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Hall A, Middlehurst B, Cadogan MAM, Reed X, Billingsley KJ, Bubb VJ, Quinn JP. A SINE-VNTR-Alu at the LRIG2 locus is associated with proximal and distal gene expression in CRISPR and population models. Sci Rep 2024; 14:792. [PMID: 38191889 PMCID: PMC10774264 DOI: 10.1038/s41598-023-50307-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 12/18/2023] [Indexed: 01/10/2024] Open
Abstract
SINE-VNTR-Alu (SVA) retrotransposons represent mobile regulatory elements that have the potential to influence the surrounding genome when they insert into a locus. Evolutionarily recent mobilisation has resulted in loci in the human genome where a given retrotransposon might be observed to be present or absent, termed a retrotransposon insertion polymorphism (RIP). We previously observed that an SVA RIP ~ 2 kb upstream of LRIG2 on chromosome 1, the 'LRIG2 SVA', was associated with differences in local gene expression and methylation, and that the two were correlated. Here, we have used CRISPR-mediated deletion of the LRIG2 SVA in a cell line model to validate that presence of the retrotransposon is directly affecting local expression and provide evidence that is suggestive of a modest role for the SVA in modulating nearby methylation. Additionally, in leveraging an available Hi-C dataset we observed that the LRIG2 SVA was also involved in long-range chromatin interactions with a cluster of genes ~ 300 kb away, and that expression of these genes was to varying degrees associated with dosage of the SVA in both CRISPR cell line and population models. Altogether, these data support a regulatory role for SVAs in the modulation of gene expression, with the latter potentially involving chromatin looping, consistent with the model that RIPs may contribute to interpersonal differences in transcriptional networks.
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Affiliation(s)
- Ashley Hall
- Department of Pharmacology and Therapeutics, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7BE, UK
| | - Ben Middlehurst
- Department of Pharmacology and Therapeutics, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7BE, UK
| | - Max A M Cadogan
- Department of Pharmacology and Therapeutics, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7BE, UK
| | - Xylena Reed
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, 20892, USA
- Center for Alzheimer's and Related Dementias, National Institute on Aging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Kimberley J Billingsley
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, 20892, USA
- Center for Alzheimer's and Related Dementias, National Institute on Aging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Vivien J Bubb
- Department of Pharmacology and Therapeutics, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7BE, UK
| | - John P Quinn
- Department of Pharmacology and Therapeutics, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7BE, UK.
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Chapelle V, Silvestre F. Population Epigenetics: The Extent of DNA Methylation Variation in Wild Animal Populations. EPIGENOMES 2022; 6:31. [PMID: 36278677 PMCID: PMC9589984 DOI: 10.3390/epigenomes6040031] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 09/16/2022] [Accepted: 09/19/2022] [Indexed: 11/17/2022] Open
Abstract
Population epigenetics explores the extent of epigenetic variation and its dynamics in natural populations encountering changing environmental conditions. In contrast to population genetics, the basic concepts of this field are still in their early stages, especially in animal populations. Epigenetic variation may play a crucial role in phenotypic plasticity and local adaptation as it can be affected by the environment, it is likely to have higher spontaneous mutation rate than nucleotide sequences do, and it may be inherited via non-mendelian processes. In this review, we aim to bring together natural animal population epigenetic studies to generate new insights into ecological epigenetics and its evolutionary implications. We first provide an overview of the extent of DNA methylation variation and its autonomy from genetic variation in wild animal population. Second, we discuss DNA methylation dynamics which create observed epigenetic population structures by including basic population genetics processes. Then, we highlight the relevance of DNA methylation variation as an evolutionary mechanism in the extended evolutionary synthesis. Finally, we suggest new research directions by highlighting gaps in the knowledge of the population epigenetics field. As for our results, DNA methylation diversity was found to reveal parameters that can be used to characterize natural animal populations. Some concepts of population genetics dynamics can be applied to explain the observed epigenetic structure in natural animal populations. The set of recent advancements in ecological epigenetics, especially in transgenerational epigenetic inheritance in wild animal population, might reshape the way ecologists generate predictive models of the capacity of organisms to adapt to changing environments.
