Reproduction Abstracts

After fertilization, differentiated oocytes become totipotent embryos. In this transition, a drastic change in chromatin structure is known to occur, although the mechanism underlying this change remains to be elucidated. Recent studies have revealed that one of the major factors that contribute to the change in the chromatin structure is the exchange of histones with their variants. In mammals, there are three main non-centromeric histone H3 variants: H3.1, H3.2, and H3.3. Using transgenic mice and the microinjection method, we have previously shown that H3.3 is incorporated before and after fertilization. In contrast, there was limited incorporation of H3.1. However, the nuclear localization of H3.2 is not clarified. Here, using transgenic mice and microinjection method, we aim to investigate the role of H3 variants in embryonic development.

To examine the nuclear localization of H3.2, we generated transgenic mice that ubiquitously express Flag-tagged H3.2. Furthermore, to determine the biological significance of the composition of H3 variants at the 1-cell stage, we performed an overexpression analysis of H3.1, H3.2, and H3.3 to examine their effect in development.

We have found that H3.2 was not detected as well as H3.1 in 1-cell embryos, suggesting that H3.3 is the major histone variant incorporated at this stage. In addition, the embryos overexpressing H3.1 and H3.2 showed developmental delay and did not reach the blastocyst stage. These results suggest that limited incorporation of H3.1 and H3.2 into chromatin is essential for the change in chromatin structure at the 1-cell stage.