Large conserved domains of low DNA methylation maintained by Dnmt3a

Margaret Goodell and colleagues report genome-wide mapping of 5-methylcytosine and 5-hydroxymethylcytosine in purified mouse hematopoietic stem cells. They identify large regions of low methylation with borders marked by 5-hydroxymethylcytosine. These borders become eroded in the absence of DNA methyltransferase 3a.