regions, telomeres participate to the nuclear architecture while being highly mobile. The interaction of telomeres with nuclear domains or compartments greatly differs not only between organisms but also between cells within the same organism. It is also expected that biological processes like replication, repair or telomere elongation impact the distribution of chromosome extremities within the nucleus, as they probably do with other regions of the genome. Pathological processes such as cancer induce profound changes in the nuclear architecture, which also affects telomere dynamics and spatial organization. Here we will expose our present knowledge on the relationship between telomeres and nuclear architecture and on how this relationship is affected by normal or abnormal telomere metabolisms.
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Raab JR, Chiu J, Zhu J, Katzman S, Kurukuti S, Wade PA, Haussler D, Kamakaka RT. Human tRNA genes function as chromatin insulators. EMBO J 2011; 31:330-50. [PMID: 22085927 DOI: 10.1038/emboj.2011.406] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 10/07/2011] [Indexed: 11/09/2022] Open
Abstract
Insulators help separate active chromatin domains from silenced ones. In yeast, gene promoters act as insulators to block the spread of Sir and HP1 mediated silencing while in metazoans most insulators are multipartite autonomous entities. tDNAs are repetitive sequences dispersed throughout the human genome and we now show that some of these tDNAs can function as insulators in human cells. Using computational methods, we identified putative human tDNA insulators. Using silencer blocking, transgene protection and repressor blocking assays we show that some of these tDNA-containing fragments can function as barrier insulators in human cells. We find that these elements also have the ability to block enhancers from activating RNA pol II transcribed promoters. Characterization of a putative tDNA insulator in human cells reveals that the site possesses chromatin signatures similar to those observed at other better-characterized eukaryotic insulators. Enhanced 4C analysis demonstrates that the tDNA insulator makes long-range chromatin contacts with other tDNAs and ETC sites but not with intervening or flanking RNA pol II transcribed genes.
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Affiliation(s)
- Jesse R Raab
- Department of MCD Biology, University of California, Santa Cruz, CA, USA
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Abstract
Chromatin insulators are DNA-protein complexes with broad functions in nuclear biology. Based on the ability of insulator proteins to interact with each other, it was originally found that insulators form loops that bring together distant regions of the genome. Data from genome-wide localization studies indicate that insulator proteins can be present in intergenic regions as well as at the 5', introns or 3' of genes, suggesting a variety of roles for insulator loops in chromosome biology. Recent results suggest that insulators mediate intra- and interchromosomal interactions to affect transcription, imprinting, and recombination. Cells have developed mechanisms to control insulator activity by recruiting specialized proteins or by covalent modification of core components. It is then possible that insulator-mediated interactions set up cell-specific blueprints of nuclear organization that may contribute to the establishment of different patterns of gene expression during cell differentiation and development. As a consequence, disruption of insulator activity could result in the development of cancer or other disease states.
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Affiliation(s)
- Jingping Yang
- Department of Biology, Emory University, Atlanta, GA, USA
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