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Affiliation(s)
- Valentine Chapelle
- Laboratory of Evolutionary and Adaptive Physiology, Institute of Life, Earth, and Environment, University of Namur, 61 Rue de Bruxelles, 5000 Namur, Belgium
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Elmer JL, Hay AD, Kessler NJ, Bertozzi TM, Ainscough EAC, Ferguson-Smith AC. Genomic properties of variably methylated retrotransposons in mouse. Mob DNA 2021; 12:6. [PMID: 33612119 PMCID: PMC7898769 DOI: 10.1186/s13100-021-00235-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 02/02/2021] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Transposable elements (TEs) are enriched in cytosine methylation, preventing their mobility within the genome. We previously identified a genome-wide repertoire of candidate intracisternal A particle (IAP) TEs in mice that exhibit inter-individual variability in this methylation (VM-IAPs) with implications for genome function. RESULTS Here we validate these metastable epialleles and discover a novel class that exhibit tissue specificity (tsVM-IAPs) in addition to those with uniform methylation in all tissues (constitutive- or cVM-IAPs); both types have the potential to regulate genes in cis. Screening for variable methylation at other TEs shows that this phenomenon is largely limited to IAPs, which are amongst the youngest and most active endogenous retroviruses. We identify sequences enriched within cVM-IAPs, but determine that these are not sufficient to confer epigenetic variability. CTCF is enriched at VM-IAPs with binding inversely correlated with DNA methylation. We uncover dynamic physical interactions between cVM-IAPs with low methylation ranges and other genomic loci, suggesting that VM-IAPs have the potential for long-range regulation. CONCLUSION Our findings indicate that a recently evolved interplay between genetic sequence, CTCF binding, and DNA methylation at young TEs can result in inter-individual variability in transcriptional outcomes with implications for phenotypic variation.
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Affiliation(s)
- Jessica L. Elmer
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH UK
| | - Amir D. Hay
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH UK
| | - Noah J. Kessler
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH UK
| | - Tessa M. Bertozzi
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH UK
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A SINE-VNTR- Alu in the LRIG2 Promoter Is Associated with Gene Expression at the Locus. Int J Mol Sci 2020; 21:ijms21228486. [PMID: 33187279 PMCID: PMC7697779 DOI: 10.3390/ijms21228486] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 11/06/2020] [Accepted: 11/09/2020] [Indexed: 12/12/2022] Open
Abstract
The hominid SINE-VNTR-Alu (SVA) retrotransposons represent a repertoire of genomic variation which could have significant effects on genome function. A human-specific SVA in the promoter region of the gene leucine-rich repeats and immunoglobulin-like domains 2 (LRIG2), which we termed SVA_LRIG2, is a common retrotransposon insertion polymorphism (RIP), defined as an element which is polymorphic for its presence or absence in the genome. We hypothesised that this RIP might be associated with differential levels of expression of LRIG2. The RIP genotype of SVA_LRIG2 was determined in a subset of frontal cortex DNA samples from the North American Brain Expression Consortium (NABEC) cohort and was imputed for a larger set of that cohort. Utilising available frontal cortex total RNA-seq and CpG methylation data for this cohort, we observed that increased allele dosage of SVA_LRIG2 was non-significantly associated with a decrease in transcription from the region and significantly associated with increased methylation of the CpG probe nearest to SVA_LRIG2, i.e., SVA_LRIG2 is a significant methylation quantitative trait loci (mQTL) at the LRIG2 locus. These data are consistent with SVA_LRIG2 being a transcriptional regulator, which in part may involve epigenetic modulation.
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Romanov D, Butenko E, Bakhtadze G, Shkurat T. Genome distance between conserved elements in neighborhoods of growth-regulating genes is correlated with morpho-physiological traits in mammals. GENE REPORTS 2019. [DOI: 10.1016/j.genrep.2019.100508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Hou Y, Wang Y, Tang L, Tong X, Wang L, Liu L, Huang S, Zhang J. SAPK10-Mediated Phosphorylation on WRKY72 Releases Its Suppression on Jasmonic Acid Biosynthesis and Bacterial Blight Resistance. iScience 2019; 16:499-510. [PMID: 31229897 PMCID: PMC6593165 DOI: 10.1016/j.isci.2019.06.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 04/19/2019] [Accepted: 06/05/2019] [Indexed: 01/02/2023] Open
Abstract
Bacterial blight caused by the infection of Xanthomonas oryzae pv. oryzae (Xoo) is a devastating disease that severely challenges the yield of rice. Here, we report the identification of a “SAPK10-WRKY72-AOS1” module, through which Xoo infection stimulates the suppression of jasmonic acid (JA) biosynthesis to cause Xoo susceptibility. WRKY72 directly binds to the W-box in the promoter of JA biosynthesis gene AOS1 and represses its transcription by inducing DNA hypermethylation on the target site, which finally led to lower endogenous JA level and higher Xoo susceptibility. Abscisic acid (ABA)-inducible SnRK2-type kinase SAPK10 phosphorylates WRKY72 at Thr 129. The SAPK10-mediated phosphorylation impairs the DNA-binding ability of WRKY72 and releases its suppression on AOS1 and JA biosynthesis. Our work highlights a module of how pathogen stimuli lead to plant susceptibility, as well as a potential pathway for ABA-JA interplay with post-translational modification and epigenetic regulation mechanism involved. WRKY72 negatively regulates rice resistance to Xoo infection and JA synthesis SAPK10 phosphorylates WRKY72 at Thr 129 to impair its DNA binding on AOS1 WRKY72 directly represses AOS1 transcription to attenuate JA synthesis WRKY72 recruits hyper DNA methylation on AOS1 promoter
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Affiliation(s)
- Yuxuan Hou
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Yifeng Wang
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Liqun Tang
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Xiaohong Tong
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Ling Wang
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Lianmeng Liu
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China
| | - Shiwen Huang
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China.
| | - Jian Zhang
- State Key Lab of Rice Biology, China National Rice Research Institute, Hangzhou 311400, China.
