The Roles Of Histone Aceylation In Oocyte Meiotic Maturation And Early Embryonic Development Programs In Mouse

Post-translational modifications on histone emerge as a prodominated determinant of epigenetics, which has been implicated in cell differentiation, cell oncogenesis and cell pluripotency had been annotated. Histone acetylation is one of the most important posttranslational modifications that contribute to transcriptional initiation and chromatin remodeling. It might be particularly significant for mammalian oocyte maturation and early embryo development. However, the functional relevance of histone acetylation during mammalian oocyte meiosis and embryonic development remain elusive.We deciphered the pattern histone acetylation during mouse oocyte meiotic maturation and embryo development.(1) We in vitro treated GV-stage oocytes with different concentrations, sodium butyrate(NaBu), a histone deacetylase inhibitor, up for 14 h. We found that low dose NaBu treatment(0.1, 0.5 and 1.0 mM) had no effect on oocyte meiotic maturation. However the rates of meiotic maturation in 5.0 mM and 10.0mM NaBu treated oocyte were significantly compromised 53.3±2.93% 、30.2±0.05% VS 78.2 ±5.72%(control group).These results indicated that NaBu can inhibit meiotic resumption of mouse oocytes in a dose-dependent manner.(2) To study the effects of Sodium butyrate on meiotic progression through GV to metaphase I. Oocytes were cultured in NaBu-free medium for 3h and followed an additional 5h in culture with 2.0mM NaBu. We found that chromosomes were aligned at the equator of with barral-sharped spindles incontrol oocyte after 8h in culture. In contrast, chromosomes were irregularly distributed with different in spindle morphology. Furthermore, we analyzed the phosphorylation status of MAPK. Notably, the levels of both ERK1/2 and p-ERK1/2 were downregulated significantly by NaBu treatment(P<0.05).We used immunofluorescent analysis technology to determine the acetylation of histone H3K9 expression pattern in early in vivo embryos(IVO), in vitro fertilization(IVF) embryos and parthenogenetic embryos(PS) respectively. Our results indicated that there was no difference in acetylation levels of histone H3K9 in 2-cell and 8-cell stage embryos in these three groups.However, in 4-cell embryos stage, IVO fluorescence intensity(0.76 ± 0.27) was significantly higher than that of PS embryos(0.29± 0.78)(P<0.05). In the morula and blastula stage embryos, the levels of acetylated H3K9 in IVF and PS embryos were significantly lower than that of IVO embryos(P<0.05). In 8-cell embryos stage, these three kinds of embryos, the acetylation histone H3K9 acetylation had reached the lowest levels. The fore mentioned results indicated acetylation of histone H3K9 dynamically changes during whole pre-implantation development.We also evaluated the effects of NaBu on IVF embryos development and histone acetylation related regulators including HDAC1, and pluripotency transcription factors(Pou5f1, Sox2) mRNA expression levels of were assessed as well.(1) Zygotes were treated with 2.0mM NaBu in KSOM+AA medium for 24 h. Compared with control group, there was no remarkable change in cleavage rate or morula rate. But in blastula embryos stage, therate of blastocysts was significantly higher than that of control group.(2) For embryos cultured in NaBu, the expression of HDAC1, Pou5f1 and Sox2 mRNA in 2-cell stage embryos were significantly increased(P<0.05).