Hierarchical accumulation of histone variant H2A.Z regulates transcriptional states and histone modifications in early mammalian embryos [ChIP-seq]

Early embryos undergo extensive epigenetic reprogramming to achieve gamete-to-embryo transition, which involves the loading and removal of histone variant H2A.Z on chromatin. Although the H2A.Z landscapes in sperm have been investigated, its dynamics during early development remain unrevealed. Here, by using ultra-low-input native chromatin immunoprecipitation and sequencing (ULI-NChIP-seq), we map the genome-wide distribution of H2A.Z in mouse oocytes and early embryos. We find that paternal H2A.Z is removed upon fertilization, followed by unbiased accumulation on parental genomes during zygotic genome activation (ZGA). More importantly, H2A.Z exhibits hierarchical accumulation as different peak types at promoters. We identify that double H2A.Z peaks co-localizes with H3K4me3 and facilitates transcriptional activation, bivalent markers (H3K4me3+H3K27me3) prefer to occupy single H2A.Z peak and inhibits developmental gene expression, while promoters with no H2A.Z accumulation exhibit gene silencing in early embryos. Remarkably, H2A.Z depletion changes the enrichments of histone modifications and RNA polymerase II (Pol II) binding at promoters, resulting in abnormal gene expression and developmental arrest during lineage commitment. Hence, H2A.Z plays dual roles in regulating the epigenomes required for proper gene expression during preimplantation development.