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Elango R, Nilavar NM, Li AG, Nguyen D, Rass E, Duffey EE, Jiang Y, Abakir A, Willis NA, Houseley J, Scully R. Two-ended recombination at a Flp-nickase-broken replication fork. Mol Cell 2024:S1097-2765(24)00911-0. [PMID: 39631396 DOI: 10.1016/j.molcel.2024.11.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2024] [Revised: 09/23/2024] [Accepted: 11/07/2024] [Indexed: 12/07/2024]
Abstract
Replication fork collision with a DNA nick can generate a one-ended break, fostering genomic instability. The opposing fork's collision with the nick could form a second DNA end, enabling conservative repair by homologous recombination (HR). To study mechanisms of nickase-induced HR, we developed the Flp recombinase "step arrest" nickase in mammalian cells. A Flp-nick induces two-ended, BRCA2/RAD51-dependent short tract gene conversion (STGC), BRCA2/RAD51-independent long tract gene conversion, and discoordinated two-ended invasions. HR pathways induced by a replication-independent break and the Flp-nickase differ in their dependence on BRCA1, MRE11, and CtIP. To determine the origin of the second DNA end during Flp-nickase-induced STGC, we blocked the opposing fork using a Tus/Ter replication fork barrier (RFB). Flp-nickase-induced STGC remained robust and two ended. Thus, a single replication fork's collision with a Flp-nick triggers two-ended HR, possibly reflecting replicative bypass of lagging strand nicks. This response may limit genomic instability during replication of nicked DNA.
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Abakir A, Ruzov A. A model for a dual function of N 6-methyladenosine in R-loop regulation. Nat Genet 2024; 56:1995-1998. [PMID: 39289548 DOI: 10.1038/s41588-024-01905-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/19/2024]
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3
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Shah P, Hill R, Dion C, Clark SJ, Abakir A, Willems J, Arends MJ, Garaycoechea JI, Leitch HG, Reik W, Crossan GP. Primordial germ cell DNA demethylation and development require DNA translesion synthesis. Nat Commun 2024; 15:3734. [PMID: 38702312 PMCID: PMC11068800 DOI: 10.1038/s41467-024-47219-2] [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: 06/21/2023] [Accepted: 03/25/2024] [Indexed: 05/06/2024] Open
Abstract
Mutations in DNA damage response (DDR) factors are associated with human infertility, which affects up to 15% of the population. The DDR is required during germ cell development and meiosis. One pathway implicated in human fertility is DNA translesion synthesis (TLS), which allows replication impediments to be bypassed. We find that TLS is essential for pre-meiotic germ cell development in the embryo. Loss of the central TLS component, REV1, significantly inhibits the induction of human PGC-like cells (hPGCLCs). This is recapitulated in mice, where deficiencies in TLS initiation (Rev1-/- or PcnaK164R/K164R) or extension (Rev7 -/-) result in a > 150-fold reduction in the number of primordial germ cells (PGCs) and complete sterility. In contrast, the absence of TLS does not impact the growth, function, or homeostasis of somatic tissues. Surprisingly, we find a complete failure in both activation of the germ cell transcriptional program and in DNA demethylation, a critical step in germline epigenetic reprogramming. Our findings show that for normal fertility, DNA repair is required not only for meiotic recombination but for progression through the earliest stages of germ cell development in mammals.
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Elango R, Nilavar N, Li AG, Duffey EE, Jiang Y, Nguyen D, Abakir A, Willis NA, Houseley J, Scully R. Two-ended recombination at a Flp-nickase-broken replication fork. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.10.588130. [PMID: 38645103 PMCID: PMC11030319 DOI: 10.1101/2024.04.10.588130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Collision of a replication fork with a DNA nick is thought to generate a one-ended break, fostering genomic instability. Collision of the opposing converging fork with the nick could, in principle, form a second DNA end, enabling conservative repair by homologous recombination (HR). To study mechanisms of nickase-induced HR, we developed the Flp recombinase "step arrest" nickase in mammalian cells. Flp-nickase-induced HR entails two-ended, BRCA2/RAD51-dependent short tract gene conversion (STGC), BRCA2/RAD51-independent long tract gene conversion, and discoordinated two-ended invasions. HR induced by a replication-independent break and by the Flp-nickase differ in their dependence on BRCA1 . To determine the origin of the second DNA end during Flp-nickase-induced STGC, we blocked the opposing fork using a site-specific Tus/ Ter replication fork barrier. Flp-nickase-induced STGC remained robust and two-ended. Thus, collision of a single replication fork with a Flp-nick can trigger two-ended HR, possibly reflecting replicative bypass of lagging strand nicks. This response may limit genomic instability during replication of a nicked DNA template.
