Imperial College London

DrPetraHajkova

Faculty of MedicineInstitute of Clinical Sciences

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 3313 8264petra.hajkova Website

 
 
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Location

 

4006CRB (Clinical Research Building)Hammersmith Campus

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Summary

 

Publications

Publication Type
Year
to

43 results found

Benesova M, Trejbalova K, Kucerova D, Vernerova Z, Hron T, Amouroux R, Klezl P, Hajkova P, Hejnar Jet al., Overexpression of TET dioxygenases in seminomas associates with low levels of DNA methylation and hydroxymethylation, Molecular Carcinogenesis, ISSN: 1098-2744

Germ cell tumors and particularly seminomas reflect the epigenomic features of their parental primordial germ cells, including the genomic DNA hypomethylation and expression of pluripotent cell markers. Because the DNA hypomethylation might be a result of TET dioxygenase activity, we examined expression of TET1-3 enzymes and the level of their product, 5-hydroxymethylcytosine, in a panel of histologically characterized seminomas and non-seminomatous germ cell tumors. Expression of TET dioxygenase mRNAs was quantified by real-time PCR. TET1 expression and the level of 5-hydroxymethylcytosine were examined immunohistochemically. Quantitative assessment of 5-methylcytosine and 5-hydroxymethylcytosine levels was done by liquid chromatography-mass spectroscopy technique. We found highly increased expression of TET1 dioxygenase in most seminomas and a strong TET1 staining in seminoma cells. Is ocitrate dehydrogenase 1 and 2 mutations were not detected suggest ing the enzymatic activity of TET1. The levels of 5-methylcytosine and 5-hydroxymethylcytosine in seminomas were found decreased in comparison to non-seminoma to us germ cell tumors and healthy testicular tissue. We propose TET1 expression as a marker of seminoma and mixed germ cell tumor and we suggest that high levels of TET1 expression are associated with the maintenance of low DNA methylation levels in seminomas. This “anti-methylator” phenotype of seminomas is in contrast to the CpG island methylator phenotype observed in a fraction of tumors of various types.

JOURNAL ARTICLE

Benešová M, Trejbalová K, Kučerová D, Vernerová Z, Hron T, Szabó A, Amouroux R, Klézl P, Hajkova P, Hejnar Jet al., 2017, Overexpression of TET dioxygenases in seminomas associates with low levels of DNA methylation and hydroxymethylation., Mol Carcinog

Germ cell tumors and particularly seminomas reflect the epigenomic features of their parental primordial germ cells, including genomic DNA hypomethylation and expression of pluripotent cell markers. Because the DNA hypomethylation might be a result of TET dioxygenase activity, we examined expression of TET1-3 enzymes and the level of their product, 5-hydroxymethylcytosine, in a panel of histologically characterized seminomas and non-seminomatous germ cell tumors. Expression of TET dioxygenase mRNAs was quantified by real-time PCR. TET1 expression and the level of 5-hydroxymethylcytosine were examined immunohistochemically. Quantitative assessment of 5-methylcytosine and 5-hydroxymethylcytosine levels was done by the liquid chromatography-mass spectroscopy technique. We found highly increased expression of TET1 dioxygenase in most seminomas and strong TET1 staining in seminoma cells. Isocitrate dehydrogenase 1 and 2 mutations were not detected, suggesting the enzymatic activity of TET1. The levels of 5-methylcytosine and 5-hydroxymethylcytosine in seminomas were found decreased in comparison to non-seminomatous germ cell tumors and healthy testicular tissue. We propose that TET1 expression should be studied as a potential marker of seminomas and mixed germ cell tumors and we suggest that elevated expression of TET dioxygenase enzymes is associated with the maintenance of low DNA methylation levels in seminomas. This "anti-methylator" phenotype of seminomas is in contrast to the CpG island methylator phenotype observed in a fraction of tumors of various types. This article is protected by copyright. All rights reserved.

