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Olivier M, Hesketh A, Pouch-Pélissier MN, Pélissier T, Huang Y, Latrasse D, Benhamed M, Mathieu O. RTEL1 is required for silencing and epigenome stability. Nucleic Acids Res 2023; 51:8463-8479. [PMID: 37471026 PMCID: PMC10484728 DOI: 10.1093/nar/gkad610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 06/13/2023] [Accepted: 07/10/2023] [Indexed: 07/21/2023] Open
Abstract
Transcriptional silencing is an essential mechanism for controlling the expression of genes, transgenes and heterochromatic repeats through specific epigenetic marks on chromatin that are maintained during DNA replication. In Arabidopsis, silenced transgenes and heterochromatic sequences are typically associated with high levels of DNA methylation, while silenced genes are enriched in H3K27me3. Reactivation of these loci is often correlated with decreased levels of these repressive epigenetic marks. Here, we report that the DNA helicase REGULATOR OF TELOMERE ELONGATION 1 (RTEL1) is required for transcriptional silencing. RTEL1 deficiency causes upregulation of many genes enriched in H3K27me3 accompanied by a moderate decrease in this mark, but no loss of DNA methylation at reactivated heterochromatic loci. Instead, heterochromatin exhibits DNA hypermethylation and increased H3K27me3 in rtel1. We further find that loss of RTEL1 suppresses the release of heterochromatin silencing caused by the absence of the MOM1 silencing factor. RTEL1 is conserved among eukaryotes and plays a key role in resolving DNA secondary structures during DNA replication. Inducing such aberrant DNA structures using DNA cross-linking agents also results in a loss of transcriptional silencing. These findings uncover unappreciated roles for RTEL1 in transcriptional silencing and in stabilizing DNA methylation and H3K27me3 patterns.
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Affiliation(s)
- Margaux Olivier
- Institute of Genetics Reproduction and Development (iGReD), Université Clermont Auvergne, CNRS, Inserm, F-63000 Clermont-Ferrand, France
| | - Amy Hesketh
- Institute of Genetics Reproduction and Development (iGReD), Université Clermont Auvergne, CNRS, Inserm, F-63000 Clermont-Ferrand, France
| | - Marie-Noëlle Pouch-Pélissier
- Institute of Genetics Reproduction and Development (iGReD), Université Clermont Auvergne, CNRS, Inserm, F-63000 Clermont-Ferrand, France
| | - Thierry Pélissier
- Institute of Genetics Reproduction and Development (iGReD), Université Clermont Auvergne, CNRS, Inserm, F-63000 Clermont-Ferrand, France
| | - Ying Huang
- Institute of Plant Sciences Paris-Saclay (IPS2), CNRS, INRAE, Université d’Évry, F-91405 Orsay, France
| | - David Latrasse
- Institute of Plant Sciences Paris-Saclay (IPS2), CNRS, INRAE, Université d’Évry, F-91405 Orsay, France
| | - Moussa Benhamed
- Institute of Plant Sciences Paris-Saclay (IPS2), CNRS, INRAE, Université d’Évry, F-91405 Orsay, France
- Institute of Plant Sciences Paris-Saclay (IPS2), Université de Paris, F-75006 Paris, France
- Institut Universitaire de France (IUF), France
| | - Olivier Mathieu
- Institute of Genetics Reproduction and Development (iGReD), Université Clermont Auvergne, CNRS, Inserm, F-63000 Clermont-Ferrand, France
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2
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Francis NJ, Sihou D. Inheritance of Histone (H3/H4): A Binary Choice? Trends Biochem Sci 2020; 46:5-14. [PMID: 32917507 DOI: 10.1016/j.tibs.2020.08.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Revised: 08/09/2020] [Accepted: 08/14/2020] [Indexed: 02/07/2023]
Abstract
Histones carry information in the form of post-translational modifications (PTMs). For this information to be propagated through cell cycles, parental histones and their PTMs need to be maintained at the same genomic locations. Yet, during DNA replication, every nucleosome in the genome is disrupted to allow passage of the replisome. Recent data have identified histone chaperone activities that are intrinsic components of the replisome and implicate them in maintaining parental histones during DNA replication. We propose that structural and kinetic coordination between DNA replication and replisome-associated histone chaperone activities ensures positional inheritance of histones and their PTMs. When this coordination is perturbed, histones may instead be recycled to random genomic locations by alternative histone chaperones.
