Maternal H3.3-Mediated Reprogramming of Parental Genomes during Minor Zygotic Genome Activation [RNA-seq]

Zygotic gene activation (ZGA) is the first transcription event in life, and is associated with extensive epigenetic reprogramming, which is involved with dynamic incorporation of histone variant H3.3. H3.3 plays essential roles during mouse pre-implantation development. However, the coexistence of distinct sources of H3.3 in early embryos, including paternal and maternal allele-expressed H3.3 (paH3.3 and maH3.3), complicates our ability to track their individual dynamics, which may have distinct roles in embryonic development. In this study, by taking advantage of our H3.3B-HA-tagged mouse model, we illustrated the paH3.3 and maH3.3 landscapes in mouse early embryos, and described the manner of maternal mRNAs-derived H3.3 (mH3.3) on paternal genome reprogramming. We found the deposition of mH3.3 is required for cleavage development and minor ZGA, mechanistically, by mH3.3S31p-meditated acetylation at lysine 27. And, we propose that the mH3.3K27ac modification displaces the repressive histone modifications, thus enabling the activation of minor ZGA genes. Taken together, we demonstrate the central role of mH3.3 in reprogramming parental genomes by establishment of H3K27ac.