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Amouroux R, Nashun B, Shirane K, Nakagawa S, Hill PWS, D'Souza Z, Nakayama M, Matsuda M, Turp A, Ndjetehe E, Encheva V, Kudo NR, Koseki H, Sasaki H, Hajkova Pet al., 2016, De novo DNA methylation drives 5hmC accumulation in mouse zygotes, NATURE CELL BIOLOGY, Vol: 18, Pages: 225-+, ISSN: 1465-7392

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Eguizabal C, Herrera L, De Onate L, Montserrat N, Hajkova P, Belmonte JCIet al., 2016, Characterization of the Epigenetic Changes During Human Gonadal Primordial Germ Cells Reprogramming, STEM CELLS, Vol: 34, Pages: 2418-2428, ISSN: 1066-5099

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Leitch HG, Surani MA, Hajkova P, 2016, DNA (De)Methylation: The Passive Route to Naivety?, TRENDS IN GENETICS, Vol: 32, Pages: 592-595, ISSN: 0168-9525

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Nashun B, Hill PW, Hajkova P, 2015, Reprogramming of cell fate: epigenetic memory and the erasure of memories past., EMBO Journal, Vol: 34, Pages: 1296-1308, ISSN: 0261-4189

Cell identity is a reflection of a cell type-specific gene expression profile, and consequently, cell type-specific transcription factor networks are considered to be at the heart of a given cellular phenotype. Although generally stable, cell identity can be reprogrammed in vitro by forced changes to the transcriptional network, the most dramatic example of which was shown by the induction of pluripotency in somatic cells by the ectopic expression of defined transcription factors alone. Although changes to cell fate can be achieved in this way, the efficiency of such conversion remains very low, in large part due to specific chromatin signatures constituting an epigenetic barrier to the transcription factor-mediated reprogramming processes. Here we discuss the two-way relationship between transcription factor binding and chromatin structure during cell fate reprogramming. We additionally explore the potential roles and mechanisms by which histone variants, chromatin remodelling enzymes, and histone and DNA modifications contribute to the stability of cell identity and/or provide a permissive environment for cell fate change during cellular reprogramming.

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Nashun B, Hill PWS, Smallwood SA, Dharmalingam G, Amouroux R, Clark SJ, Sharma V, Ndjetehe E, Pelczar P, Festenstein RJ, Kelsey G, Hajkova Pet al., 2015, Continuous Histone Replacement by Hira Is Essential for Normal Transcriptional Regulation and De Novo DNA Methylation during Mouse Oogenesis, MOLECULAR CELL, Vol: 60, Pages: 611-625, ISSN: 1097-2765

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Amouroux R, McEwen KR, Hajkova P, 2014, Current technological advances in mapping new DNA modifications, Drug Discovery Today: Disease Models, Vol: 12, Pages: 15-26, ISSN: 1740-6757

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Hill PS, Amouroux R, Hajkova P, 2014, DNA demethylation, Tet proteins and 5-hydroxymethylcytosine in epigenetic reprogramming: An emerging complex story, GENOMICS, Vol: 104, Pages: 324-333, ISSN: 0888-7543

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Supek F, Lehner B, Hajkova P, Warnecke Tet al., 2014, Hydroxymethylated Cytosines Are Associated with Elevated C to G Transversion Rates, PLOS GENETICS, Vol: 10, ISSN: 1553-7390

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Leitch HG, McEwen KR, Turp A, Encheva V, Carroll T, Grabole N, Mansfield W, Nashun B, Knezovich JG, Smith A, Surani MA, Hajkova Pet al., 2013, Naive pluripotency is associated with global DNA hypomethylation, NATURE STRUCTURAL & MOLECULAR BIOLOGY, Vol: 20, Pages: 311-316, ISSN: 1545-9993

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McEwen KR, Leitch HG, Amouroux R, Hajkova Pet al., 2013, The impact of culture on epigenetic properties of pluripotent stem cells and pre-implantation embryos, BIOCHEMICAL SOCIETY TRANSACTIONS, Vol: 41, Pages: 711-719, ISSN: 0300-5127