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Cardelli M. The epigenetic alterations of endogenous retroelements in aging. Mech Ageing Dev 2018; 174:30-46. [PMID: 29458070 DOI: 10.1016/j.mad.2018.02.002] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Revised: 02/05/2018] [Accepted: 02/08/2018] [Indexed: 02/06/2023]
Abstract
Endogenous retroelements, transposons that mobilize through RNA intermediates, include some of the most abundant repetitive sequences of the human genome, such as Alu and LINE-1 sequences, and human endogenous retroviruses. Recent discoveries demonstrate that these mobile genetic elements not only act as intragenomic parasites, but also exert regulatory roles in living cells. The risk of genomic instability represented by endogenous retroelements is normally counteracted by a series of epigenetic control mechanisms which include, among the most important, CpG DNA methylation. Indeed, most of the genomic CpG sites subjected to DNA methylation in the nuclear DNA are carried by these repetitive elements. As other parts of the genome, endogenous retroelements and other transposable elements are subjected to deep epigenetic alterations during aging, repeatedly observed in the context of organismal and cellular senescence, in human and other species. This review summarizes the current status of knowledge about the epigenetic alterations occurring in this large, non-genic portion of the genome in aging and age-related conditions, with a focus on the causes and the possible functional consequences of these alterations.
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Affiliation(s)
- Maurizio Cardelli
- Advanced Technology Center for Aging Research, Scientific Technological Area, Italian National Research Center on Aging (INRCA), via Birarelli 8, 60121 Ancona, Italy.
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8
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Navarro E, Funtikova AN, Fíto M, Schröder H. Prenatal nutrition and the risk of adult obesity: Long-term effects of nutrition on epigenetic mechanisms regulating gene expression. J Nutr Biochem 2017; 39:1-14. [DOI: 10.1016/j.jnutbio.2016.03.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 03/23/2016] [Accepted: 03/27/2016] [Indexed: 12/19/2022]
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Oh G, Ebrahimi S, Wang SC, Cortese R, Kaminsky ZA, Gottesman II, Burke JR, Plassman BL, Petronis A. Epigenetic assimilation in the aging human brain. Genome Biol 2016; 17:76. [PMID: 27122015 PMCID: PMC4848814 DOI: 10.1186/s13059-016-0946-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2015] [Accepted: 04/11/2016] [Indexed: 12/22/2022] Open
Abstract
Background Epigenetic drift progressively increases variation in DNA modification profiles of aging cells, but the finale of such divergence remains elusive. In this study, we explored the dynamics of DNA modification and transcription in the later stages of human life. Results We find that brain tissues of older individuals (>75 years) become more similar to each other, both epigenetically and transcriptionally, compared with younger individuals. Inter-individual epigenetic assimilation is concurrent with increasing similarity between the cerebral cortex and the cerebellum, which points to potential brain cell dedifferentiation. DNA modification analysis of twins affected with Alzheimer’s disease reveals a potential for accelerated epigenetic assimilation in neurodegenerative disease. We also observe loss of boundaries and merging of neighboring DNA modification and transcriptomic domains over time. Conclusions Age-dependent epigenetic divergence, paradoxically, changes to convergence in the later stages of life. The newly described phenomena of epigenetic assimilation and tissue dedifferentiation may help us better understand the molecular mechanisms of aging and the origins of diseases for which age is a risk factor. Electronic supplementary material The online version of this article (doi:10.1186/s13059-016-0946-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gabriel Oh
- Krembil Family Epigenetics Laboratory, Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, 250 College St. R130, Toronto, Ontario, M5T 1R8, Canada
| | - Sasha Ebrahimi
- Krembil Family Epigenetics Laboratory, Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, 250 College St. R130, Toronto, Ontario, M5T 1R8, Canada
| | - Sun-Chong Wang
- Institute of Systems Biology and Bioinformatics, National Central University, Chungli, 320, Taiwan
| | - Rene Cortese
- Krembil Family Epigenetics Laboratory, Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, 250 College St. R130, Toronto, Ontario, M5T 1R8, Canada.,Department of Pediatrics, University of Chicago, Chicago, Illinois, 60637, USA
| | - Zachary A Kaminsky
- Department of Psychiatry and Behavioral Sciences, School of Medicine, Johns Hopkins University, Baltimore, Maryland, 21287, USA
| | - Irving I Gottesman
- Departments of Psychology and Psychiatry, University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - James R Burke
- Duke University Medical Center, Duke University, Box 2900, Durham, North Carolina, 27701, USA
| | - Brenda L Plassman
- Duke University Medical Center, Duke University, Box 41, Durham, North Carolina, 27701, USA
| | - Art Petronis
- Krembil Family Epigenetics Laboratory, Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, 250 College St. R130, Toronto, Ontario, M5T 1R8, Canada.
