Sperm DNA methylation patterns at discrete  CpGs and genes involved in embryonic  development are related to bull fertility

Background: Despite a multifactorial approach being taken for the evaluation of bull semen quality in many animal breeding centres worldwide, reliable prediction of bull fertility is still a challenge. Recently, attention has turned to molecular mechanisms, which could uncover potential biomarkers of fertility. One of these mechanisms is DNA methylation, which together with other epigenetic mechanisms is essential for the fertilising sperm to drive normal embryo development and establish a viable pregnancy. In this study, we hypothesised that bull sperm DNA methylation patterns are related to bull fertility. We therefore investigated DNA methylation patterns from bulls used in artifcial insemination with contrasting fertility scores.

Results: The DNA methylation patterns were obtained by reduced representative bisulphite sequencing from 10 high-fertility bulls and 10 low-fertility bulls, having average fertility scores of −6.6 and + 6.5%, respectively (mean of the population was zero). Hierarchical clustering analysis did not distinguish bulls based on fertility but did highlight individual diferences. Despite this, using stringent criteria (DNA methylation diference≥35% and a q-value <0.001), we identifed 661 diferently methylated cytosines DMCs). DMCs were preferentially located in intergenic regions, introns, gene downstream regions, repetitive elements, open sea, shores and shelves of CpG islands. We also identifed 10 diferently methylated regions, covered by 7 unique genes (SFRP1, STXBP4, BCR, PSMG4, ARSG, ATP11A, RXRA), which are involved in spermatogenesis and early embryonic development.

Conclusion: This study demonstrated that at specifc CpG sites, sperm DNA methylation status is related to bull fertility, and identifed seven diferently methylated genes in sperm of subfertile bulls that may lead to altered gene expression and potentially infuence embryo development.