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Affiliation(s)
- Nicole J Francis
- Institut de Recherche Clinique de Montréal, 110 Avenue des Pins, Montréal, QC H2W 1R7, Canada; Département de Biochimie et Médecine Moléculaire, Université de Montréal, Montréal, Québec H3C 3J7, Canada; Division of Experimental Medicine, McGill University, 1001 Decarie Boulevard, Montreal, QC H4A 3J1, Canada.
| | - Djamouna Sihou
- Institut de Recherche Clinique de Montréal, 110 Avenue des Pins, Montréal, QC H2W 1R7, Canada; Département de Biochimie et Médecine Moléculaire, Université de Montréal, Montréal, Québec H3C 3J7, Canada
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3
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Rowlands H, Shaban K, Cheng A, Foster B, Yankulov K. Dysfunctional CAF-I reveals its role in cell cycle progression and differential regulation of gene silencing. Cell Cycle 2019; 18:3223-3236. [PMID: 31564230 DOI: 10.1080/15384101.2019.1673100] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Chromatin Assembly Factor I (CAF-I) plays a central role in the reassembly of H3/H4 histones during DNA replication. In S. cerevisiae CAF-I is not essential and its loss is associated with reduced gene silencing at telomeres and increased sensitivity to DNA damage. Two kinases, Cyclin Dependent Kinase (CDK) and Dbf4-Dependent Kinase (DDK), are known to phosphorylate the Cac1p subunit of CAF-I, but their role in the regulation of CAF-I activity is not well understood. In this study we systematically mutated the phosphorylation target sites of these kinases. We show that concomitant mutations of the CDK and DDK target sites of Cac1p lead to growth retardation and significant cell cycle defects, altered cell morphology and increased sensitivity to DNA damage. Surprisingly, some mutations also produced flocculation, a phenotype that is lost in most laboratory strains, and displayed elevated expression of FLO genes. None of these effects is observed upon the destruction of CAF-I. In contrast, the mutations that caused flocculation did not affect gene silencing at the mating type and subtelomeric loci. We conclude that dysfunctional CAF-I produces severe phenotypes, which reveal a possible role of CAF-I in the coordination of DNA replication, chromatin reassembly and cell cycle progression. Our study highlights the role of phosphorylation of Cac1p by CDK and a putative role for DDK in the transmission and re-assembly of chromatin during DNA replication.
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Affiliation(s)
- Hollie Rowlands
- Department of Molecular and Cellular Biology, University of Guelph , Guelph , Canada
| | - Kholoud Shaban
- Department of Molecular and Cellular Biology, University of Guelph , Guelph , Canada
| | - Ashley Cheng
- Department of Molecular and Cellular Biology, University of Guelph , Guelph , Canada
| | - Barret Foster
- Department of Molecular and Cellular Biology, University of Guelph , Guelph , Canada
| | - Krassimir Yankulov
- Department of Molecular and Cellular Biology, University of Guelph , Guelph , Canada
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4
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Chromatin dynamics underlying the precise regeneration of a vertebrate limb - Epigenetic regulation and cellular memory. Semin Cell Dev Biol 2019; 97:16-25. [PMID: 30991117 DOI: 10.1016/j.semcdb.2019.04.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 04/01/2019] [Accepted: 04/09/2019] [Indexed: 12/13/2022]
Abstract
Wound healing, tissue regeneration, and organ regrowth are all regeneration phenomena observed in vertebrates after an injury. However, the ability to regenerate differs greatly among species. Mammals can undergo wound healing and tissue regeneration, but cannot regenerate an organ; for example, they cannot regrow an amputated limb. In contrast, amphibians and fish have much higher capabilities for organ-level regeneration. In addition to medical studies and those in conventional mammalian models such as mice, studies in amphibians and fish have revealed essential factors for and mechanisms of regeneration, including the regrowth of a limb, tail, or fin. However, the molecular nature of the cellular memory needed to precisely generate a new appendage from an amputation site is not fully understood. Recent reports have indicated that organ regeneration is closely related to epigenetic regulation. For example, the methylation status of genomic DNA is related to the expression of regeneration-related genes, and histone-modification enzymes are required to control the chromatin dynamics for regeneration. A proposed mechanism of cellular memory involving an inheritable system of epigenetic modification led us to hypothesize that epigenetic regulation forms the basis for cellular memory in organ regeneration. Here we summarize the current understanding of the role of epigenetic regulation in organ regeneration and discuss the relationship between organ regeneration and epigenetic memory.
