Editing DNA Methylation in vivo [RNA-Seq]

DNA methylation is an epigenetic mechanism essential for orchestrating gene expression. Precise editing of DNA methylation has emerged as a new method to dissect its biological function in a DNA sequence specific manner with great potential to treat human diseases. However, applications of DNA methylation editing are largely in vitro. An experimental system to systematically investigate in vivo DNA methylation editing is needed to reveal its full therapeutic potential. We generated two transgenic mouse lines carrying an inducible dCas9-Dnmt3a or dCas9-Tet1 editor to enable cell-type specific methylation editing in vivo. We demonstrated that targeted methylation of the Psck9 promoter in the liver of dCas9-Dnmt3a mice reduced Psck9 expression and lowered plasma low-density lipoprotein cholesterol level to reduce the risk for cardiovascular diseases. Targeted demethylation of the Mecp2 promoter by dCas9-Tet1 reactivated Mecp2 expression from the inactive X chromosome in the brain of Mecp2 heterozygous Rett syndrome mice, suggesting a promising therapeutic approach for Rett syndrome and other X-linked diseases. Genome-wide sequencing analysis showed no detectable off-target at the transcriptional level in the methylation edited mice. These results demonstrate the feasibility and versatility of methylation editing in vivo, to explore DNA methylation in normal physiology and develop treatments for human diseases.