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Gong Y, Liu Y. R-Loops at Chromosome Ends: From Formation, Regulation, and Cellular Consequence. Cancers (Basel) 2023; 15:cancers15072178. [PMID: 37046839 PMCID: PMC10093737 DOI: 10.3390/cancers15072178] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 04/03/2023] [Accepted: 04/04/2023] [Indexed: 04/14/2023] Open
Abstract
Telomeric repeat containing RNA (TERRA) is transcribed from subtelomeric regions to telomeres. TERRA RNA can invade telomeric dsDNA and form telomeric R-loop structures. A growing body of evidence suggests that TERRA-mediated R-loops are critical players in telomere length homeostasis. Here, we will review current knowledge on the regulation of R-loop levels at telomeres. In particular, we will discuss how the central player TERRA and its binding proteins modulate R-loop levels through various mechanisms. We will further provide an overview of the consequences of TERRA-mediated persistent or unscheduled R-loops at telomeres in human ALT cancers and other organisms, with a focus on telomere length regulation after replication interference-induced damage and DNA homologous recombination-mediated repair.
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Affiliation(s)
- Yi Gong
- Laboratory of Genetics and Genomics, National Institute on Aging/National Institutes of Health, 251 Bayview Blvd, Baltimore, MD 21224, USA
| | - Yie Liu
- Laboratory of Genetics and Genomics, National Institute on Aging/National Institutes of Health, 251 Bayview Blvd, Baltimore, MD 21224, USA
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2
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Pappalardo XG, Barra V. Losing DNA methylation at repetitive elements and breaking bad. Epigenetics Chromatin 2021; 14:25. [PMID: 34082816 PMCID: PMC8173753 DOI: 10.1186/s13072-021-00400-z] [Citation(s) in RCA: 57] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Accepted: 05/21/2021] [Indexed: 02/08/2023] Open
Abstract
Background DNA methylation is an epigenetic chromatin mark that allows heterochromatin formation and gene silencing. It has a fundamental role in preserving genome stability (including chromosome stability) by controlling both gene expression and chromatin structure. Therefore, the onset of an incorrect pattern of DNA methylation is potentially dangerous for the cells. This is particularly important with respect to repetitive elements, which constitute the third of the human genome. Main body Repetitive sequences are involved in several cell processes, however, due to their intrinsic nature, they can be a source of genome instability. Thus, most repetitive elements are usually methylated to maintain a heterochromatic, repressed state. Notably, there is increasing evidence showing that repetitive elements (satellites, long interspersed nuclear elements (LINEs), Alus) are frequently hypomethylated in various of human pathologies, from cancer to psychiatric disorders. Repetitive sequences’ hypomethylation correlates with chromatin relaxation and unscheduled transcription. If these alterations are directly involved in human diseases aetiology and how, is still under investigation. Conclusions Hypomethylation of different families of repetitive sequences is recurrent in many different human diseases, suggesting that the methylation status of these elements can be involved in preservation of human health. This provides a promising point of view towards the research of therapeutic strategies focused on specifically tuning DNA methylation of DNA repeats.
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Affiliation(s)
- Xena Giada Pappalardo
- Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95125, Catania, Italy.,National Council of Research, Institute for Biomedical Research and Innovation (IRIB), Unit of Catania, 95125, Catania, Italy
| | - Viviana Barra
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), University of Palermo, 90128, Palermo, Italy.