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5
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Madamba EV, Berthet EB, Francis NJ. Inheritance of Histones H3 and H4 during DNA Replication In Vitro. Cell Rep 2018; 21:1361-1374. [PMID: 29091772 DOI: 10.1016/j.celrep.2017.10.033] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 09/24/2017] [Accepted: 10/06/2017] [Indexed: 01/08/2023] Open
Abstract
Nucleosomes are believed to carry epigenetic information through the cell cycle, including through DNA replication. It has been known for decades that parental histones are reassembled on newly replicated chromatin, but the mechanisms underlying histone inheritance and dispersal during DNA replication are not fully understood. We monitored the fate of histones H3 or H4 from a single nucleosome through DNA replication in two in vitro systems. In the SV40 system, histones assembled on a single nucleosome positioning sequence can be inherited by their own daughter DNA but are dispersed from their original location. In Xenopus laevis extracts, histones are dynamic, and nucleosomes are repositioned independent of and prior to DNA replication. Nevertheless, a high fraction of histones H3 and H4 that are inherited through DNA replication remains near its starting location. Thus, inheritance of histone proteins and their dispersal can be mechanistically uncoupled.
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Affiliation(s)
- Egbert Vincent Madamba
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
| | - Ellora Bellows Berthet
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
| | - Nicole Jane Francis
- Institut de recherches clinique de Montréal (IRCM) and Département de biochimie et médecine moléculaire, Université de Montréal, Montréal, QC H2W 1R7 Canada.
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6
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Abe T, Kawasumi R, Arakawa H, Hori T, Shirahige K, Losada A, Fukagawa T, Branzei D. Chromatin determinants of the inner-centromere rely on replication factors with functions that impart cohesion. Oncotarget 2018; 7:67934-67947. [PMID: 27636994 PMCID: PMC5356530 DOI: 10.18632/oncotarget.11982] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 09/06/2016] [Indexed: 01/08/2023] Open
Abstract
Replication fork-associated factors promote genome integrity and protect against cancer. Mutations in the DDX11 helicase and the ESCO2 acetyltransferase also cause related developmental disorders classified as cohesinopathies. Here we generated vertebrate model cell lines of these disorders and cohesinopathies-related genes. We found that vertebrate DDX11 and Tim-Tipin are individually needed to compensate for ESCO2 loss in chromosome segregation, with DDX11 also playing complementary roles with ESCO2 in centromeric cohesion. Our study reveals that overt centromeric cohesion loss does not necessarily precede chromosome missegregation, while both these problems correlate with, and possibly originate from, inner-centromere defects involving reduced phosphorylation of histone H3T3 (pH3T3) in the region. Interestingly, the mitotic pH3T3 mark was defective in all analyzed replication-related mutants with functions in cohesion. The results pinpoint mitotic pH3T3 as a postreplicative chromatin mark that is sensitive to replication stress and conducts with different kinetics to robust centromeric cohesion and correct chromosome segregation.
