DNA methylation and mRNA expression profiles in bovine oocytes derived from prepubertal and adult donors

The developmental capacity of oocytes from prepubertal cattle is reduced compared to their adult counterparts and epigenetic mechanisms are thought to be involved herein. Here, we analysed DNA methylation in three developmentally important, non-imprinted genes (SLC2A1, PRDX1, ZAR1) and two satellite sequences, i.e. 'Bovine testis satellite I' and 'Bos taurus alpha satellite I'. In parallel, mRNA expression of the genes was determined by quantitative RT-PCR. Oocytes were retrieved from prepubertal calves and adult cows twice per week over a three weeks period by ultrasound guided follicular aspiration after treatment with FSH and/or IGF-1. Both immature and in vitro matured prepubertal and adult oocytes showed a distinct hypomethylation profile of the three genes without differences between the two types of donors. The methylation status of the Bovine testis satellite I sequence changed according to age and treatment while the methylation status of Bos taurus alpha satellite I sequence remained largely unchanged across the different age and treatment groups. Relative transcript abundance of the selected genes was significantly different in immature and in vitro matured oocytes; only minor changes related to origin and treatment were observed. In conclusion, methylation levels of the investigated satellite sequences were high (>50%) in all groups and showed significant variation depending on age, treatment or IVM. To what extent this is involved in the acquisition of developmental competence of bovine oocytes needs further study.