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3
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Samra N, Toubiana S, Yttervik H, Tzur-Gilat A, Morani I, Itzkovich C, Giladi L, Abu Jabal K, Cao JZ, Godley LA, Mory A, Baris Feldman H, Tveten K, Selig S, Weiss K. RBL2 bi-allelic truncating variants cause severe motor and cognitive impairment without evidence for abnormalities in DNA methylation or telomeric function. J Hum Genet 2021; 66:1101-1112. [PMID: 33980986 DOI: 10.1038/s10038-021-00931-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 04/14/2021] [Accepted: 04/14/2021] [Indexed: 02/01/2023]
Abstract
RBL2/p130, a member of the retinoblastoma family of proteins, is a key regulator of cell division and propagates irreversible senescence. RBL2/p130 is also involved in neuronal differentiation and survival, and eliminating Rbl2 in certain mouse strains leads to embryonic lethality accompanied by an abnormal central nervous system (CNS) phenotype. Conflicting reports exist regarding a role of RBL2/p130 in transcriptional regulation of DNA methyltransferases (DNMTs), as well as the control of telomere length. Here we describe the phenotype of three patients carrying bi-allelic RBL2-truncating variants. All presented with infantile hypotonia, severe developmental delay and microcephaly. Malignancies were not reported in carriers or patients. Previous studies carried out on mice and human cultured cells, associated RBL2 loss to DNA methylation and telomere length dysregulation. Here, we investigated whether patient cells lacking RBL2 display related abnormalities. The study of primary patient fibroblasts did not detect abnormalities in expression of DNMTs. Furthermore, methylation levels of whole genome DNA, and specifically of pericentromeric repeats and subtelomeric regions, were unperturbed. RBL2-null fibroblasts show no evidence for abnormal elongation by telomeric recombination. Finally, gradual telomere shortening, and normal onset of senescence were observed following continuous culturing of RBL2-mutated fibroblasts. Thus, this study resolves uncertainties regarding a potential non-redundant role for RBL2 in DNA methylation and telomere length regulation, and indicates that loss of function variants in RBL2 cause a severe autosomal recessive neurodevelopmental disorder in humans.
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Affiliation(s)
- Nadra Samra
- Genetic Unit, Ziv Medical Center, Tzfat, Israel.,Faculty of Medicine, Bar Ilan University, Tzfat, Israel
| | - Shir Toubiana
- Department of Genetics and Developmental Biology, The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Hilde Yttervik
- Department of Medical Genetics, University Hospital of North Norway, Tromsø, Norway
| | - Aya Tzur-Gilat
- Department of Genetics and Developmental Biology, The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | | | - Chen Itzkovich
- The Clinical Research Institute at Rambam Health Care Campus, Haifa, Israel
| | - Liran Giladi
- Department of Genetics and Developmental Biology, The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | | | - John Z Cao
- Section of Hematology Oncology, Departments of Medicine and Human Genetics, The University of Chicago, Chicago, IL, USA
| | - Lucy A Godley
- Section of Hematology Oncology, Departments of Medicine and Human Genetics, The University of Chicago, Chicago, IL, USA
| | - Adi Mory
- The Genetics Institute, Rambam Health Care Campus, Haifa, Israel.,The Genetics Institute, Tel Aviv Sourasky Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Hagit Baris Feldman
- The Genetics Institute, Rambam Health Care Campus, Haifa, Israel.,The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.,The Genetics Institute, Tel Aviv Sourasky Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Kristian Tveten
- Department of Medical Genetics, Telemark Hospital Trust, Skien, Norway
| | - Sara Selig
- Department of Genetics and Developmental Biology, The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel. .,Laboratory of Molecular Medicine, Rambam Health Care Campus, Haifa, Israel.
| | - Karin Weiss
- The Genetics Institute, Rambam Health Care Campus, Haifa, Israel.,The Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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4
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Toubiana S, Larom G, Smoom R, Duszynski RJ, Godley LA, Francastel C, Velasco G, Selig S. Regulation of telomeric function by DNA methylation differs between humans and mice. Hum Mol Genet 2020; 29:3197-3210. [PMID: 32916696 DOI: 10.1093/hmg/ddaa206] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 09/02/2020] [Accepted: 09/04/2020] [Indexed: 11/13/2022] Open
Abstract
The most distal 2 kb region in the majority of human subtelomeres contains CpG-rich promoters for TERRA, a long non-coding RNA. When the function of the de novo DNA methyltransferase DNMT3B is disrupted, as in ICF1 syndrome, subtelomeres are abnormally hypomethylated, subtelomeric heterochromatin acquires open chromatin characteristics, TERRA is highly expressed, and telomeres shorten rapidly. In this study, we explored whether the regulation of subtelomeric epigenetic characteristics by DNMT3B is conserved between humans and mice. Studying the DNA sequence of the distal 30 kb of the majority of murine q-arm subtelomeres indicated that these regions are relatively CpG-poor and do not contain TERRA promoters similar to those present in humans. Despite the lack of human-like TERRA promoters, we clearly detected TERRA expression originating from at least seven q-arm subtelomeres, and at higher levels in mouse pluripotent stem cells in comparison with mouse embryonic fibroblasts (MEFs). However, these differences in TERRA expression could not be explained by differential methylation of CpG islands present in the TERRA-expressing murine subtelomeres. To determine whether Dnmt3b regulates the expression of TERRA in mice, we characterized subtelomeric methylation and associated telomeric functions in cells derived from ICF1 model mice. Littermate-derived WT and ICF1 MEFs demonstrated no significant differences in subtelomeric DNA methylation, chromatin modifications, TERRA expression levels, telomere sister chromatid exchange or telomere length. We conclude that the epigenetic characteristics of murine subtelomeres differ substantially from their human counterparts and that TERRA transcription in mice is regulated by factors others than Dnmt3b.