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Piccolo FM, Bagci H, Brown KE, Landeira D, Soza-Ried J, Feytout A, Mooijman D, Hajkova P, Leitch HG, Tada T, Kriaucionis S, Dawlaty MM, Jaenisch R, Merkenschlager M, Fisher AGet al., 2013, Different Roles for Tet1 and Tet2 Proteins in Reprogramming-Mediated Erasure of Imprints Induced by EGC Fusion, MOLECULAR CELL, Vol: 49, Pages: 1023-1033, ISSN: 1097-2765

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Hajkova P, 2011, Epigenetic reprogramming in the germline: towards the ground state of the epigenome, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 366, Pages: 2266-2273, ISSN: 0962-8436

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Hajkova P, 2010, Epigenetic reprogramming - taking a lesson from the embryo, CURRENT OPINION IN CELL BIOLOGY, Vol: 22, Pages: 342-350, ISSN: 0955-0674

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Hajkova P, Jeffries SJ, Lee C, Miller N, Jackson SP, Surani MAet al., 2010, Genome-Wide Reprogramming in the Mouse Germ Line Entails the Base Excision Repair Pathway, SCIENCE, Vol: 329, Pages: 78-82, ISSN: 0036-8075

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Surani MA, Hajkova P, 2010, Epigenetic reprogramming of mouse germ cells toward totipotency., Cold Spring Harb Symp Quant Biol, Vol: 75, Pages: 211-218

Primordial germ cells (PGCs), the precursors of sperm and eggs, are the route to totipotency and require establishment of a unique epigenome in this lineage. The genetic program for PGC specification in the mouse also initiates epigenetic reprogramming that continues when PGCs migrate into the developing gonads. Among these later events is active and genome-wide DNA demethylation, which is linked to extensive chromatin remodeling. These extensive epigenetic changes erase most, if not all, of the existing epigenetic information, which resets the epigenome for totipotency. Recent evidence suggests that active DNA demethylation involves a base excision repair (BER) pathway. BER is mechanistically linked to DNA demethylation, but what triggers BER is currently under investigation. The methylated cytosine (5mC) could be modified by deamination or to 5hmC, which could induce BER. Detection of Tet1 expression specifically and coincidentally, at the time of BER in PGCs, suggests that conversion of 5mC to 5hmC might be involved, at least in part, during epigenetic reprogramming and DNA demethylation in germ cells.

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Tee W-W, Pardo M, Theunissen TW, Yu L, Choudhary JS, Hajkova P, Surani MAet al., 2010, Prmt5 is essential for early mouse development and acts in the cytoplasm to maintain ES cell pluripotency, GENES & DEVELOPMENT, Vol: 24, Pages: 2772-2777, ISSN: 0890-9369

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Gebert C, Wrenzycki C, Herrmann D, Groeger D, Thiel J, Reinhardt R, Lehrach H, Hajkova P, Lucas-Hahn A, Carnwath JW, Niemann Het al., 2009, DNA methylation in the IGF2 intragenic DMR is re-established in a sex-specific manner in bovine blastocysts after somatic cloning, GENOMICS, Vol: 94, Pages: 63-69, ISSN: 0888-7543

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Hajkova P, Ancelin K, Waldmann T, Lacoste N, Lange UC, Cesari F, Lee C, Almouzni G, Schneider R, Surani MAet al., 2008, Chromatin dynamics during epigenetic reprogramming in the mouse germ line, NATURE, Vol: 452, Pages: 877-U6, ISSN: 0028-0836

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Hayashi K, Lopes SMCDS, Kaneda M, Tang F, Hajkova P, Lao K, O'Carroll D, Das PP, Tarakhovsky A, Miska EA, Surani MAet al., 2008, MicroRNA Biogenesis Is Required for Mouse Primordial Germ Cell Development and Spermatogenesis, PLOS ONE, Vol: 3, ISSN: 1932-6203

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Surani MA, Durcova-Hills G, Hajkova P, Hayashi K, Tee WWet al., 2008, Germ Line, Stem Cells, and Epigenetic Reprogramming, CONTROL AND REGULATION OF STEM CELLS, Vol: 73, Pages: 9-15, ISSN: 0091-7451

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Tang F, Hajkova P, O'Carroll D, Lee C, Tarakhovsky A, Lao K, Surani MAet al., 2008, MicroRNAs are tightly associated with RNA-induced gene silencing complexes in vivo, BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS, Vol: 372, Pages: 24-29, ISSN: 0006-291X

