DNA methylation errors in cloned mouse sperm by evading germline barrier

The germline reprogramming barrier reset parental epigenetic modifications according to sex. Recent studies have revealed the complete and accurate DNA methylome of mice and humans by whole genome sequencing, providing an opportunity to assess the accuracy and reliability of the germline reprogramming barrier. We used the sperms of mice cloned from somatic cells as a model for this study, since this is frequently accompanied by epigenetic errors. We identified differentially methylated CpG sites using the shotgun bisulfite sequencing method combined with enrichment of target regions, as known as targeted methylome sequencing (TMS). In some cases, specific DNA methylation errors remained in the sperm genome: however, there was no evidence that these DNA methylation errors were transmitted to the sperm of offspring. These results suggest that epigenetic mutations resulting from embryo cloning are transmitted to the sperm genome by evading the germline reprogramming barrier.