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Abstract
The term epigenetics refers to stable patterns of gene expression that are seen during differentiation or X chromosome inactivation and are not dependent on dynamic changes in coding DNA. These gene expression states are encoded in the epigenome - a collection of marks on DNA or on histone tails that are established during embryogenesis. Genome-wide studies in aging cells and tissues have uncovered stochastic DNA methylation drift (gradual increases or decreases at specific loci) that reflects imperfect maintenance of epigenetic marks. Drift creates epigenetic mosaicism in aging stem cells that could potentially restrict their plasticity and worsen phenotypes such as stem cell exhaustion and focal proliferative defects that can lead to cancer.
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Estécio MRH, Gallegos J, Dekmezian M, Lu Y, Liang S, Issa JPJ. SINE retrotransposons cause epigenetic reprogramming of adjacent gene promoters. Mol Cancer Res 2012; 10:1332-42. [PMID: 22952045 DOI: 10.1158/1541-7786.mcr-12-0351] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Almost half of the human genome and as much as 40% of the mouse genome is composed of repetitive DNA sequences. The majority of these repeats are retrotransposons of the SINE and LINE families, and such repeats are generally repressed by epigenetic mechanisms. It has been proposed that these elements can act as methylation centers from which DNA methylation spreads into gene promoters in cancer. Contradictory to a methylation center function, we have found that retrotransposons are enriched near promoter CpG islands that stay methylation-free in cancer. Clearly, it is important to determine which influence, if any, these repetitive elements have on nearby gene promoters. Using an in vitro system, we confirm here that SINE B1 elements can influence the activity of downstream gene promoters, with acquisition of DNA methylation and loss of activating histone marks, thus resulting in a repressed state. SINE sequences themselves did not immediately acquire DNA methylation but were marked by H3K9me2 and H3K27me3. Moreover, our bisulfite sequencing data did not support that gain of DNA methylation in gene promoters occurred by methylation spreading from SINE B1 repeats. Genome-wide analysis of SINE repeats distribution showed that their enrichment is directly correlated with the presence of USF1, USF2, and CTCF binding, proteins with insulator function. In summary, our work supports the concept that SINE repeats interfere negatively with gene expression and that their presence near gene promoters is counter-selected, except when the promoter is protected by an insulator element.
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Affiliation(s)
- Marcos R H Estécio
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Baylor College of Medicine, Houston, Texas 77030, USA.
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Zhang Y, Shu J, Si J, Shen L, Estecio MRH, Issa JPJ. Repetitive elements and enforced transcriptional repression co-operate to enhance DNA methylation spreading into a promoter CpG-island. Nucleic Acids Res 2012; 40:7257-68. [PMID: 22600741 PMCID: PMC3424568 DOI: 10.1093/nar/gks429] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Repression of many tumor suppressor genes in cancer is concurrent with aberrantly increased DNA methylation levels at promoter CpG islands (CGIs). About one-fourth of empirically defined human promoters are surrounded by or contain clustered repetitive elements. It was previously observed that a sharp transition of methylation exists between highly methylated repetitive elements and unmethylated promoter-CGIs in normal tissues. The factors that lead to aberrant CGI hypermethylation in cancer remain poorly understood. Here, we established a site-specific integration system with enforced local transcriptional repression in colorectal cancer cells and monitored the occurrence of initial de novo methylation at specific CG sites adjacent to the CGI of the INSL6 promoter, which could be accelerated by binding a KRAB-containing transcriptional factor. Additional repetitive elements from P16 and RIL (PDLIM4), if situated adjacent to the promoter of INSL6, could confer DNA methylation spreading into the CGI particularly in the setting of KRAB-factor binding. However, a repressive chromatin alone was not sufficient to initiate DNA methylation, which required specific DNA sequences and was integration-site (and/or cell-line) specific. Overall, these results demonstrate a requirement for specific DNA sequences to trigger de novo DNA methylation, and repetitive elements as cis-regulatory factors to cooperate with advanced transcriptional repression in promoting methylation spreading.