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Affiliation(s)
- Takuya Abe
- IFOM, The FIRC Institute for Molecular Oncology Foundation, Milan, Italy
| | - Ryotaro Kawasumi
- IFOM, The FIRC Institute for Molecular Oncology Foundation, Milan, Italy.,Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa, Hachioji-shi, Tokyo, Japan
| | - Hiroshi Arakawa
- IFOM, The FIRC Institute for Molecular Oncology Foundation, Milan, Italy
| | - Tetsuya Hori
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Katsuhiko Shirahige
- Laboratory of Genome Structure and Function, Research Center for Epigenetic Disease, Institute of Molecular and Cellular Biosciences, University of Tokyo, Yayoi Bunkyo-Ku, Tokyo, Japan
| | - Ana Losada
- Chromosome Dynamics Group, Molecular Oncology Program, Spanish National Cancer Research Centre, Madrid, Spain
| | - Tatsuo Fukagawa
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Dana Branzei
- IFOM, The FIRC Institute for Molecular Oncology Foundation, Milan, Italy
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7
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Li W, Yi J, Agbu P, Zhou Z, Kelley RL, Kallgren S, Jia S, He X. Replication stress affects the fidelity of nucleosome-mediated epigenetic inheritance. PLoS Genet 2017; 13:e1006900. [PMID: 28749973 PMCID: PMC5549764 DOI: 10.1371/journal.pgen.1006900] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 08/08/2017] [Accepted: 06/29/2017] [Indexed: 02/06/2023] Open
Abstract
The fidelity of epigenetic inheritance or, the precision by which epigenetic information is passed along, is an essential parameter for measuring the effectiveness of the process. How the precision of the process is achieved or modulated, however, remains largely elusive. We have performed quantitative measurement of epigenetic fidelity, using position effect variegation (PEV) in Schizosaccharomyces pombe as readout, to explore whether replication perturbation affects nucleosome-mediated epigenetic inheritance. We show that replication stresses, due to either hydroxyurea treatment or various forms of genetic lesions of the replication machinery, reduce the inheritance accuracy of CENP-A/Cnp1 nucleosome positioning within centromere. Mechanistically, we demonstrate that excessive formation of single-stranded DNA, a common molecular abnormality under these conditions, might have correlation with the reduction in fidelity of centromeric chromatin duplication. Furthermore, we show that replication stress broadly changes chromatin structure at various loci in the genome, such as telomere heterochromatin expanding and mating type locus heterochromatin spreading out of the boundaries. Interestingly, the levels of inheritable expanding at sub-telomeric heterochromatin regions are highly variable among independent cell populations. Finally, we show that HU treatment of the multi-cellular organisms C. elegans and D. melanogaster affects epigenetically programmed development and PEV, illustrating the evolutionary conservation of the phenomenon. Replication stress, in addition to its demonstrated role in genetic instability, promotes variable epigenetic instability throughout the epigenome. In this study, we found replication stresses reduce the fidelity of nucleosome-mediated epigenetic inheritance. Using Position Effect Variegation (PEV) in centromere as an indicator of chromatin epigenetic stability, we quantified the precision of nucleosomal inheritance and found replication stresses reduce the fidelity of nucleosome-mediated epigenetic inheritance. Further analysis of genome-wide heterochromatin distribution showed that replication stresses affect chromatin structure by expanding of heterochromatin with locus specificity. Mechanistically, we provide evidence suggesting that excessive formation of single-stranded DNA might have correlation with the reduction in fidelity of centromeric chromatin duplication. Finally, we demonstrated replication stress perturb the development process by reducing the fidelity of chromatin organization duplication in fruit fly and worm, illustrating the broadness and the evolutionary conservation of the phenomenon. Together, our results shed light on the importance of replication stresses cause epigenetic instability in addition to genetic stability.
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Affiliation(s)
- Wenzhu Li
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, China
| | - Jia Yi
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, China
| | - Pamela Agbu
- Department of Biochemistry and Molecular Biology
| | - Zheng Zhou
- Department of Biochemistry and Molecular Biology
| | - Richard L. Kelley
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States of America
| | - Scott Kallgren
- Department of Biological Sciences, Columbia University, New York, NY, United States of America
| | - Songtao Jia
- Department of Biological Sciences, Columbia University, New York, NY, United States of America
| | - Xiangwei He
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, China
- * E-mail:
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8
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Rowlands H, Dhavarasa P, Cheng A, Yankulov K. Forks on the Run: Can the Stalling of DNA Replication Promote Epigenetic Changes? Front Genet 2017; 8:86. [PMID: 28690636 PMCID: PMC5479891 DOI: 10.3389/fgene.2017.00086] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 06/06/2017] [Indexed: 11/13/2022] Open
Abstract
Built of DNA polymerases and multiple associated factors, the replication fork steadily progresses along the DNA template and faithfully replicates DNA. This model can be found in practically every textbook of genetics, with the more complex situation of chromatinized DNA in eukaryotes often viewed as a variation. However, the replication-coupled disassembly/reassembly of chromatin adds significant complexity to the whole replication process. During the course of eukaryotic DNA replication the forks encounter various conditions and numerous impediments. These include nucleosomes with a variety of post-translational modifications, euchromatin and heterochromatin, differentially methylated DNA, tightly bound proteins, active gene promoters and DNA loops. At such positions the forks slow down or even stall. Dedicated factors stabilize the fork and prevent its rotation or collapse, while other factors resolve the replication block and facilitate the resumption of elongation. The fate of histones during replication stalling and resumption is not well understood. In this review we briefly describe recent advances in our understanding of histone turnover during DNA replication and focus on the possible mechanisms of nucleosome disassembly/reassembly at paused replication forks. We propose that replication pausing provides opportunities for an epigenetic change of the associated locus.
