Maternal EHMT2 is essential for homologous chromosome segregation by regulating Cyclin B3 in mouse oocytes

During oocyte growth, various epigenetic modifications gradually establish, accompanying by large amounts of mRNAs and proteins accumulate. However, progress has been slow regarding the relationship between epigenetic modification and meiosis. Here, using Gdf9-Cre to achieve oocyte-specific ablation of Ehmt2 (Euchromatic Histone Lysine Methyltransferase 2) from primordial follicle stage, we found that female mutant mice were infertile and oocyte-specific knockout of Ehmt2 caused the failure of homologous chromosome separation independent of persistently activated SAC during the first meiosis. Further studies revealed that lacking maternal Ehmt2 affected the transcriptional level of Ccnb3, and microinjection of exogenous Ccnb3 mRNA could partly rescue the failure of homologous chromosomes segregation. Of particular importance was that EHMT2 could directly interact with CCNB3, despite truncated the SET domain. Therefore, our findings highlight the novel function of maternal EHMT2 on the metaphase I-to-anaphase I transition in mouse oocyte: directly interacting with CCNB3 apart from regulating the transcription of Ccnb3. Overall design: DNA methylation sequencing and RNA-sequencing were performed on the Ehmt2 Gdf9-cre deleted and control group oocytes.