Changes In Histone H2A Variants During Mouse Oocyte Growth And Pre-Implantation Embryos

Histone variants are central epigenetic modification in eukaryotic chromatin. Histone variants are used by the cell to build specialized nucleosomes by replacing canonical histones at different stages of the cell cycle and generating an architecturally and functionally distinct chromatin structure. The histone H2A family encompasses the greatest diversity of variants among core histones which can substitute canonical replication-dependent H2A.The replacement histone variants, including H2AZ, macroH2A, H2A-Bbd, and H2AX, are distinguished from the major H2A histones by their carboxyl-terminal tails that diverge in both length and sequence. Incorporation of these particular histone subtypes into nucleosomes has significant impacts on transcriptional activation, DNA repair, meiosis, and apoptosis. In this study, we examined global changes in histone H2A variants during mouse oocyte growth and pre-implantation embryos. The results indicated that:(1) H2A.Bbd, H2A.Z and MacroH2A.1 fluorescent signal absent in 1-,5-,10-and 15-day growing oocytes (except for H2A.Bbd at 5-day oocytes) chromatin. In contrast, H2A.Bbd, H2A.Z and MacroH2A.1 fluorescent signal increase at cytoplasm. At 20-day oocyte, the same H2A.Bbd, H2A.Z and MacroH2A.1 fluorescent signal detected in nuclear and cytoplasm. An intense signal for H2A.X persisted in these 1-,5-,10-,15-and 20-day oocytes chromatin. Histone H2A variants haven't localized at growing oocytes chromatin, except for H2A.X. Yet, histone H2A variants'mRNAs present in cytoplasm.(2) During oocytes meiosis, both H2A.Bbd and MacroH2A.1 distribute at GV oocyte chromatin, whereas the fluorescent signals were disappeared from GVBD and MⅡoocytes chromatin. At GV and GVBD oocytes chromatin, detected weak H2A.Z fluorescent signals, whereas not detected fluorescent signal in MⅡoocyte chromatin; Both H2A.X and H2A.X-S139 were detected throughout oocyte meiosis. Although, during GVBD and MⅡstage oocytes, some H2A variants haven't distributed in chromatin, that mRNA had present in cytoplasm. (3) Changes in histone H2A variants during NIH3T3 cell mitosis. H2A.Bbd disappeared from metaphase; during NIH3T3 cell mitosis have not detected MacroH2A.1 fluorescent signal. According to our results, histone H2A variants play important role at NIH3T3 cell mitosis.(4) Immunocytochemistry with specific antibodies against various histone H2A variants showed histone H2A variants fluorescence signals in pre-implantation embryos. In our studies, a very weak signal for H2A.Bbd present in 1-cell and 2-cell embryos chromatin. From 4-cell embryo to blastula detected intense H2A.Bbd signals; Very weak signals for MacroH2A.1 present in 1-cell embryos chromatin. From 4-cell embryo to morula detected intense MacroH2A.1 fluorescence signals, whereas not detected MacroH2A.1 fluorescence signal at blastula; An intense signal for H2A.X persisted in mouse pre-implantation embryos chromatin; at 1-cell embryo detected very intense signal for H2A.X-S139, whereas detected very weak signal at 2-cell embryo. From 4-cell embryo to morula detected intense H2A.X-S139 fluorescence signals, whereas at blastula not detected H2A.X-S139 fluorescence signal.In conclusion, histone H2A variants might play an important role in mouse oocytes grow, during mouse pre-implantation embryos, the regulation of meiosis progression in mouse oocytes and somatic cell mitosis.