The expression and nuclear deposition of histone H3.1 in murine oocytes and preimplantation embryos.

Differentiated oocytes acquire totipotency through fertilization. During this transition, genome-wide chromatin remodeling occurs, which leads to change in gene expression. However, the mechanism that underlies this global change in chromatin structure has not been fully elucidated. Histone variants play a key role in defining chromatin structure and are implicated in inheritance of epigenetic information. In this study, we analyzed the nuclear localization and expression of H3.1 to elucidate the role of this histone variant in chromatin remodeling during oogenesis and preimplantation development. Analysis using Flag-tagged H3.1 transgenic mice revealed that Flag-H3.1 was not present in differentiated oocytes or early preimplantation embryos before the morula stage, although Flag-H3.1 mRNA was expressed at all stages examined. In addition, the expression levels of endogenous H3.1 genes were low at the stages where H3.1 was not present in chromatin. These results suggest that H3.1 is not incorporated into chromatin due to the inactivity of the histone chaperone and low mRNA expression level. The significance of the dynamics of H3.1 is evaluated in terms of chromatin remodeling that takes place during development.