Genome-wide profiling the epigenetic landscape of histone variant TH2B in murine oocytes and pre-implantation embryos [ChIP-seq]

The testis-specific histone variant of H2B, TH2B, is enriched in the oocytes, sperm and early embryos, with levels decreasing as the embryos differentiate into pre-gastrula stages. However, the involvement of TH2B in epigenetic reprogramming in the preimplantation embryos is largely unknown. The current study mapped the genome-wide epigenetics of TH2B in MII oocytes and early embryos using ultra-low-input ChIP-seq (ULI-ChIP). We demonstrate that TH2B deposition varies greatly between gametes; however, following fertilization, TH2B from gametes is swiftly redistributed in 2-cell embryos. A considerable enrichment of TH2B at the transcription start site (TSS) was identified in sperm chromatin compared to that in oocytes. We also found some overlap between the dynamics of the sperm and the 2 cell, which contain genes related to transcription regulation. Additionally, TH2B was enriched at zygotic genome activation (ZGA) genes. H2A.Z and TH2B were associated, as was discovered in the presence of H2AK119ub1. The correct execution of ZGA and other developmental programs, such as timing the expression or repression of particular genes, may involve TH2B along with H2A.Z, and H2AK119ub1, the latter two regulating the aforementioned processes. Also, early embryos had H3K9me3 deposited at TH2B-bound loci, which is a sign of heterochromatin and functions in regulating retrotransposons. In our study, we found that TH2B was enriched in LTRs. Thus, TH2B chromatin in gametes and preimplantation embryos has distinctive properties, as highlighted by our study, and they also present fresh opportunities to investigate the epigenetic dynamics in murine preimplantation embryos.