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Genome-wide DNA methylation assessment in mouse oocytes: effects of in vitro growth, superovulation and sexual immaturity

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE128656 | GEO | 2019/12/23

REPOSITORIES: GEO

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Project description:Background: With the rapid development of assisted reproductive technology (ART), although ovulation induction has made great progress, the accompanying health risks should not be ignored. Epigenetic modifications play an important role during the development of gametes and embryos. Recently, the epigenetic abnormalities caused by superovulation have attracted increasing attention. The follicle-stimulating hormone (FSH) and human menopausal gonadotropin (hMG) are common gonadotropins used for superovulation and appropriate concentration of them might be necessary. However, there is still no systematic study on the similarities and differences of DNA methylation alterations induced by superovulation with different dosage of FSH/hMG at the single cell levels. Methods: In the current study, the different doses of FSH/hMG combined with (add hcg full name here) hCG were used in C57BL/6 strain female mice to get experimental group oocytes while naturally matured oocytes and superovulated oocytes with only hCG were respectively set as controls. Single-cell level DNA methylation sequencing was carried out to all the mature oocytes to investigate the effect of superovulation with different dosage of FSH/hMG on DNA methylation during oocyte maturation. Results: In this study, we found that the hypo differentially methylated regions (DMRs) number of FSH/hMG 200 IU group both increased significantly although the whole genome methylation pattern of mature oocytes derived from superovulation were unaffected as compared with the control matured oocytes, suggesting that high dosage of FSH/hMG might lead to increased genomic methylation instability. At the same time, some of the DMRs annotated genes related to oocyte quality and embryonic development potential were disturbed in all dosage of FSH/hMG group (including Twist2, Cdk1, Ntrk2, Slc22a4, Sstr2, Wnt2, Cntnap5a, Gm2087, Slc16a7, and so on) as well as the certain ones (containing Abcc3, Zfp532, Atp1a1, Zfp804a, and so on) were impaired after high dosage of gonadotropins. We speculated that the effect of superovulation on DNA methylation during oocyte maturation might be dose-dependent to a certain extent, and such effect might affect oocyte quality and embryonic development competency. Conclusions: The current study firstly analyzed the differential impacts of different doses of gonadotropins on single-cell level DNA methylation of mouse oocytes, indicating a dose-dependent effect of superovulation with FSH/hMG and hCG on the epigenetic variations in mouse oocytes. Furthermore, some important genes that play a critical role in oocyte quality and embryo development were indicated to form the possible molecular basis of the corresponding regulation. This study laid a foundation for evaluating the safety of superovulation and highlighted the need for more and further research into ART.

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Genome-wide DNA methylation assessment in mouse oocytes: effects of in vitro growth, superovulation and sexual immaturity

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