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Affiliation(s)
- Yan Zhang
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA
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Promotion of variant human mammary epithelial cell outgrowth by ionizing radiation: an agent-based model supported by in vitro studies. Breast Cancer Res 2010; 12:R11. [PMID: 20146798 PMCID: PMC2880432 DOI: 10.1186/bcr2477] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Revised: 01/20/2010] [Accepted: 02/10/2010] [Indexed: 01/25/2023] Open
Abstract
Introduction Most human mammary epithelial cells (HMEC) cultured from histologically normal breast tissues enter a senescent state termed stasis after 5 to 20 population doublings. These senescent cells display increased size, contain senescence associated β-galactosidase activity, and express cyclin-dependent kinase inhibitor, p16INK4A (CDKN2A; p16). However, HMEC grown in a serum-free medium, spontaneously yield, at low frequency, variant (v) HMEC that are capable of long-term growth and are susceptible to genomic instability. We investigated whether ionizing radiation, which increases breast cancer risk in women, affects the rate of vHMEC outgrowth. Methods Pre-stasis HMEC cultures were exposed to 5 to 200 cGy of sparsely (X- or γ-rays) or densely (1 GeV/amu 56Fe) ionizing radiation. Proliferation (bromodeoxyuridine incorporation), senescence (senescence-associated β-galactosidase activity), and p16 expression were assayed in subcultured irradiated or unirradiated populations four to six weeks following radiation exposure, when patches of vHMEC became apparent. Long-term growth potential and p16 promoter methylation in subsequent passages were also monitored. Agent-based modeling, incorporating a simple set of rules and underlying assumptions, was used to simulate vHMEC outgrowth and evaluate mechanistic hypotheses. Results Cultures derived from irradiated cells contained significantly more vHMEC, lacking senescence associated β-galactosidase or p16 expression, than cultures derived from unirradiated cells. As expected, post-stasis vHMEC cultures derived from both unirradiated and irradiated cells exhibited more extensive methylation of the p16 gene than pre-stasis HMEC cultures. However, the extent of methylation of individual CpG sites in vHMEC samples did not correlate with passage number or treatment. Exposure to sparsely or densely ionizing radiation elicited similar increases in the numbers of vHMEC compared to unirradiated controls. Agent-based modeling indicated that radiation-induced premature senescence of normal HMEC most likely accelerated vHMEC outgrowth through alleviation of spatial constraints. Subsequent experiments using defined co-cultures of vHMEC and senescent cells supported this mechanism. Conclusions Our studies indicate that ionizing radiation can promote the outgrowth of epigenetically altered cells with pre-malignant potential.
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Oyer JA, Chu A, Brar S, Turker MS. Aberrant epigenetic silencing is triggered by a transient reduction in gene expression. PLoS One 2009; 4:e4832. [PMID: 19279688 PMCID: PMC2654015 DOI: 10.1371/journal.pone.0004832] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2009] [Accepted: 02/17/2009] [Indexed: 12/31/2022] Open
Abstract
Background Aberrant epigenetic silencing plays a major role in cancer formation by inactivating tumor suppressor genes. While the endpoints of aberrant silencing are known, i.e., promoter region DNA methylation and altered histone modifications, the triggers of silencing are not known. We used the tet-off system to test the hypothesis that a transient reduction in gene expression will sensitize a promoter to undergo epigenetic silencing. Methodology/Principal Findings The tet responsive promoter (PTRE) was used to drive expression of the selectable human HPRT cDNA in independent transfectants of an Hprt deficient mouse cell line. In this system, high basal HPRT expression is greatly reduced when doxycycline (Dox) is added to the culture medium. Exposure of the PTRE-HPRT transfectants to Dox induced HPRT deficient clones in a time dependent manner. A molecular analysis demonstrated promoter region DNA methylation, loss of histone modifications associated with expression (i.e., H3 lysine 9 and 14 acetylation and lysine 4 methylation), and acquisition of the repressive histone modification H3 lysine 9 methylation. These changes, which are consistent with aberrant epigenetic silencing, were not present in the Dox-treated cultures, with the exception of reduced H3 lysine 14 acetylation. Silenced alleles readily reactivated spontaneously or after treatment of cells with inhibitors of histone deacetylation and/or DNA methylation, but re-silencing of reactivated alleles did not require a new round of Dox exposure. Inhibition of histone deacetylation inhibited both the induction of silencing and re-silencing, whereas inhibition of DNA methylation had no such effect. Conclusions/Significance This study demonstrates that a transient reduction in gene expression triggers a pathway for aberrant silencing in mammalian cells and identifies histone deacetylation as a critical early step in this process. DNA methylation, in contrast, is a secondary step in the silencing pathway under study. A model to explain these observations is offered.