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Shah P, Hill R, Clark S, Dion C, Abakir A, Arends M, Leitch H, Reik W, Crossan G. Primordial germ cell DNA demethylation and development require DNA translesion synthesis.. [DOI: 10.1101/2023.07.05.547775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2024]
Abstract
AbstractMutations in DNA damage response (DDR) factors are associated with human infertility, which affects up to 15% of the population. It remains unclear if the role of DDR is solely in meiosis. One pathway implicated in human fertility is DNA translesion synthesis (TLS), which allows replication impediments to be bypassed. We find that TLS is essential for pre-meiotic germ cell development in the embryo. Loss of the central TLS component, REV1, significantly inhibits the induction of human PGC-like cells (hPGCLCs). This is recapitulated in mice, where deficiencies in TLS initiation (Rev1-/-orPcnaK164R/K164R) or extension (Rev7-/-) result in a >150-fold reduction in the number of primordial germ cells (PGCs) and complete sterility. In contrast, the absence of TLS does not impact the growth, function, or homeostasis of somatic tissues. Surprisingly, we find a complete failure in both activation of the germ cell transcriptional program and in DNA demethylation, a critical step in germline epigenetic reprogramming. Our findings show that for normal fertility, DNA repair is required not only for meiotic recombination but for progression through the earliest stages of germ cell development in mammals.
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Vijg J, Schumacher B, Abakir A, Antonov M, Bradley C, Cagan A, Church G, Gladyshev VN, Gorbunova V, Maslov AY, Reik W, Sharifi S, Suh Y, Walsh K. Mitigating age-related somatic mutation burden. Trends Mol Med 2023; 29:530-540. [PMID: 37121869 DOI: 10.1016/j.molmed.2023.04.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 04/05/2023] [Accepted: 04/06/2023] [Indexed: 05/02/2023]
Abstract
Genomes are inherently unstable and require constant DNA repair to maintain their genetic information. However, selective pressure has optimized repair mechanisms in somatic cells only to allow transmitting genetic information to the next generation, not to maximize sequence integrity long beyond the reproductive age. Recent studies have confirmed that somatic mutations, due to errors during genome repair and replication, accumulate in tissues and organs of humans and model organisms. Here, we describe recent advances in the quantitative analysis of somatic mutations in vivo. We also review evidence for or against a possible causal role of somatic mutations in aging. Finally, we discuss options to prevent, delay or eliminate de novo, random somatic mutations as a cause of aging.
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Abakir A, Reik W. Direct methylation sequencing. Nat Chem Biol 2023:10.1038/s41589-023-01356-9. [PMID: 37322154 DOI: 10.1038/s41589-023-01356-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
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Starczak M, Abakir A, Ruzov A, Gackowski D. Detection and Quantification of RNA Modifications on RNA-DNA Hybrids Using SID-UPLC-MS/MS. Methods Mol Biol 2022; 2528:127-143. [PMID: 35704189 DOI: 10.1007/978-1-0716-2477-7_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
R-loops are three-stranded nucleic acid structures consisting of an RNA-DNA hybrid and an unpaired strand of nontemplate DNA that represent a major source of genomic instability and are involved in regulation of several important biological processes in eukaryotic cells. A growing body of experimental evidence suggests that RNA moieties of RNA-DNA hybrids may convey RNA modifications influencing various aspects of R-loop biology. Here we present a protocol for quantitative analysis of RNA modifications on RNA-DNA hybrids using stable-isotope dilution ultraperformance liquid chromatography coupled with tandem mass spectrometry (SID-UPLC-MS/MS). Supplemented by other techniques, this method can be instrumental in deciphering the roles of RNA modifications in R-loop metabolism.
