In vitro postovulatory oocyte aging affects H3K9 trimethylation in two-cell embryos after IVF

Abstract Background The physiological time axis of oocytematuration comprises highly sensitive processes. A prolonged time span between ovulation and fertilization may impair oocytedevelopmental competence and subsequent embryo development, possibly due to epigenetic modifications. Since post-translational histone modifications can modify chromatin activity, and trimethylation of H3K9 (H3K9me3) has been shown to increase in the murine oocyteduring maturation, here the effect of postovulatory oocyteaging on H3K9me3 was analyzed. Methods The competence of murine oocyteswhich were aged for 2, 4, 6 and 8 hours in vitro after oocyteretrieval to develop to the two-cell and blastocyststage was determined. Degree of H3K9me3 was analyzed in the postovulatory aged oocytesas well as in the resulting two-cell embryos after IVF. Results The current study shows that postovulatory aging of oocytesfor up to eight hours after oocyteretrieval exhibited no effect on two-cell embryo and blastocystrate; however, changes in H3K9me3 in the resulting two-cell embryos were observed. Conclusion Prolonged postovulatory oocyteaging leads to epigenetic modifications of H3K9. Such modifications may affect the developmental capacity of embryos at post-implantation developmental stages.