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Affiliation(s)
- Jon A. Oyer
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Adrian Chu
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, Oregon, United States of America,
| | - Sukhmani Brar
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, Oregon, United States of America,
| | - Mitchell S. Turker
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, Oregon, United States of America
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, Oregon, United States of America,
- * E-mail:
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15
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Abstract
At certain evolutionary junctures, two or more mutations participating in the build-up of a new complex function may be required to become available simultaneously in the same individuals. How could this happen in higher organisms whose populations are small compared to those of microbes, and in which chances of combined nearly simultaneous highly specific favorable mutations are correspondingly low? The question can in principle be answered for regulatory evolution, one of the basic processes of evolutionary change. A combined resetting of transcription rates in several genes could occur in the same individual. It is proposed that, in eukaryotes, changes in epigenetic trends and epigenetically transforming encounters between alternative chromatin structures could arise frequently enough so as to render probable particular conjunctions of changed transcription rates. Such conjunctions could involve mutational changes with low specificity requirements in gene-associated regions of non-protein-coding sequences. The effects of such mutations, notably when they determine the use of histone variants and covalent modifications of histones, can be among those that migrate along chromatin. Changes in chromatin structure are often cellularly inheritable over at least a limited number of generations of cells, and of individuals when the germ line is involved. SINEs and LINEs, which have been considered "junk DNA", are among the repeat sequences that would appear liable to have teleregulatory effects on the function of a nearby promoter, through changes in their numbers and distribution. There may also be present preexisting unstably inheritable epigenetic trends leading to cellular variegation, trends endemic in a cell population based on DNA sequences previously established in the neighborhood. Either way, epigenetically conditioned teleregulatory trends may display only limited penetrance. The imposition at a distance of new chromatin structures with regulatory impact can occur in cis as well as in trans, and is examined as intrachromosomally spreading teleregulation and interchromosomal "gene kissing". The chances for two or more particular epigenetically determined regulatory trends to occur together in a cell are increased thanks to the proposed low specificity requirements for most of the pertinent sequence changes in intergenic and intronic DNA or in the distribution of middle repetitive sequences that have teleregulatory impact. Inheritable epigenetic changes ("epimutations") with effects at a distance would then perdure over the number of generations required for "assimilation" of the several regulatory novelties through the occurrence and selection, gene by gene, of specific classical mutations. These mutations would have effects similar to the epigenetic effects, yet would provide stability and penetrance. The described epigenetic/genetic partnership may well at times have opened the way toward certain complex new functions. Thus, the presence of "junk DNA", through co-determining the (higher or lower) order and the variants of chromatin structure with regulatory effects at a distance, might make an important contribution to the evolution of complex organisms.
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Affiliation(s)
- Emile Zuckerkandl
- Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
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16
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Abstract
Development of methods that will allow exogenous imposition of inheritable gene-specific methylation patterns has potential application in both therapeutics and in basic research. An ongoing approach is the use of targeted DNA methyltransferases, which consist of a fusion between gene-targeted zinc-finger proteins and prokaryotic DNA cytosine methyltransferases. These enzymes however have so far demonstrated significant and unacceptable levels of non-targeted methylation. We now report the development of second-generation targeted methyltransferase enzymes comprising enhanced zinc-finger arrays coupled to methyltransferase mutants that are functionally dominated by their zinc-finger component. Both in vitro plasmid methylation studies and a novel bacterial assay reveal a high degree of target-specific methylation by these enzymes. Furthermore, we demonstrate for the first time transient expression of targeted cytosine methyltransferase in mammalian cells resulting in the specific methylation of a chromosomal locus. Importantly, the resultant methylation pattern is inherited through successive cell divisions.
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Affiliation(s)
| | - Kevin G. Ford
- To whom correspondence should be addressed. Tel: +44 207 848 5909; Fax: +44 207 733 3877;
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17
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Abstract
One of the oldest unsolved problems in genetics is the observation that gene silencing can 'spread' along a chromosome. Although spreading has been widely perceived as a process of long-range assembly of heterochromatin proteins, such 'oozing' might not apply in most cases. Rather, long-range silencing seems to be a dynamic process, involving local diffusion of histone-modifying enzymes from source binding sites to low-affinity sites nearby. Discontinuous silencing might reflect looping interactions, whereas the spreading of continuous silencing might be driven by the processive movement of RNA or DNA polymerases. We review the evidence for the spreading of silencing in many contexts and organisms and conclude that multiple mechanisms have evolved that silence genes at a distance.