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Affiliation(s)
- Hollie Rowlands
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Piriththiv Dhavarasa
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Ashley Cheng
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Krassimir Yankulov
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
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9
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The Effects of Replication Stress on S Phase Histone Management and Epigenetic Memory. J Mol Biol 2017; 429:2011-2029. [DOI: 10.1016/j.jmb.2016.11.011] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 11/10/2016] [Accepted: 11/11/2016] [Indexed: 12/14/2022]
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Iglesias FM, Cerdán PD. Maintaining Epigenetic Inheritance During DNA Replication in Plants. FRONTIERS IN PLANT SCIENCE 2016; 7:38. [PMID: 26870059 PMCID: PMC4735446 DOI: 10.3389/fpls.2016.00038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 01/11/2016] [Indexed: 05/18/2023]
Abstract
Biotic and abiotic stresses alter the pattern of gene expression in plants. Depending on the frequency and duration of stress events, the effects on the transcriptional state of genes are "remembered" temporally or transmitted to daughter cells and, in some instances, even to offspring (transgenerational epigenetic inheritance). This "memory" effect, which can be found even in the absence of the original stress, has an epigenetic basis, through molecular mechanisms that take place at the chromatin and DNA level but do not imply changes in the DNA sequence. Many epigenetic mechanisms have been described and involve covalent modifications on the DNA and histones, such as DNA methylation, histone acetylation and methylation, and RNAi dependent silencing mechanisms. Some of these chromatin modifications need to be stable through cell division in order to be truly epigenetic. During DNA replication, histones are recycled during the formation of the new nucleosomes and this process is tightly regulated. Perturbations to the DNA replication process and/or the recycling of histones lead to epigenetic changes. In this mini-review, we discuss recent evidence aimed at linking DNA replication process to epigenetic inheritance in plants.
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Affiliation(s)
| | - Pablo D. Cerdán
- Fundación Instituto Leloir, IIBBA-CONICET Buenos Aires, Argentina
- Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Buenos Aires, Argentina
- *Correspondence: Pablo D. Cerdán,
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11
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Epigenetic modification maintains intrinsic limb-cell identity in Xenopus limb bud regeneration. Dev Biol 2015; 406:271-82. [PMID: 26282893 DOI: 10.1016/j.ydbio.2015.08.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 08/11/2015] [Accepted: 08/13/2015] [Indexed: 11/21/2022]
Abstract
Many amphibians can regenerate limbs, even in adulthood. If a limb is amputated, the stump generates a blastema that makes a complete, new limb in a process similar to developmental morphogenesis. The blastema is thought to inherit its limb-patterning properties from cells in the stump, and it retains the information despite changes in morphology, gene expression, and differentiation states required by limb regeneration. We hypothesized that these cellular properties are maintained as epigenetic memory through histone modifications. To test this hypothesis, we analyzed genome-wide histone modifications in Xenopus limb bud regeneration. The trimethylation of histone H3 at lysine 4 (H3K4me3) is closely related to an open chromatin structure that allows transcription factors access to genes, whereas the trimethylation of histone H3 at lysine 27 (H3K27me3) is related to a closed chromatin state that blocks the access of transcription factors. We compared these two modification profiles by high-throughput sequencing of samples prepared from the intact limb bud and the regenerative blastema by chromatin immunoprecipitation. For many developmental genes, histone modifications at the transcription start site were the same in the limb bud and the blastema, were stable during regeneration, and corresponded well to limb properties. These results support our hypothesis that histone modifications function as a heritable cellular memory to maintain limb cell properties, despite dynamic changes in gene expression during limb bud regeneration in Xenopus.
