GSE128656
Genome-wide DNA methylation assessment in mouse oocytes: effects of in vitro growth, superovulation and sexual immaturity
There is legitimate concern over epigenetic abnormalities that could be induced by procedures applied during assisted reproduction, necessitating epigenetic assessment of new methodologies. The effect of in vitro follicle culture (IFC) and superovulation on DNA methylation in the oocyte is not fully known. Here, we present the first genome-wide analysis of oocyte DNA methylation in IFC, superovulated mouse oocytes and, uniquely, we compare these data with naturally ovulated counterparts. Globally, the distinctive methylation landscape of oocytes, comprising alternating hyper- and hypomethylated domains, is preserved irrespective of the procedure. The conservation of methylation extends to the germline differential methylated regions (DMRs) of imprinted genes, necessary for their monoallelic expression in the embryo after fertilisation. However, we do detect specific, consistent and coherent differences in DNA methylation between IFC and oocytes from other groups, and between oocytes obtained after superovulation from pre-pubertal compared with sexually mature females. Several methylation differences span entire transcription units, consistent with effects on methylation downstream of transcriptional differences. Amongst these, we found alterations in Sox5, Zfp521 and Tcf4, genes for transcripton factors related to nervous system development. These observations also suggest transcriptional and epigenetic differences between oocytes from the initial and later phases of follicle recruitment. Our results provide an important reference for the use of in vitro growth and maturation, particularly from prepubertal females, in assisted reproductive technologies or fertility preservation. Overall design: 16 samples, 4 experimental groups: In vitro follicle culture (IFC, 4 samples); Superovulation prepubertal (SO, 5 samples), Superovulation Adult (SOA, 4 samples); In vivo (IV, 3 samples).