Repressed MERVL expression by increased HP1α causes developmental arrest in oxidatively damaged embryos

Background During in vitro fertilization (IVF), exposure to the in vitro environment and manual manipulation induces excessive accumulation of reactive oxygen species (ROS), leading to oxidative damage in embryos. The activation of embryonic totipotency is closely associated with epigenetic regulation. However, the molecular mechanisms by which oxidative damage alters the epigenetic landscape during zygotic genome activation (ZGA) remain largely unclear. This study aimed to investigate the epigenetic impact of oxidative damage on mouse two-cell stage embryos, a critical period for ZGA, and to identify key regulators involved. Results Using an established embryonic oxidative damage model, we demonstrated that oxidative damage impaired mouse embryonic totipotency and caused developmental arrest. Oxidative damage significantly altered the epigenetic marks H3K4me3 and H3K9me3 in mouse two-cell stage embryos. To dissect the underlying mechanisms, we employed CUT&Tag technology to profile H3K4me3 changes following oxidative damage. Our findings revealed a significant decrease in H3K4me3 distribution at promoters and transcription start sites (TSSs), and the biological functions associated with differentially marked regions were closely related to DNA damage repair, growth, and development. Further differential analysis revealed that H3K4me3 enrichment was significantly increased at the transcription start region of Cbx5 (encoding HP1α) after oxidative damage. By generating HP1α overexpression and knockdown embryonic models, we found that HP1α overexpression enhanced H3K9me3 enrichment and suppressed the expression of the totipotency marker MERVL, whereas HP1α knockdown exhibited the opposite effects. Moreover, knockdown of HP1α in H₂O₂-treated embryos reversed the oxidative-stress-induced increase in H3K9me3, reinstated MERVL transcription, and markedly improved the blastocyst formation rate. Conclusion In summary, our study highlights the importance of proper epigenetic reprogramming in embryonic development and identifies HP1α as a key player in oxidative damage-induced loss of embryonic totipotency. HP1α may therefore represent a novel therapeutic target for mitigating oxidative damage in embryos.