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Abakir A, Alenezi F, Ruzov A. Detecting and Mapping N6-Methyladenosine on RNA/DNA Hybrids. Methods Mol Biol 2022; 2528:329-344. [PMID: 35704202 DOI: 10.1007/978-1-0716-2477-7_22] [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] [Indexed: 06/15/2023]
Abstract
N6-methyladenosine (m6A) is an RNA modification essential for posttranscriptional regulation of gene expression in eukaryotes. We recently demonstrated that m6A decorates the RNA components of R-loops, specific nucleic acid structures consisting of an RNA/DNA hybrid and a single strand of non-template DNA, that represent a major source of genetic instability and, at the same time, contribute to regulation of gene expression in mammalian cells. According to growing body of experimental evidence, adenosine methylation affects stability of these structures and potentially influences various aspects of their metabolism. Here, we present two methods for detection and analysis of m6A-containing RNA/DNA hybrids: an immunostaining protocol allowing investigation of their spatial distribution in eukaryotic cells and m6A-DNA immunoprecipitation (DIP), an antibody-based technique that permits their genome mapping and locus-specific analysis. In addition to the m6A-focused studies, these methodologies can also contribute to elucidating the functional roles of other RNA modifications in R-loop biology.
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Blythe MJ, Kocer A, Rubio-Roldan A, Giles T, Abakir A, Ialy-Radio C, Wheldon LM, Bereshchenko O, Bruscoli S, Kondrashov A, Drevet JR, Emes RD, Johnson AD, McCarrey JR, Gackowski D, Olinski R, Cocquet J, Garcia-Perez JL, Ruzov A. LINE-1 transcription in round spermatids is associated with accretion of 5-carboxylcytosine in their open reading frames. Commun Biol 2021; 4:691. [PMID: 34099857 PMCID: PMC8184969 DOI: 10.1038/s42003-021-02217-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 05/14/2021] [Indexed: 12/12/2022] Open
Abstract
Chromatin of male and female gametes undergoes a number of reprogramming events during the transition from germ cell to embryonic developmental programs. Although the rearrangement of DNA methylation patterns occurring in the zygote has been extensively characterized, little is known about the dynamics of DNA modifications during spermatid maturation. Here, we demonstrate that the dynamics of 5-carboxylcytosine (5caC) correlate with active transcription of LINE-1 retroelements during murine spermiogenesis. We show that the open reading frames of active and evolutionary young LINE-1s are 5caC-enriched in round spermatids and 5caC is eliminated from LINE-1s and spermiogenesis-specific genes during spermatid maturation, being simultaneously retained at promoters and introns of developmental genes. Our results reveal an association of 5caC with activity of LINE-1 retrotransposons suggesting a potential direct role for this DNA modification in fine regulation of their transcription.
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Abakir A, Giles TC, Cristini A, Foster JM, Dai N, Starczak M, Rubio-Roldan A, Li M, Eleftheriou M, Crutchley J, Flatt L, Young L, Gaffney DJ, Denning C, Dalhus B, Emes RD, Gackowski D, Corrêa IR, Garcia-Perez JL, Klungland A, Gromak N, Ruzov A. N 6-methyladenosine regulates the stability of RNA:DNA hybrids in human cells. Nat Genet 2019; 52:48-55. [PMID: 31844323 PMCID: PMC6974403 DOI: 10.1038/s41588-019-0549-x] [Citation(s) in RCA: 142] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 11/13/2019] [Indexed: 11/21/2022]
Abstract
R-loops are nucleic acid structures formed by an RNA:DNA hybrid and unpaired single stranded DNA that represent a source of genomic instability in mammalian cells1–4. Here we show that N6-methyladenosine (m6A) modification, contributing to different aspects of mRNA metabolism5, 6, is detectable on the majority of RNA:DNA hybrids in human pluripotent stem cells (hPSCs). We demonstrate that m6A-containing R-loops accumulate during G2/M and are depleted at G0/G1 phases of the cell cycle and that the m6A reader promoting mRNA degradation, YTHDF27, interacts with R-loops-enriched loci in dividing cells. Consequently, YTHDF2 knockout leads to increased R-loop levels, cell growth retardation and accumulation of γH2AX, a marker for DNA double-strand breaks, in mammalian cells. Our results suggest that m6A regulates accumulation of R-loops, implying a role for this modification in safeguarding genomic stability.