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Affiliation(s)
- Shir Toubiana
- Department of Genetics, Rappaport Faculty of Medicine and Research Institute, Technion, Haifa 31096, Israel
| | - Gal Larom
- Department of Genetics, Rappaport Faculty of Medicine and Research Institute, Technion, Haifa 31096, Israel
| | - Riham Smoom
- Department of Genetics, The Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Robert J Duszynski
- Department of Medicine, Section of Hematology Oncology, The University of Chicago, Chicago 60637, USA
| | - Lucy A Godley
- Department of Medicine, Section of Hematology Oncology, The University of Chicago, Chicago 60637, USA
| | - Claire Francastel
- Université de Paris, Epigénétique et Destin Cellulaire, CNRS, Paris 75013, France
| | - Guillaume Velasco
- Université de Paris, Epigénétique et Destin Cellulaire, CNRS, Paris 75013, France
| | - Sara Selig
- Department of Genetics, Rappaport Faculty of Medicine and Research Institute, Technion, Haifa 31096, Israel
- Laboratory of Molecular Medicine, Rambam Health Care Campus, Haifa 31096, Israel
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5
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Toubiana S, Gagliardi M, Papa M, Manco R, Tzukerman M, Matarazzo MR, Selig S. Persistent epigenetic memory impedes rescue of the telomeric phenotype in human ICF iPSCs following DNMT3B correction. eLife 2019; 8:e47859. [PMID: 31738163 PMCID: PMC6897513 DOI: 10.7554/elife.47859] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 11/17/2019] [Indexed: 12/15/2022] Open
Abstract
DNA methyltransferase 3B (DNMT3B) is the major DNMT that methylates mammalian genomes during early development. Mutations in human DNMT3B disrupt genome-wide DNA methylation patterns and result in ICF syndrome type 1 (ICF1). To study whether normal DNA methylation patterns may be restored in ICF1 cells, we corrected DNMT3B mutations in induced pluripotent stem cells from ICF1 patients. Focusing on repetitive regions, we show that in contrast to pericentromeric repeats, which reacquire normal methylation, the majority of subtelomeres acquire only partial DNA methylation and, accordingly, the ICF1 telomeric phenotype persists. Subtelomeres resistant to de novo methylation were characterized by abnormally high H3K4 trimethylation (H3K4me3), and short-term reduction of H3K4me3 by pharmacological intervention partially restored subtelomeric DNA methylation. These findings demonstrate that the abnormal epigenetic landscape established in ICF1 cells restricts the recruitment of DNMT3B, and suggest that rescue of epigenetic diseases with genome-wide disruptions will demand further manipulation beyond mutation correction.