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Surani MA, Hayashi K, Hajkova P, 2007, Genetic and epigenetic regulators of pluripotency., Cell, Vol: 128, Pages: 747-762, ISSN: 0092-8674

Genetic and epigenetic mechanisms regulate the transition from the totipotent zygote to pluripotent primitive ectoderm cells in the inner cell mass of mouse blastocysts. These pluripotent cells can be propagated indefinitely in vitro, underpinned by a unique epigenetic state. Following implantation of the blastocyst, diverse epigenetic modifiers control differentiation of pluripotent epiblast cells into somatic cells, while specification of germ cells requires repression of the somatic program. Regenerating totipotency during development of germ cells entails re-expression of pluripotency-specific genes and extensive erasure of epigenetic modifications. Increasing knowledge of key underlying mechanisms heightens prospects for creating pluripotent cells directly from adult somatic cells.

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Tang F, Kaneda M, O'Carroll D, Hajkova P, Barton SC, Sun YA, Lee C, Tarakhovsky A, Lao K, Surani MAet al., 2007, Maternal microRNAs are essential for mouse zygotic development., Genes Dev, Vol: 21, Pages: 644-648, ISSN: 0890-9369

MicroRNAs (miRNAs) have important roles in diverse cellular processes, but little is known about their identity and functions during early mammalian development. Here, we show the effects of the loss of maternal inheritance of miRNAs following specific deletion of Dicer from growing oocytes. The mutant mature oocytes were almost entirely depleted of all miRNAs, and they failed to progress through the first cell division, probably because of disorganized spindle formation. By comparing single-cell cDNA microarray profiles of control and mutant oocytes, our data are compatible with the notion that a large proportion of the maternal genes are directly or indirectly under the control of miRNAs, which demonstrates that the maternal miRNAs are essential for the earliest stages of mouse embryonic development.

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Ancelin K, Lange UC, Hajkova P, Schneider R, Bannister AJ, Kouzarides T, Surani MAet al., 2006, Blimp1 associates with Prmt5 and directs histone arginine methylation in mouse germ cells., Nat Cell Biol, Vol: 8, Pages: 623-630, ISSN: 1465-7392

Blimp1, a transcriptional repressor, has a crucial role in the specification of primordial germ cells (PGCs) in mice at embryonic day 7.5 (E7.5). This SET-PR domain protein can form complexes with various chromatin modifiers in a context-dependent manner. Here, we show that Blimp1 has a novel interaction with Prmt5, an arginine-specific histone methyltransferase, which mediates symmetrical dimethylation of arginine 3 on histone H2A and/or H4 tails (H2A/H4R3me2s). Prmt5 has been shown to associate with Tudor, a component of germ plasm in Drosophila melanogaster. Blimp1-Prmt5 colocalization results in high levels of H2A/H4 R3 methylation in PGCs at E8.5. However, at E11.5, Blimp1-Prmt5 translocates from the nucleus to the cytoplasm, resulting in the loss of H2A/H4 R3 methylation at the time of extensive epigenetic reprogramming of germ cells. Subsequently, Dhx38, a putative target of the Blimp1-Prmt5 complex, is upregulated. Interestingly, expression of Dhx38 is also seen in pluripotent embryonic germ cells that are derived from PGCs when Blimp1 expression is lost. Our study demonstrates that Blimp1 is involved in a novel transcriptional regulatory complex in the mouse germ-cell lineage.

