Intragenic DNA methylation prevents cryptic transcription initiations on gene bodies [ChIP-seq]

In mammals, DNA methylation occurs mainly at 5mC of CpG dinucleotides. The methylation on the promoter leads to the suppression of gene expression, while the functional role of gene body DNA methylation in highly expressed genes has yet to be clarified. Here, we show that the Dnmt3b-dependent intragenic DNA methylation protects the gene body from RNA Polymerase II (RNA Pol II) spurious entry and cryptic transcription initiation. Using different genome-wide approaches, we demonstrate that loss of Dnmt3b leads to an increase of the RNA Pol II engagement within gene bodies and spurious intragenic transcription initiation events. Furthermore, inhibition of RNA Pol II spurious entry depends on the enzymatic activity of the Dnmt3b recruited by H3K36me3. Thus, elongating RNA Pol II triggers an epigenetic crosstalk that involves SetD2, H3K36me3, Dnmt3b, and DNA methylation to ensure gene transcription initiation fidelity with implications for intragenic hypomethylation in cancer. Overall design: Genome-wide analysis of Dnmt3b role in mouse ESCs using RNA-seq.