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12
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Cea V, Cipolla L, Sabbioneda S. Replication of Structured DNA and its implication in epigenetic stability. Front Genet 2015; 6:209. [PMID: 26136769 PMCID: PMC4468945 DOI: 10.3389/fgene.2015.00209] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 05/29/2015] [Indexed: 11/23/2022] Open
Abstract
DNA replication is an extremely risky process that cells have to endure in order to correctly duplicate and segregate their genome. This task is particularly sensitive to DNA damage and multiple mechanisms have evolved to protect DNA replication as a block to the replication fork could lead to genomic instability and possibly cell death. The DNA in the genome folds, for the most part, into the canonical B-form but in some instances can form complex secondary structures such as G-quadruplexes (G4). These G rich regions are thermodynamically stable and can constitute an obstacle to DNA and RNA metabolism. The human genome contains more than 350,000 sequences potentially capable to form G-quadruplexes and these structures are involved in a variety of cellular processes such as initiation of DNA replication, telomere maintenance and control of gene expression. Only recently, we started to understand how G4 DNA poses a problem to DNA replication and how its successful bypass requires the coordinated activity of ssDNA binding proteins, helicases and specialized DNA polymerases. Their role in the resolution and replication of structured DNA crucially prevents both genetic and epigenetic instability across the genome.
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Affiliation(s)
- Valentina Cea
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche , Pavia, Italy
| | - Lina Cipolla
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche , Pavia, Italy
| | - Simone Sabbioneda
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche , Pavia, Italy
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Abstract
Recent experiments provide fascinating examples of how G4 DNA and G4 RNA structures—aka quadruplexes—may contribute to normal biology and to genomic pathologies. Quadruplexes are transient and therefore difficult to identify directly in living cells, which initially caused skepticism regarding not only their biological relevance but even their existence. There is now compelling evidence for functions of some G4 motifs and the corresponding quadruplexes in essential processes, including initiation of DNA replication, telomere maintenance, regulated recombination in immune evasion and the immune response, control of gene expression, and genetic and epigenetic instability. Recognition and resolution of quadruplex structures is therefore an essential component of genome biology. We propose that G4 motifs and structures that participate in key processes compose the G4 genome, analogous to the transcriptome, proteome, or metabolome. This is a new view of the genome, which sees DNA as not only a simple alphabet but also a more complex geography. The challenge for the future is to systematically identify the G4 motifs that form quadruplexes in living cells and the features that confer on specific G4 motifs the ability to function as structural elements.
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Halley-Stott RP, Gurdon JB. Epigenetic memory in the context of nuclear reprogramming and cancer. Brief Funct Genomics 2013; 12:164-73. [PMID: 23585580 PMCID: PMC3662891 DOI: 10.1093/bfgp/elt011] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Epigenetic memory represents a natural mechanism whereby the identity of a cell is maintained through successive cell cycles, allowing the specification and maintenance of differentiation during development and in adult cells. Cancer is a loss or reversal of the stable differentiated state of adult cells and may be mediated in part by epigenetic changes. The identity of somatic cells can also be reversed experimentally by nuclear reprogramming. Nuclear reprogramming experiments reveal the mechanisms required to activate embryonic gene expression in adult cells and thus provide insight into the reversal of epigenetic memory. In this article, we will introduce epigenetic memory and the mechanisms by which it may operate. We limit our discussion primarily to the context of nuclear reprogramming and briefly discuss the relevance of memory and reprogramming to cancer biology.
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Affiliation(s)
- Richard P Halley-Stott
- The Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QN United Kingdom
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15
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Abstract
The connections between various nuclear processes and specific histone posttranslational modifications are dependent to a large extent on the acquisition of those modifications after histone synthesis. The reestablishment of histone posttranslational modifications after S phase is especially critical for H3K9 and H3K27 trimethylation, both of which are linked with epigenetic memory and must be stably transmitted from one cellular generation to the next. This report uses a proteomic strategy to interrogate how and when the cell coordinates the formation of histone posttranslational modifications during division. Paramount among the findings is that H3K9 and H3K27 trimethylation begins during S phase but is completed only during the subsequent G(1) phase via two distinct pathways from the unmodified and preexisting dimethylated states. In short, we have systematically characterized the temporal origins and methylation pathways for histone posttranslational modifications during the cell cycle.
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