DNA methylation profiling of young and old mouse spermatozoa

The establishment and maintenance of proper DNA methylation patterns in spermatozoa are indispensable for the accurate transmission of genetic information to the next generation. In this study, we conducted genome-scale DNA methylation profiling of spermatozoa obtained from C57BL/6 mice at 2, 4.5 and 17 months of age (2m, 4.5m and 17m). We found that there was little change in the DNA methylation patterns between 4.5m and 17m samples, whereas LINE-1 repeat elements showed slightly increased methylation levels in 17m samples. Interestingly, promoter regions of genes associated with spermatogenesis and meiosis and most of maternally methylation imprinting control regions (m-ICRs) had 5-10% higher methylation levels in 2m samples than in 4.5m or 17m samples. An analysis of individual sequence reads suggested that 2m samples contained a subset of spermatozoa with fully-methylated (60-100%) spermatogenesis- and meiosis-related promoters and/or m-ICRs. These results suggest that a subset of spermatozoa from 2m samples have DNA methylation errors.