Glycogen synthase kinase-3 (Gsk-3) plays a fundamental role in maintaining DNA methylation at imprinted loci in mouse embryonic stem cells

Glycogen synthase kinase-3 (Gsk-3) is a key regulator of multiple signal transduction pathways. Recently we described a novel role for Gsk-3 in the regulation of DNA methylation at imprinted loci in mouse embryonic stem cells (ESCs), suggesting that epigenetic changes regulated by Gsk-3 are likely an unrecognized facet of Gsk-3 signaling. Here we extend our initial observation to the entire mouse genome by enriching for methylated DNA with the MethylMiner kit and performing next-generation sequencing (MBD-Seq) in wild-type and Gsk-3α(-/-);Gsk-3β(-/-) ESCs. Consistent with our previous data, we found that 77% of known imprinted loci have reduced DNA methylation in Gsk-3-deficient ESCs. More specifically, we unambiguously identified changes in DNA methylation within regions that have been confirmed to function as imprinting control regions. In many cases, the reduced DNA methylation at imprinted loci in Gsk-3α(-/-);Gsk-3β(-/-) ESCs was accompanied by changes in gene expression as well. Furthermore, many of the Gsk-3-dependent, differentially methylated regions (DMRs) are identical to the DMRs recently identified in uniparental ESCs. Our data demonstrate the importance of Gsk-3 activity in the maintenance of DNA methylation at a majority of the imprinted loci in ESCs and emphasize the importance of Gsk-3-mediated signal transduction in the epigenome.