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Gackowski D, Gawronski M, Kerr C, Radivoyevitch T, Zarakowska E, Starczak M, Abakir A, Ruzov A, Maciejewski JP, Olinski R. 5-formylcytosine and 5-hydroxymethyluracil as surrogate markers of TET2 and SF3B1 mutations in myelodysplastic syndrome, respectively. Haematologica 2019; 105:e213-e215. [PMID: 31488558 DOI: 10.3324/haematol.2019.224030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
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Ramsawhook AH, Lewis LC, Eleftheriou M, Abakir A, Durczak P, Markus R, Rajani S, Hannan NRF, Coyle B, Ruzov A. Immunostaining for DNA Modifications: Computational Analysis of Confocal Images. J Vis Exp 2017:56318. [PMID: 28930980 PMCID: PMC5752195 DOI: 10.3791/56318] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
For several decades, 5-methylcytosine (5mC) has been thought to be the only DNA modification with a functional significance in metazoans. The discovery of enzymatic oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) as well as detection of N6-methyladenine (6mA) in the DNA of multicellular organisms provided additional degrees of complexity to the epigenetic research. According to a growing body of experimental evidence, these novel DNA modifications may play specific roles in different cellular and developmental processes. Importantly, as some of these marks (e. g. 5hmC, 5fC and 5caC) exhibit tissue- and developmental stage-specific occurrence in vertebrates, immunochemistry represents an important tool allowing assessment of spatial distribution of DNA modifications in different biological contexts. Here the methods for computational analysis of DNA modifications visualized by immunostaining followed by confocal microscopy are described. Specifically, the generation of 2.5 dimension (2.5D) signal intensity plots, signal intensity profiles, quantification of staining intensity in multiple cells and determination of signal colocalization coefficients are shown. Collectively, these techniques may be operational in evaluating the levels and localization of these DNA modifications in the nucleus, contributing to elucidating their biological roles in metazoans.
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Abakir A, Wheldon L, Johnson AD, Laurent P, Ruzov A. Detection of Modified Forms of Cytosine Using Sensitive Immunohistochemistry. J Vis Exp 2016:54416. [PMID: 27585398 PMCID: PMC5091899 DOI: 10.3791/54416] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Methylation of cytosine bases (5-methylcytosine, 5mC) occurring in vertebrate genomes is usually associated with transcriptional silencing. 5-hydroxylmethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) are the recently discovered modified cytosine bases produced by enzymatic oxidation of 5mC, whose biological functions remain relatively obscure. A number of approaches ranging from biochemical to antibody based techniques have been employed to study the genomic distribution and global content of these modifications in various biological systems. Although some of these approaches can be useful for quantitative assessment of these modified forms of 5mC, most of these methods do not provide any spatial information regarding the distribution of these DNA modifications in different cell types, required for correct understanding of their functional roles. Here we present a highly sensitive method for immunochemical detection of the modified forms of cytosine. This method permits co-detection of these epigenetic marks with protein lineage markers and can be employed to study their nuclear localization, thus, contributing to deciphering their potential biological roles in different experimental contexts.