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Durcova-Hills G, Hajkova P, Sullivan S, Barton S, Surani MA, McLaren Aet al., 2006, Influence of sex chromosome constitution on the genomic imprinting of germ cells., Proc Natl Acad Sci U S A, Vol: 103, Pages: 11184-11188, ISSN: 0027-8424

Germ cells in XY male mice establish site-specific methylation on imprinted genes during spermatogenesis, whereas germ cells in XX females establish their imprints in growing oocytes. We showed previously that in vitro, sex-specific methylation patterns of pluripotent stem cell lines derived from germ cells were influenced more by the sex chromosome constitution of the cells themselves than by the gender of the embryo from which they had been derived. To see whether the same situation would prevail in vivo, we have now determined the methylation status of H19 expressed from the maternal allele, and the expression and methylation status of a paternally expressed gene Peg3, in germ cells from sex-reversed and control embryos. For these imprinted genes, we conclude that the female imprint is a response of the germ cells to undergoing oogenesis, rather than to their XX chromosome constitution. Similarly, both our XY and our sex-reversed XX male germ cells clearly showed a male rather than a female pattern of DNA methylation; here, however, the sex chromosome constitution had a significant effect, with XX male germ cells less methylated than the XY controls.

JOURNAL ARTICLE

Gebert C, Wrenzycki C, Herrmann D, Gröger D, Reinhardt R, Hajkova P, Lucas-Hahn A, Carnwath J, Lehrach H, Niemann Het al., 2006, The bovine IGF2 gene is differentially methylated in oocyte and sperm DNA., Genomics, Vol: 88, Pages: 222-229, ISSN: 0888-7543

The insulin-like growth factor 2 gene (IGF2) encodes an essential growth factor and is imprinted in various mammalian species. Differentially methylated regions (DMRs) are often located within CpG islands and are critically involved in the regulation of monoallelic Igf2 expression in the mouse. Only partial sequence information is available for the bovine IGF2 gene and no DMR has currently been identified. The goal of this study was to identify a DMR within the bovine IGF2 gene as a prerequisite for further studies on gene-specific methylation patterns during preimplantation development. Here we describe the sequence analysis of a CpG-rich DNA fragment from the 5' untranslated region spanning exons and introns 4 and 5 and the identification of a previously unknown DMR in exon 10 of the bovine IGF2 gene. Bisulfite analysis revealed that this DMR is differentially methylated in mature oocytes and sperm. The identification of an intragenic DMR within a developmentally important gene such as the bovine IGF2 gene provides a useful tool to evaluate the methylation patterns of embryos derived in vivo and in vitro. Our study is the first report of a differentially methylated region in a bovine imprinted gene discovered by the analysis of female and male gametes.

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Miyoshi N, Barton SC, Kaneda M, Hajkova P, Surani MAet al., 2006, The continuing quest to comprehend genomic imprinting., Cytogenet Genome Res, Vol: 113, Pages: 6-11

The discovery of the phenomenon of genomic imprinting in mammals showed that the parental genomes are functionally non-equivalent. Considerable advances have occurred in the field over the past 20 years, which has resulted in the identification and functional analysis of a number of imprinted genes the expression of which is determined by their parental origin. These genes belong to many diverse categories and they have been shown to regulate growth, complex aspects of mammalian physiology and behavior. Many aspects of the mechanism of imprinting have also been elucidated. However, the reasons for the evolution of genomic imprinting remain enigmatic. Further research is needed to determine if there is any relationship between the apparently diverse functions of imprinted genes in mammals, and their role in human diseases. It also remains to be seen what common features exist amongst the diverse imprinting control elements. The mechanisms involved in the erasure and re-establishment of imprints should provide deeper insights into epigenetic mechanisms of wide general interest.

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Tang F, Hajkova P, Barton SC, Lao K, Surani MAet al., 2006, MicroRNA expression profiling of single whole embryonic stem cells., Nucleic Acids Res, Vol: 34

MicroRNAs (miRNAs) are a class of 17-25 nt non-coding RNAs that have been shown to have critical functions in a wide variety of biological processes during development. Recently developed miRNA microarray techniques have helped to accelerate research on miRNAs. However, in some instances there is only a limited amount of material available for analysis, which requires more sensitive techniques that can preferably work on single cells. Here we demonstrate that it is possible to analyse miRNA in single cells by using a real-time PCR-based 220-plex miRNA expression profiling method. Development of this technique will greatly facilitate miRNA-related research on cells, such as the founder population of primordial germ cells where rapid and dynamic changes occur in a few cells, and for analysing heterogeneous population of cells. In these and similar cases, our method of single cell analysis is critical for elucidating the diverse roles of miRNAs.

JOURNAL ARTICLE

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