Asymmetrical deposition and modification of histone H3 variants are essential for zygote development.

The pericentromeric heterochromatin of one-cell embryos forms a unique, ring-like structure around the nucleolar precursor body, which is absent in somatic cells. Here, we found that the histone H3 variants H3.1 and/or H3.2 (H3.1/H3.2) were localized asymmetrically between the male and female perinucleolar regions of the one-cell embryos; moreover, asymmetrical histone localization influenced DNA replication timing. The nuclear deposition of H3.1/3.2 in one-cell embryos was low relative to other preimplantation stages because of reduced H3.1/3.2 mRNA expression and incorporation efficiency. The forced incorporation of H3.1/3.2 into the pronuclei of one-cell embryos triggered a delay in DNA replication, leading to developmental failure. Methylation of lysine residue 27 (H3K27me3) of the deposited H3.1/3.2 in the paternal perinucleolar region caused this delay in DNA replication. These results suggest that reduced H3.1/3.2 in the paternal perinucleolar region is essential for controlled DNA replication and preimplantation development. The nuclear deposition of H3.1/3.2 is presumably maintained at a low level to avoid the detrimental effect of K27me3 methylation on DNA replication in the paternal perinucleolar region.