DNA CpG Methylation in High and Low Motile Sperm Populations in Bos taurus

Fertility is a major factor affecting economic efficiency in both milk and beef cattle production. Male fertility defects affect the ability of spermatozoa to fertilize and contribute to normal embryo development. Sperm epigenetics is an emerging area of study supported by observations that reported that abnormal sperm DNA methylation patterns are associated with infertility. Here, we explore cytosine-guanine dinucleotides (CpGs) methylation in Bos taurus high (HM) and low motile (LM) sperm populations separated by Percoll gradient.Two sperm populations (HM and LM) obtained from four bulls were evaluated for kinetic parameters by computer assisted sperm analysis (CASA). For each bull DNA methylation patterns were obtained on wide genomic regions by combining a methyl CpG DNA enrichment method and bisulfite genome sequencing. An average of 24.5 million sequence read pairs were generated per sample, over 87% of which were successfully mapped to the reference genome. The average level of methylated cytosine in CpG contest was about 94 %. Comparison between CpG island methylation in HM and LM sperm allowed to identify 297 genes overlapping regions that were differentially methylated (FDR <0.05). The characterization of the epigenome in Bos taurus sperm populations provides a first step towards the understanding of the effect of methylation on sperm fertility, also allowing to pinpoint key genes potentially associated to this trait.