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Affiliation(s)
- Paul B Talbert
- Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109, USA
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18
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Sontag LB, Lorincz MC, Georg Luebeck E. Dynamics, stability and inheritance of somatic DNA methylation imprints. J Theor Biol 2006; 242:890-9. [PMID: 16806276 DOI: 10.1016/j.jtbi.2006.05.012] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Revised: 04/07/2006] [Accepted: 05/05/2006] [Indexed: 12/31/2022]
Abstract
Recent research highlights the role of CpG methylation in genomic imprinting, histone and chromatin modification, transcriptional regulation, and 'gene silencing' in cancer development. An unresolved issue, however, is the role of stable inheritance of factors that manage epigenetic imprints in renewing or expanding cell populations in soma. Here we propose a mathematical model of CpG methylation that is consistent with the cooperative roles of de novo and maintenance methylation. This model describes (1) the evolution of methylation imprints toward stable, yet noisy equilibria, (2) bifurcations in methylation levels, thus the dual stability of both hypo- and hypermethylated genomic regions, and (3) sporadic transitions from hypo- to hypermethylated equilibria as a result of methylation noise in a finite system of CpG sites. Our model not only affords an explanation of the persistent coexistence of these two equilibria, but also of sporadic changes of site-specific methylation levels that may alter preset epigenetic imprints in a renewing cell population.
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Affiliation(s)
- Laura B Sontag
- Computational and Systems Biology Program, Massachusetts Institute of Technology, Room 68-371, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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19
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Shimizu M, Yoshimoto T, Sato M, Matsuzawa A, Takeda Y. Frequency and resistance of CD95 (Fas/Apo-1) gene-transfected tumor cells to CD95-mediated apoptosis by the elimination and methylation of integrated DNA. Int J Cancer 2006; 119:585-92. [PMID: 16506211 DOI: 10.1002/ijc.21873] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
It is important for more effective gene therapies to clarify the mechanisms by which cDNA integrated into cells can maintain or lose its function in vivo. We evaluated genetic and epigenetic events leading to alternation of the introduced CD95 (Fas/Apo-1) gene as a model of gene therapy. Solid tumors formed by CD95 cDNA-transfected hepatoma cells (F6b) were almost completely cured by a single treatment of anti-CD95 monoclonal antibody (mAb) but recurred in gld/gld lpr/lpr mice after initial complete response. Recurred tumors were resistant to repeated mAb treatment. The ratio of resistant cells in tumors was estimated as 4.2 cells per 10(6) cells. The CD95-resistant tumor contained CD95-vanished and CD95-decreased cells. CD95-vanished cells were due to the deletion of CD95cDNA. However, CD95-decreased cells retained CD95cDNA, which was highly methylated when determined with methylation-dependent enzymes and a demethylation reagent, indicating that DNA methylation was responsible for the reduced CD95 expression and resistance to mAb. CD95-decreased cells reduced the CD95 expression further but did not delete cDNA after a second in vivo treatment with anti-CD95 mAb, suggesting that the elimination of cDNA is not induced after its methylation and that cells containing methylated genes became more resistant by further methylation. Thus, the elimination and methylation of integrated cDNA appear to occur through different mechanisms. Our study of resistant tumor cells, which arose by both mutational and epigenetic modifications of the introduced CD95 plasmid, provides important and fundamental information about the fate of introduced cDNA, augmenting the efficiency of gene therapy.
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MESH Headings
- Animals
- Antibodies, Monoclonal/pharmacology
- Apoptosis/drug effects
- Apoptosis/genetics
- Cell Line, Tumor
- Cell Survival/drug effects
- Cell Survival/genetics
- DNA Methylation
- DNA, Complementary/genetics
- DNA, Complementary/metabolism
- Deoxyribonuclease HpaII/metabolism
- Dose-Response Relationship, Drug
- Drug Resistance, Neoplasm/genetics
- Gene Expression Regulation, Neoplastic
- Gene Frequency
- Liver Neoplasms, Experimental/drug therapy
- Liver Neoplasms, Experimental/genetics
- Liver Neoplasms, Experimental/pathology
- Mice
- Mice, Inbred C3H
- Nuclear Proteins/genetics
- Nuclear Receptor Co-Repressor 1
- Repressor Proteins/genetics
- Transfection
- fas Receptor/genetics
- fas Receptor/immunology
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Affiliation(s)
- Motomu Shimizu
- Medical R&D Center, Tokyo Metropolitan Institute of Medical Science, Tokyo Metropolitan Organization for Medical Research, Tokyo, 113-8613 Japan.
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20
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Vinogradov AE. Dualism of gene GC content and CpG pattern in regard to expression in the human genome: magnitude versus breadth. Trends Genet 2005; 21:639-43. [PMID: 16202472 DOI: 10.1016/j.tig.2005.09.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Revised: 08/10/2005] [Accepted: 09/09/2005] [Indexed: 11/26/2022]
Abstract
In this article, I show that, in the human genome, the GC content in genes (but not the CpG island in the promoter) is related to the maximum level of gene expression among tissues, whereas the promoter CpG island and gene CpG level are more strongly related to the breadth of expression among tissues. The relevance of gene GC content to expression cannot be a consequence (i.e. a byproduct) of transcription because it does not correlate with expression in the germline. The variation of GC content and CpG level can determine the characteristics of gene expression in a synergistic interplay with transcription-factor-binding sites (mediated by chromatin condensation).
