Genome-wide analysis of sperm DNA methylation from monozygotic twin bulls

Monozygotic (MZ) twins are of great interest to elucidate the contributions of pre- and postnatal environmental factors on epigenetics in the expression of complex traits and diseases. Progeny testing recently revealed that MZ twin bulls do not necessarily lead to identical genetic merit estimates (i.e. breeding values). Therefore, to explain differences in offspring productivity of MZ twin bulls despite their identical genetic backgrounds, we hypothesised that paternal sperm epigenomes vary between MZ twin bulls. In the present study, semen characteristics and global sperm DNA methylome were profiled for four pairs of MZ twin bulls. Some MZ twin pairs had divergent semen quality (sperm morphology, motility and viability). Comparative genome-wide DNA methylome surveys were performed using methyl-sensitive enrichment and microarray identification. Between 2% and 10% of all probes (400000) were differentially methylated between MZ twin pairs. In addition, there were 580 loci differentially methylated across all pairs of MZ twins. Furthermore, enrichment analysis indicated a significant enrichment for fertility associated quantitative trait loci (P=0.033). In conclusion, differences in the sperm epigenome may contribute to incongruous diverging performances of daughters sired by bulls that are MZ twins.