DNA methylation errors in cloned mice disappear with advancement of aging.

Cloned animals have various health problems. Aberrant DNA methylation is a possible cause of the problems. Restriction landmark genomic scanning (RLGS) that enabled us to analyze more than 1,000 CpG islands simultaneously demonstrated that all cloned newborns had aberrant DNA methylation. To study whether this aberration persists throughout the life of cloned individuals, we examined genome-wide DNA methylation status of newborn (19.5 dpc, n=2), adult (8-11 months old, n=3), and aged (23-27 months old, n=4) cloned mice using kidney cells as representatives. In the adult and aged groups, cloning was repeated using cumulus cells of the adult founder clone of each group as nucleus donor. Two newborn clones had three with aberrantly methylated loci, which is consistent with previous reports that all cloned newborns had DNA methylation aberrations. Interestingly, we could detect only one aberrantly methylated locus in two of the three adult clones in mid-age and none of four senescent clones, indicating that errors in DNA methylation disappear with advancement of animals' aging.