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21
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Abstract
DNA methylation is the epigenetic modification, which introduces 5mC as fifth base onto DNA. As for the distribution of 5mCs, it is well known that they distribute themselves in a non-random fashion in genomic DNA so that methylation pattern is characterized by the presence of methylated cytosines on the bulk of DNA while the unmethylated ones are mainly located within particular regions termed CpG islands. These regions represent about 1% of genomic DNA and are generally found in the promoter region of housekeeping genes. Their unmethylated state, which is an essential condition for the correct expression of correlated genes, is paradoxical if one considers that these regions are termed CpG islands because they are particularly rich in this dinucleotide, which is the best substrate for enzymes involved in DNA methylation. Anomalous insertion of methyl groups in these regions generally leads to the lack of transcription of correlated genes. An interesting scientific problem is to clarify the mechanism(s) whereby CpG islands, which remain protected from methylation in normal cells, are susceptible to methylation in tumor cells. How the CpG moieties in CpG islands become vulnerable or resistant to the action of DNA methyltransferases and can thus lose or maintain their characteristic pattern of methylation is still an open question. Our aim is to gather some mechanisms regarding this intriguing enigma, which, despite all energy spent, still remains an unresolved puzzle.
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Affiliation(s)
- Paola Caiafa
- Department of Cellular Biotechnology and Hematology, University of Rome La Sapienza, 00161 Rome, Italy.
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22
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Ronai D, Berru M, Shulman MJ. The epigenetic stability of the locus control region-deficient IgH locus in mouse hybridoma cells is a clonally varying, heritable feature. Genetics 2005; 167:411-21. [PMID: 15166165 PMCID: PMC1470874 DOI: 10.1534/genetics.167.1.411] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Cis-acting elements such as enhancers and locus control regions (LCRs) prevent silencing of gene expression. We have shown previously that targeted deletion of an LCR in the immunoglobulin heavy-chain (IgH) locus creates conditions in which the immunoglobulin micro heavy chain gene can exist in either of two epigenetically inherited states, one in which micro expression is positive and one in which micro expression is negative, and that the positive and negative states are maintained by a cis-acting mechanism. As described here, the stability of these states, i.e., the propensity of a cell to switch from one state to the other, varied among subclones and was an inherited, clonal feature. A similar variation in stability was seen for IgH loci that both lacked and retained the matrix attachment regions associated with the LCR. Our analysis of cell hybrids formed by fusing cells in which the micro expression had different stabilities indicated that stability was also determined by a cis-acting feature of the IgH locus. Our results thus show that a single-copy gene in the same chromosomal location and in the presence of the same transcription factors can exist in many different states of expression.
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Affiliation(s)
- Diana Ronai
- Immunology Department, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
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23
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Niculescu MD, Craciunescu CN, Zeisel SH. Gene expression profiling of choline-deprived neural precursor cells isolated from mouse brain. ACTA ACUST UNITED AC 2004; 134:309-22. [PMID: 15836926 DOI: 10.1016/j.molbrainres.2004.11.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Revised: 11/01/2004] [Accepted: 11/04/2004] [Indexed: 12/16/2022]
Abstract
Choline is an essential nutrient and an important methyl donor. Choline deficiency alters fetal development of the hippocampus in rodents and these changes are associated with decreased memory function lasting throughout life. Also, choline deficiency alters global and gene-specific DNA methylation in several models. This gene expression profiling study describes changes in cortical neural precursor cells from embryonic day 14 mice, after 48 h of exposure to a choline-deficient medium. Using Significance Analysis of Microarrays, we found the expression of 1003 genes to be significantly changed (from a total of 16,000 total genes spotted on the array), with a false discovery rate below 5%. A total of 846 genes were overexpressed while 157 were underexpressed. Classification by gene ontology revealed that 331 of these genes modulate cell proliferation, apoptosis, neuronal and glial differentiation, methyl metabolism, and calcium-binding protein classes. Twenty-seven genes that had changed expression have previously been reported to be regulated by promoter or intron methylation. These findings support our previous work suggesting that choline deficiency decreases the proliferation of neural precursors and possibly increases premature neuronal differentiation and apoptosis.
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Affiliation(s)
- Mihai D Niculescu
- Department of Nutrition, School of Public Health and School of Medicine, University of North Carolina at Chapel Hill, 2212 McGavran-Greenberg Hall, Chapel Hill, NC 27599-7461, USA
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