Effect of superovulation treatment on oocyte´s DNA methylation

Controlled ovarian stimulation is a necessary step in some assisted reproductive procedures allowing the collection of female gametes at a precise time and at a suitable amount needed for subsequent fertilization steps. However, studies in animals have shown many consequences of hormonal treatments over the oocyte. Several of these studies used comparisons between oocytes from different donors, which is known that may influence the response differently. In this work we propose the use of the bovine model where each animal served as its own control. DNA methylation profile of oocytes from pre-ovulatory unstimulated follicles (NS) was compared to oocytes from stimulated follicles (S), after single-cell whole genome bisulphite sequencing. Results show that global percentage of methylation was similar between groups but percentage of methylation was lower for non-stimulated oocytes in the imprinted genes APEG3, MEG3 and MEG9, and higher in TSSC4 when compared to stimulated oocytes. Differences were also found in CpGi of imprinted genes: higher methylation was found among NS oocytes in MEST (PEG1)), IGF2R, GNAS (SCG6), KvDMR1 ICR UMD and IGF2. In another region around IGF2 the methylation percentage was lower for NS oocytes when compared to S oocytes. Data drawn from this study might help to understand the molecular reasons of the appearance of certain syndromes in assisted reproductive technologies-derived offspring. DNA methylation profile of oocytes from pre-ovulatory unstimulated follicles (NS) was compared to oocytes from stimulated follicles (S), after single-cell whole genome bisulphite sequencing