SRA

During mammalian development DNA methylation patterns need to be reset in primordial germ cells (PGC) and preimplantation embryos. However, many retro-transposons and imprinted genes are resistant to such global epigenetic reprogramming via hitherto undefined mechanisms. Here, we report that some of these sequences are immune to widespread erasure of DNA methylation in the mouse embryonic stem cells (mESCs) lacking de novo DNA methyltransferases. Persistence of DNA methylation at these loci in mESCs depends on the histone H3K9 methyltransferase Setdb1, as deletion of Setdb1 results in reduction of H3K9me3 and DNA methylation levels concomitant with an increase in 5-hydroxymethylation (5hmC). In addition, depletion of H3K9 methyltransferase G9a leads to genome-wide reduction of DNA methylation but to a lesser extent at the above sequences. Taken together, these data reveal that Setdb1 ensures the fidelity of DNA methylation at specific loci in mESCs, which may reflect mechanisms functioning in vivo during key developmental stages. Overall design: Examination of genome-wide DNA hydroxy-methylation status in 3 cell types.