Regulation of zygotic gene activation by chromatin structure and epigenetic factors

After fertilization, the genomes derived from an oocyte and spermatozoon are in a transcriptionally silent state before becoming activated at a species-specific time. In mice, the initiation of transcription occurs at the mid-one-cell stage, which represents the start of the gene expression program. A recent RNA sequencing analysis revealed that the gene expression pattern of one-cell embryos is unique and changes dramatically at the two-cell stage. However, the mechanism regulating this alteration has not yet been elucidated. It has been shown that chromatin structure and epigenetic factors change dynamically between the one- and two-cell stages. In this article, we review the characteristics of transcription, chromatin structure, and epigenetic factors in one- and two-cell mouse embryos and discuss the involvement of chromatin structure and epigenetic factors in the alteration of transcription that occurs between these stages.