Np95 interacts with de novo DNA methyltransferases, Dnmt3a and Dnmt3b, and mediates epigenetic silencing of the viral CMV promoter in embryonic stem cells

Recent studies have indicated that nuclear protein of 95 kDa (Np95) is essential for maintaining genomic methylation by recruiting DNA methyltransferase (Dnmt) 1 to hemi‐methylated sites. Here, we show that Np95 interacts more strongly with regulatory domains of the de novo methyltransferases Dnmt3a and Dnmt3b. To investigate possible functions, we developed an epigenetic silencing assay using fluorescent reporters in embryonic stem cells (ESCs). Interestingly, silencing of the cytomegalovirus promoter in ESCs preceded DNA methylation and was strictly dependent on the presence of either Np95, histone H3 methyltransferase G9a or Dnmt3a and Dnmt3b. Our results indicate a regulatory role for Np95, Dnmt3a and Dnmt3b in mediating epigenetic silencing through histone modification followed by DNA methylation. Meilinger et al. expand upon our understanding of the maintenance of DNA methylation patterns by Np95/Uhrf1 through recruitment of the DNA methyltransferase Dnmt1. Their results show that Np95 also interacts with the de novo DNA methyltransferases Dnmt3a and 3b and that together with the histone H3 methyltransferase G9a, all four mediate CMV promoter silencing in embryonic stem cells by a process involving histone modification followed by DNA methylation.