Phosphorylation of histone H3 serine 10 in early mouse embryos: active phosphorylation at late S phase and differential effects of ZM447439 on first two embryonic mitoses.
ABSTRACT Cell division in mammalian cells is regulated by Aurora kinases. The activity of Aurora A is indispensable for correct function of centrosomes and proper spindle formation, while Aurora B for chromosome biorientation and separation. Aurora B is also responsible for the phosphorylation of histone H3 serine 10 (H3S10Ph) from G2 to metaphase. Data concerning the Aurora B activity and H3S10Ph in embryonic cells are limited to primordial and maturing oocytes and advanced pronuclei in zygotes. In the present study we have analyzed H3S10Ph in 1- and 2-cell mouse embryos. We show that H3S10 remains phosphorylated at anaphase and telophase of the second meiotic division, as well as during the anaphase and telophase of the first and second embryonic mitoses. At late G1 H3S10 is dephosphorylated and subsequently phosphorylated de novo at late S phase of the first and second cell cycle. These results show that the H3S10 phosphorylation/dephosphorylation cycle in embryonic cells is different than in somatic cells. The behaviour of thymocyte G0 nuclei introduced into ovulated oocytes and early 1-cell parthenogenotes confirms that kinases responsible for de novo H3S10 phosphorylation, most probably Aurora B, are active until G1 of the first cell cycle of mouse embryo. The inhibition of Aurora kinases by ZM447439 caused abnormalities both in the first and second mitoses. However, the disturbances in each division differed, suggesting important differences in the control of these mitoses. In ZM447439-treated mitotic zygotes Mad2 protein remained continuously present on kinetochores, what confirmed that spindle checkpoint remained active.
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ABSTRACT: Aryl hydrocarbon receptor (AHR) activation by xenobiotic ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is key to their toxicity. Following activation and nuclear translocation, AHR heterodimerizes with the AHR nuclear translocator (ARNT) and binds to AHR response elements (AhREs) in the enhancer of target genes, of which Cyp1a1 is the prototype. Previously, we showed that concomitant with AHR binding, histone H3 in the Cyp1a1 enhancer-promoter AhRE cluster became phosphorylated in serine-10 (H3S10), suggesting that the ligand-activated AHR recruited one or more kinases to the enhancer chromatin to phosphorylate this residue. To test this hypothesis, we used mouse hepatoma Hepa-1c1c7 cells and their c35 mutant derivative, lacking a functional AHR, to search for candidate kinases that would phosphorylate H3S10 in an AHR dependent manner. Using chromatin immunoprecipitation with antibodies to a comprehensive set of protein kinases, we identified three kinases, IKKα, MSK1 and MSK2, whose binding to the Cyp1a1 enhancer was significantly increased by TCDD in Hepa-1c1c7 cells and absent in control c35 cells. Complexes of AHR, ARNT and IKKα could be co-immunoprecipitated from nuclei of TCDD treated Hepa-1c1c7 cells, and shRNA-mediated IKKα knockdown inhibited both H3S10 phosphorylation in the Cyp1a1 enhancer and the induction of Cyp1a1, Aldh3a1 and Nqo1 in TCDD-treated cells. We conclude that AHR recruits IKKα to the promoter of its target genes and that AHR-mediated H3S10 phosphorylation is a key epigenetic requirement for induction of AHR targets. Given the role of H3S10ph in regulation of chromosome condensation, AHR-IKKα crosstalk may be a mediator of chromatin remodeling by environmental agents.Toxicological Sciences 02/2014; · 4.33 Impact Factor
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ABSTRACT: Epigenetic reprogramming of the parental genomes upon fertilization is required for proper embryonic development. It has long been appreciated that asymmetric distribution of histone modifications as well as differences in the level of DNA methylation exist between the parental pronuclei in mammalian zygotes and during preimplantation development. The speed at which the paternal genome is demethylated after entering the oocyte and the fact that rapid demethylation occurs in the absence of DNA replication have led many to hypothesize that a DNA demethylase must exist. However, such an enzyme has not been found. That the genome of mammalian preimplantation embryos undergo a wave of global demethylation was first reported 25 years ago but only in the past three years has data surfaced that can partially explain the elusive nature of this phenomenon. In addition to the global reorganization of the methylation and histone modification patterns, oocyte development prior to germinal vesicle breakdown involves the production of numerous small RNA, including miRNA. Despite their presence, miRNA functional activity is thought to be limited in the mature mouse oocyte. Additionally, molecular signatures in the 3' untranslated region of maternally expressed transcripts may impact mRNA stability during the transcriptionally quiescent period following germinal vesicle breakdown and prior to the maternal to zygote transition. In this review, we reference some of the recent works which attempt to shed light into the importance of the dynamic epigenetic landscape observed during oocyte maturation and preimplantation embryo development in mammals.Progress in Biophysics and Molecular Biology 02/2013; · 2.91 Impact Factor
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ABSTRACT: In mammals, epigenetic modifications are globally rearranged after fertilization, when gametes fuse to form the embryo. While gametes carry special epigenetic signatures and a unique nuclear organization, they attain embryo-specific patterns after fertilization. This "reprogramming" is promoted by intimate contact between the parental inherited genomes and the oocyte cytoplasm over the first cell cycles of development. Although the mechanisms of this reprogramming remain poorly understood, it appears that the particular epigenetic landscape established after fertilization is essential for further development. This review looks at histone post-translational modifications, focusing on their functions in chromatin organization and their role in nuclear architecture during mouse embryonic development. I also consider epigenetic changes linked to the use of assisted reproductive technologies. Mol. Reprod. Dev. © 2013 Wiley Periodicals, Inc.Molecular Reproduction and Development 10/2013; · 2.81 Impact Factor