BackgroundReactive oxygen species (ROS)-induced oxidative stress is well known to play a major role in male infertility. Sperm are sensitive to ROS damaging effects because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage. However, how oxidative DNA lesions in sperm affect early embryonic development remains elusive.ResultsUsing cattle as model, we show that fertilization using sperm exposed to oxidative stress caused a major developmental arrest at the time of embryonic genome activation. The levels of DNA damage response did not directly correlate with the degree of developmental defects. The early cellular response for DNA damage, γH2AX, is already present at high levels in zygotes that progress normally in development and did not significantly increase at the paternal genome containing oxidative DNA lesions. Moreover, XRCC1, a factor implicated in the last step of base excision repair (BER) pathway, was recruited to the damaged paternal genome, indicating that the maternal BER machinery can repair these DNA lesions induced in sperm. Remarkably, the paternal genome with oxidative DNA lesions showed an impairment of zygotic active DNA demethylation, a process that previous studies linked to BER. Quantitative immunofluorescence analysis and ultrasensitive LC–MS-based measurements revealed that oxidative DNA lesions in sperm impair active DNA demethylation at paternal pronuclei, without affecting 5-hydroxymethylcytosine (5hmC), a 5-methylcytosine modification that has been implicated in paternal active DNA demethylation in mouse zygotes. Thus, other 5hmC-independent processes are implicated in active DNA demethylation in bovine embryos. The recruitment of XRCC1 to damaged paternal pronuclei indicates that oxidative DNA lesions drive BER to repair DNA at the expense of DNA demethylation. Finally, this study highlighted striking differences in DNA methylation dynamics between bovine and mouse zygotes that will facilitate the understanding of the dynamics of DNA methylation in early development.ConclusionsThe data demonstrate that oxidative stress in sperm has an impact not only on DNA integrity but also on the dynamics of epigenetic reprogramming, which may harm the paternal genetic and epigenetic contribution to the developing embryo and affect embryo development and embryo quality.Electronic supplementary materialThe online version of this article (10.1186/s13072-018-0224-y) contains supplementary material, which is available to authorized users.

Naive pluripotency is established in preimplantation epiblast. Embryonic stem cells (ESCs) represent the immortalization of naive pluripotency. 2i culture has optimized this state, leading to a gene signature and DNA hypomethylation closely comparable to preimplantation epiblast, the developmental ground state. Here we show that Pramel7 (PRAME-like 7), a protein highly expressed in the inner cell mass (ICM) but expressed at low levels in ESCs, targets for proteasomal degradation UHRF1, a key factor for DNA methylation maintenance. Increasing Pramel7 expression in serum-cultured ESCs promotes a preimplantation epiblast-like gene signature, reduces UHRF1 levels and causes global DNA hypomethylation. Pramel7 is required for blastocyst formation and its forced expression locks ESCs in pluripotency. Pramel7/UHRF1 expression is mutually exclusive in ICMs whereas Pramel7-knockout embryos express high levels of UHRF1. Our data reveal an as-yet-unappreciated dynamic nature of DNA methylation through proteasome pathways and offer insights that might help to improve ESC culture to reproduce in vitro the in vivo ground-state pluripotency.

Background The use of sex-sorted sperm in cattle assisted reproduction is constantly increasing. However, sperm fertility can substantially differ between unsorted (conventional) and sex-sorted semen batches of the same sire. Sperm microRNAs (miRNA) have been suggested as promising biomarkers of bull fertility the last years. In this study, we hypothesized that the miRNA profile of cryopreserved conventional sperm is related to bull fertility after artificial insemination with X-bearing sperm. For this purpose, we analyzed the miRNA profile of 18 conventional sperm samples obtained from nine high- (HF) and nine low-fertility (LF) bulls that were contemporaneously used to produce conventional and sex-sorted semen batches. The annual 56-day non-return rate for each semen type (NRRconv and NRRss, respectively) was recorded for each bull. Results In total, 85 miRNAs were detected. MiR-34b-3p and miR-100-5p were the two most highly expressed miRNAs with their relative abundance reaching 30% in total. MiR-10a-5p and miR-9-5p were differentially expressed in LF and HF samples (false discovery rate < 10%). The expression levels of miR-9-5p, miR-34c, miR-423-5p, miR-449a, miR-5193-5p, miR-1246, miR-2483-5p, miR-92a, miR-21–5p were significantly correlated to NRRss but not to NRRconv. Based on robust regression analysis, miR-34c, miR-7859 and miR-342 showed the highest contribution to the prediction of NRRss. Conclusions A set of miRNAs detected in conventionally produced semen batches were linked to the fertilizing potential of bovine sperm after sex-sorting. These miRNAs should be further evaluated as potential biomarkers of a sire’s suitability for the production of sex-sorted sperm.