Dynamic replacement of H3.3 affects nuclear reprogramming in early bovine SCNT embryos

The histone variant H3.3 is an important maternal factor in fertilization of oocytes and reprogramming of somatic cell nuclear transfer (SCNT) embryos. As a crucial replacement histone, maternal H3.3 is involved in chromatin remodeling and zygote genome activation. Litte is, however, known about the replacement of H3.3 in the bovine SCNT embryos. In this study, the maternal H3.3 in mature ooplasm was labeled with HA tag and the donor cells H3.3 was labeled with Flag tag, in order to observe the replacement of H3.3 in the bovine SCNT embryos. Meanwhile, maternal H3.3 knockdown was performed by microinjecting two different interfering fragments before nucleus transfer. It was showed that the dynamic replacement between maternal- and donor nucleus-derived H3.3 was detected after SCNT. And it could be observed that the blastocyst development rate of the cloned embryos decreased from 22.3% to 8.2-10.3% (P < 0.05), the expression of Pou5f1 and Sox2 was down-regulated and the level of H3K9me3 was increased in the interfered embryos. In summary, H3.3 replacement impacted on the process of reprogramming, including embryonic development potential, activation of pluripotency genes and epigenetic modification in bovine SCNT embryos.