Analysis of Methylation Patterns in Ejaculated Sperm from F1 Nellore-Angus Crossbred Bulls

Abstract

Methylation of the carbon 5 position of cytosine is a common epigenetic mark in vertebrates, and has been associated with male infertility. Methylation can be affected by environmental changes in utero and our long-term goal is to establish whether maternal nutrition affects the bovine sperm methylome and variation in male fertility. As a first step, our objective here was to establish the general pattern of methylation in ejaculated bovine spermatozoa. We performed whole genome bisulfite sequencing for five F1 Nellore-Angus crossbred bulls and ~50 Gb of sequence was obtained per sample. Sequences were aligned to a bisulfite-converted version of the UMD3.1 bovine reference assembly.

The average level of CpG methylation was 88.2% and the global methylation patterns for sperm from Angus-Nellore F1 bulls and Nellore-Angus F1 bulls were similar. Gene bodies were heavily methylated, whereas promoter and CpG island (CGI) tended to be unmethylated. For promoters with unmethylated CGI, there was enrichment for pathways associated with transcription. Some differentially methylated regions were identified between Angus-Nellore F1 bulls and Nellore-Angus F1 bulls. These data on the bovine sperm methylome also establish a baseline from which future work related to bovine male infertility can proceed.