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Affiliation(s)
- Shir Toubiana
- Molecular Medicine LaboratoryRappaport Faculty of Medicine, TechnionHaifaIsrael
- Rambam Health Care CampusHaifaIsrael
| | | | | | - Roberta Manco
- Institute of Genetics and Biophysics, ABT CNRNaplesItaly
| | - Maty Tzukerman
- Molecular Medicine LaboratoryRappaport Faculty of Medicine, TechnionHaifaIsrael
- Rambam Health Care CampusHaifaIsrael
| | | | - Sara Selig
- Molecular Medicine LaboratoryRappaport Faculty of Medicine, TechnionHaifaIsrael
- Rambam Health Care CampusHaifaIsrael
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6
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Hu H, Chen C, Shi S, Li B, Duan S. The gene mutations and subtelomeric DNA methylation in immunodeficiency, centromeric instability and facial anomalies syndrome. Autoimmunity 2019; 52:192-198. [PMID: 31476899 DOI: 10.1080/08916934.2019.1657846] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Immunodeficiency, centromeric instability and facial anomalies syndrome (ICF) is a rare autosomal recessive disorder, which is characteristic of a severe impairment of immunity. In the genetic aspect, ICF is featured with mutations primarily located in the specific genes (DNMT3B for ICF1, ZBTB24 for ICF2, CDCA7 for ICF3, and HELLS for ICF4). The subtelomeric region is defined as 500 kb at the terminal of each autosomal arm. And subtelomeric DNA fragments can partially regulate key biological activities, including chromosome movement and localization in the nucleus. In this review, we updated and summarized gene mutations in ICF based on the previous review. In addition, we focused on the correlation between subtelomeric DNA methylation and ICF. The relationship between subtelomeric methylation and telomere length in ICF was also summarized.
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Affiliation(s)
- Haochang Hu
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Chujia Chen
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Shanping Shi
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Bin Li
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Shiwei Duan
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
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7
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Fang Z, Pan Z. Essential Role of Ubiquitin-Fold Modifier 1 Conjugation in DNA Damage Response. DNA Cell Biol 2019; 38:1030-1039. [PMID: 31368785 DOI: 10.1089/dna.2019.4861] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Both endogenous and exogenous factors can cause DNA damage that compromises genomic integrity and cell viability. A proper DNA damage response (DDR) plays a role in maintaining genome stability and preventing tumorigenesis. DNA double-strand breaks (DSBs) are the most toxic DNA lesion, whose response is dominated by the ataxia-telangiectasia mutated (ATM) protein kinase. After being activated by the sensor Mre11-Rad50-Nbs1 (MRN) complex or acetyltransferase Tip60, ATM rapidly phosphorylates downstream targets to launch DDR signaling when DNA is damaged. However, the exact mechanism of DDR is complex and ambiguous. Ufmylation, one type of ubiquitin-like modification, proceeds mainly through a three-step enzymatic reaction to help ubiquitin-fold modifier 1 (Ufm1), attach to substrates with ubiquitin-like modifier-activating enzyme 5 (Uba5), Ufm1-conjugating enzyme 1 (Ufc1) and Ufm1-specific ligase 1 (Ufl1). Although ubiquitination is essential to the DSBs response, the potential function of ufmylation in DDR is largely unknown. Herein, we review the relationship between ufmylation and DDR to elucidate the function and mechanism of ufmylation in DDR, which would reveal the pathogenesis of some diseases and provide new guidance to create a therapeutic method.
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Affiliation(s)
- Zhi Fang
- Jiangxi Medical College, Nanchang University, Nanchang, China
| | - Zezheng Pan
- Faculty of Basic Medical Science, Jiangxi Medical College, Nanchang University, Nanchang, China
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8
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Toubiana S, Velasco G, Chityat A, Kaindl AM, Hershtig N, Tzur-Gilat A, Francastel C, Selig S. Subtelomeric methylation distinguishes between subtypes of Immunodeficiency, Centromeric instability and Facial anomalies syndrome. Hum Mol Genet 2018; 27:3568-3581. [PMID: 30010917 DOI: 10.1093/hmg/ddy265] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Accepted: 07/11/2018] [Indexed: 12/16/2022] Open
Abstract
Human telomeres and adjacent subtelomeres are packaged as heterochromatin. Subtelomeric DNA undergoes methylation during development by DNA methyltransferase 3B (DNMT3B), including the CpG-rich promoters of the long non-coding RNA (TERRA) embedded in these regions. The factors that direct DNMT3B methylation to human subtelomeres and maintain this methylation throughout lifetime are yet unknown. The importance of subtelomeric methylation is manifested through the abnormal telomeric phenotype in Immunodeficiency, Centromeric instability and Facial anomalies (ICF) syndrome type 1 patients carrying mutations in DNMT3B. Patient cells demonstrate subtelomeric hypomethylation, accompanied by elevated TERRA transcription, accelerated telomere shortening and premature senescence of fibroblasts. ICF syndrome can arise due to mutations in at least three additional genes, ZBTB24 (ICF2), CDCA7 (ICF3) and HELLS (ICF4). While pericentromeric repeat hypomethylation is evident in all ICF syndrome subtypes, the status of subtelomeric DNA methylation had not been described for patients of subtypes 2-4. Here we explored the telomeric phenotype in cells derived from ICF2-4 patients with the aim to determine whether ZBTB24, CDCA7 and HELLS also play a role in establishing and/or maintaining human subtelomeric methylation. We found normal subtelomeric methylation in ICF2-4 and accordingly low TERRA levels and unperturbed telomere length. Moreover, depleting the ICF2-4-related proteins in normal fibroblasts did not influence subtelomeric methylation. Thus, these gene products are not involved in establishing or maintaining subtelomeric methylation. Our findings indicate that human subtelomeric heterochromatin has specialized methylation regulation and highlight the telomeric phenotype as a characteristic that distinguishes ICF1 from ICF2-4.
