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8 results found

Hill PWS, Leitch HG, Requena CE, Sun Z, Amouroux R, Roman-Trufero M, Borkowska M, Terragni J, Vaisvila R, Linnett S, Bagci H, Dharmalingham G, Haberle V, Lenhard B, Zheng Y, Pradhan S, Hajkova Pet al., 2018, Epigenetic reprogramming enables the transition from primordial germ cell to gonocyte, Nature, Vol: 555, Pages: 392-396, ISSN: 0028-0836

Gametes are highly specialized cells that can give rise to the next generation through their ability to generate a totipotent zygote. In mice, germ cells are first specified in the developing embryo around embryonic day (E) 6.25 as primordial germ cells (PGCs)1. Following subsequent migration into the developing gonad, PGCs undergo a wave of extensive epigenetic reprogramming around E10.5–E11.52,3,4,5,6,7,8,9,10,11, including genome-wide loss of 5-methylcytosine2,3,4,5,7,8,9,10,11. The underlying molecular mechanisms of this process have remained unclear, leading to our inability to recapitulate this step of germline development in vitro12,13,14. Here we show, using an integrative approach, that this complex reprogramming process involves coordinated interplay among promoter sequence characteristics, DNA (de)methylation, the polycomb (PRC1) complex and both DNA demethylation-dependent and -independent functions of TET1 to enable the activation of a critical set of germline reprogramming-responsive genes involved in gamete generation and meiosis. Our results also reveal an unexpected role for TET1 in maintaining but not driving DNA demethylation in gonadal PGCs. Collectively, our work uncovers a fundamental biological role for gonadal germline reprogramming and identifies the epigenetic principles of the PGC-to-gonocyte transition that will help to guide attempts to recapitulate complete gametogenesis in vitro.

Journal article

Fisher AG, 2016, Ordered chromatin changes and human X chromosome reactivation by cell fusion-mediated pluripotent reprogramming, Nature Communications, Vol: 7, ISSN: 2041-1723

Erasure of epigenetic memory is required to convert somatic cells towards pluripotency. Reactivation of the inactive X chromosome (Xi) has been used to model epigenetic reprogramming in mouse, but human studies are hampered by Xi epigenetic instability and difficulties in tracking partially reprogrammed iPSCs. Here we use cell fusion to examine the earliest events in the reprogramming-induced Xi reactivation of human female fibroblasts. We show that a rapid and widespread loss of Xi-associated H3K27me3 and XIST occurs in fused cells and precedes the bi-allelic expression of selected Xi-genes by many heterokaryons (30–50%). After cell division, RNA-FISH and RNA-seq analyses confirm that Xi reactivation remains partial and that induction of human pluripotency-specific XACT transcripts is rare (1%). These data effectively separate pre- and post-mitotic events in reprogramming-induced Xi reactivation and reveal a complex hierarchy of epigenetic changes that are required to reactivate the genes on the human Xi chromosome.

Journal article

Chiu FWY, Bagci H, Fisher AG, deMello AJ, Elvira KSet al., 2016, A microfluidic toolbox for cell fusion, Journal of Chemical Technology and Biotechnology, Vol: 91, Pages: 16-24, ISSN: 1097-4660

Cellular fusion is a key process in many fields ranging from historical gene mapping studies and monoclonal antibody production, through to cell reprogramming. Traditional methodologies for cell fusion rely on the random pairing of different cell types and generally result in low and variable fusion efficiencies. These approaches become particularly limiting where substantial numbers of bespoke one-to-one fusions are required, for example, for in-depth studies of nuclear reprogramming mechanisms. In recent years, microfluidic technologies have proven valuable in creating platforms where the manipulation of single cells is highly efficient, rapid and controllable. These technologies also allow the integration of different experimental steps and characterisation processes into a single platform. Although the application of microfluidic methodologies to cell fusion studies is promising, current technologies that rely on static trapping are limited both in terms of the overall number of fused cells produced and their experimental accessibility. Here we review some of the most exciting breakthroughs in core microfluidic technologies that will allow the creation of integrated platforms for controlled cell fusion at high throughput. © 2015 Society of Chemical Industry.

Journal article

Landeira D, Bagci H, Malinowski AR, Brown KE, Soza-Ried J, Feytout A, Webster Z, Ndjetehe E, Cantone I, Asenjo HG, Brockdorff N, Carroll T, Merkenschlager M, Fisher AGet al., 2015, Jarid2 coordinates nanog expression and PCP/Wnt signaling required for efficient ESC differentiation and early embryo development, Cell Reports, Vol: 12, Pages: 573-586, ISSN: 2211-1247

Jarid2 is part of the Polycomb Repressor complex 2 (PRC2) responsible for genome-wide H3K27me3 deposition. Unlike other PRC2-deficient embryonic stem cells (ESCs), however, Jarid2-deficient ESCs show a severe differentiation block, altered colony morphology, and distinctive patterns of deregulated gene expression. Here, we show that Jarid2−/− ESCs express constitutively high levels of Nanog but reduced PCP signaling components Wnt9a, Prickle1, and Fzd2 and lowered β-catenin activity. Depletion of Wnt9a/Prickle1/Fzd2 from wild-type ESCs or overexpression of Nanog largely phenocopies these cellular defects. Co-culture of Jarid2−/− with wild-type ESCs restores variable Nanog expression and β-catenin activity and can partially rescue the differentiation block of mutant cells. In addition, we show that ESCs lacking Jarid2 or Wnt9a/Prickle1/Fzd2 or overexpressing Nanog induce multiple ICM formation when injected into normal E3.5 blastocysts. These data describe a previously unrecognized role for Jarid2 in regulating a core pluripotency and Wnt/PCP signaling circuit that is important for ESC differentiation and for pre-implantation development.

Journal article

Brown KE, Bagci H, Soza-Ried J, Fisher AGet al., 2013, Atypical heterochromatin organization and replication are rapidly acquired by somatic cells following fusion-mediated reprogramming by mouse ESCs, CELL CYCLE, Vol: 12, Pages: 3253-3261, ISSN: 1538-4101

Journal article

Bagci H, Fisher AG, 2013, DNA Demethylation in Pluripotency and Reprogramming: The Role of Tet Proteins and Cell Division, CELL STEM CELL, Vol: 13, Pages: 265-269, ISSN: 1934-5909

Journal article

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

Journal article

Tsubouchi T, Soza-Ried J, Brown K, Piccolo FM, Cantone I, Landeira D, Bagci H, Hochegger H, Merkenschlager M, Fisher AGet al., 2013, DNA Synthesis Is Required for Reprogramming Mediated by Stem Cell Fusion, CELL, Vol: 152, Pages: 873-883, ISSN: 0092-8674

Journal article

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