The chromatin remodelling protein LSH/HELLS regulates the amount and distribution of DNA hydroxymethylation in the genome

Ten-Eleven Translocation (TET) proteins convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) leading to a dynamic epigenetic state of DNA that can influence transcription and chromatin organization. While TET proteins interact with complexes involved in transcriptional repression and activation, the overall understanding of the molecular mechanisms involved in TET-mediated regulation of gene expression still remains limited. Here, we show that TET proteins interact with the chromatin remodelling protein lymphoid-specific helicase (LSH/HELLS) <i>in vivo</i> and <i>in vitro</i>. In mouse embryonic fibroblasts (MEFs) and embryonic stem cells (ESCs) knock out of <i>Lsh</i> leads to a significant reduction of 5-hydroxymethylation amount in the DNA. Whole genome sequencing of 5hmC in wild-type versus <i>Lsh</i> knock-out MEFs and ESCs showed that in absence of <i>Lsh</i>, some regions of the genome gain 5hmC while others lose it, with mild correlation with gene expression changes. We further show that differentially hydroxymethylated regions did not completely overlap with differentially methylated regions indicating that changes in 5hmC distribution upon <i>Lsh</i> knock-out are not a direct consequence of 5mC decrease. Altogether, our results suggest that LSH, which interacts with TET proteins, contributes to the regulation of 5hmC levels and distribution in MEFs and ESCs.