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Affiliation(s)
- Shir Toubiana
- Molecular Medicine Laboratory, Rambam Health Care Campus and Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Guillaume Velasco
- Université Paris Diderot, Sorbonne Paris Cité, Epigenetics and Cell Fate, CNRS, Paris Cedex, France
| | - Adi Chityat
- Molecular Medicine Laboratory, Rambam Health Care Campus and Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Angela M Kaindl
- Charité - Universitätsmedizin Berlin, Department of Pediatric Neurology, Center for Chronically Sick Children, Institute of Cell Biology and Neurobiology, Augustenburger Platz 1, Berlin, Germany
| | | | - Aya Tzur-Gilat
- Molecular Medicine Laboratory, Rambam Health Care Campus and Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Claire Francastel
- Université Paris Diderot, Sorbonne Paris Cité, Epigenetics and Cell Fate, CNRS, Paris Cedex, France
| | - Sara Selig
- Molecular Medicine Laboratory, Rambam Health Care Campus and Rappaport Faculty of Medicine, Technion, Haifa, Israel
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9
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Toubiana S, Selig S. DNA:RNA hybrids at telomeres - when it is better to be out of the (R) loop. FEBS J 2018; 285:2552-2566. [PMID: 29637701 DOI: 10.1111/febs.14464] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 03/11/2018] [Accepted: 04/03/2018] [Indexed: 01/31/2023]
Abstract
R-loops (RLs) are three-stranded nucleic acid structures that contain a DNA:RNA hybrid and a displaced DNA strand. Genomic regions with GC skew and a G-rich transcript are particularly prone to form RLs. RLs play important physiological roles in cells; however, when present at abnormally high levels, they may threaten genome stability. The perfect GC skew of telomeric repeats and the discovery of telomeric repeat-containing RNA (TERRA), a long noncoding transcript that consists of the G-rich telomeric sequence, make telomeric sequences the perfect candidates for generating RLs. Indeed, in the past 5 years, telomere R-loops (TRLs) have been demonstrated in Saccharomyces cerevisiae, Trypanosoma brucei, and human cells. The presence of TRLs in normal human cells that transcribe low levels of TERRA, suggests a physiological role for these nucleic structures in telomere maintenance. Abnormally enhanced TERRA transcription, as found in several human pathological conditions, leads to high TRL levels and various cellular outcomes, depending on the recombinogenic capabilities of the cells. Study of TRLs in various organisms highlights the necessity for tight regulation of these structures, which can switch from beneficial to detrimental under different conditions. Here, we review the current state of knowledge on TRLs, describe several means by which TRLs are regulated, and discuss how findings from yeast are relevant to human pathological scenarios in which TRLs are deregulated.
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Affiliation(s)
- Shir Toubiana
- Molecular Medicine Laboratory, Rappaport Faculty of Medicine, Rambam Health Care Campus, Technion, Haifa, Israel
| | - Sara Selig
- Molecular Medicine Laboratory, Rappaport Faculty of Medicine, Rambam Health Care Campus, Technion, Haifa, Israel
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