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Eleftheriou M, Pascual AJ, Wheldon LM, Perry C, Abakir A, Arora A, Johnson AD, Auer DT, Ellis IO, Madhusudan S, Ruzov A. 5-Carboxylcytosine levels are elevated in human breast cancers and gliomas. Clin Epigenetics 2015; 7:88. [PMID: 26300993 PMCID: PMC4546187 DOI: 10.1186/s13148-015-0117-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 07/24/2015] [Indexed: 03/05/2023] Open
Abstract
BACKGROUND DNA methylation (5-methylcytosine (5mC)) patterns are often altered in cancers. Ten-eleven translocation (Tet) proteins oxidise 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). In addition to their presumptive specific biological roles, these oxidised forms of 5mC may serve as intermediates in demethylation process. According to several reports, 5hmC levels are strongly decreased in cancers; however, the distribution of 5fC and 5caC in malignant tissue has not been studied. FINDINGS Here, we examine the levels of 5hmC and 5caC in 28 samples of normal breast tissue, 59 samples of invasive human breast cancer and 74 samples of gliomas using immunochemistry. In agreement with previous reports, we show that 71 % of normal breast samples exhibit strong 5hmC signal, compared with only 18 % of breast cancer samples with equivalent levels of 5hmC staining. Unexpectedly, although 5caC is not detectable in normal breast tissue, 27 % of breast cancer samples exhibit significant staining for this modification (p < 0.001). Surprisingly, the presence of immunochemically detectable 5caC is not associated with the intensity of 5hmC signal in breast cancer tissue. In gliomas, we show that 5caC is detectable in 45 % of tumours. CONCLUSIONS We demonstrate that, unlike 5hmC, the levels of 5caC are elevated in a proportion of breast cancers and gliomas. Our results reveal another level of complexity to the cancer epigenome, suggesting that active demethylation and/or 5caC-dependent transcriptional regulation are pre-activated in some tumours and may contribute to their pathogenesis. Larger studies to evaluate the clinicopathological significance of 5caC in cancers are warranted.
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Wheldon LM, Abakir A, Ferjentsik Z, Dudnakova T, Strohbuecker S, Christie D, Dai N, Guan S, Foster JM, Corrêa IR, Loose M, Dixon JE, Sottile V, Johnson AD, Ruzov A. Transient accumulation of 5-carboxylcytosine indicates involvement of active demethylation in lineage specification of neural stem cells. Cell Rep 2014; 7:1353-1361. [PMID: 24882006 DOI: 10.1016/j.celrep.2014.05.003] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 04/04/2014] [Accepted: 05/02/2014] [Indexed: 01/22/2023] Open
Abstract
5-Methylcytosine (5mC) is an epigenetic modification involved in regulation of gene activity during differentiation. Tet dioxygenases oxidize 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Both 5fC and 5caC can be excised from DNA by thymine-DNA glycosylase (TDG) followed by regeneration of unmodified cytosine via the base excision repair pathway. Despite evidence that this mechanism is operative in embryonic stem cells, the role of TDG-dependent demethylation in differentiation and development is currently unclear. Here, we demonstrate that widespread oxidation of 5hmC to 5caC occurs in postimplantation mouse embryos. We show that 5fC and 5caC are transiently accumulated during lineage specification of neural stem cells (NSCs) in culture and in vivo. Moreover, 5caC is enriched at the cell-type-specific promoters during differentiation of NSCs, and TDG knockdown leads to increased 5fC/5caC levels in differentiating NSCs. Our data suggest that active demethylation contributes to epigenetic reprogramming determining lineage specification in embryonic brain.
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Alioui A, Wheldon LM, Abakir A, Ferjentsik Z, Johnson AD, Ruzov A. 5-Carboxylcytosine is localized to euchromatic regions in the nuclei of follicular cells in axolotl ovary. Nucleus 2012; 3:565-9. [PMID: 23138778 PMCID: PMC3515539 DOI: 10.4161/nucl.22799] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
5-Methylcytosine (5-mC) is an epigenetic modification associated with gene repression. Recent studies demonstrated that 5-mC can be enzymatically oxidised into 5-hydroxymethylcytosine and further into 5-formylcytosine (5-fC) and 5-carboxylcytsine (5-caC). 5-caC has been found in embryonic stem cells and in mouse pre-implantation embryos but no detectable levels of this modification have been reported for somatic tissues to date. Whereas it has been suggested that 5-caC can serve as an intermediate in the process of active demethylation, the function of this form of modified cytosine remains obscure. Here we show that 5-caC is immunochemically detectable in somatic cells of axolotl ovary. We demonstrate that both 5-hmC and 5-caC are localized to the euchromatin in the nuclei of axolotl follicular cells with similar patterns of spatial distribution. Our results suggest that 5-carboxylcytosine may play a distinct functional role in certain biological contexts.
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