Casilio-ME: Enhanced CRISPR-based DNA demethylation by RNA-guided coupling methylcytosine oxidation and DNA repair pathways

ABSTRACT We have developed a methylation editing toolbox, Casilio-ME , that enables not only RNA-guided methylcytosine editing by targeting TET1 to genomic sites, but also by co-delivering TET1 and protein factors that couple methylcytosine oxidation to DNA repair activities, and/or promote TET1 to achieve enhanced activation of methylation-silenced genes. Delivery of TET1 activity by Casilio-ME1 robustly altered the CpG methylation landscape of promoter regions and activated methylation-silenced genes. We augmented Casilio-ME1 to simultaneously deliver the TET1-catalytic domain and GADD45A ( Casilio-ME2 ) or NEIL2 ( Casilio-ME3 ) to streamline removal of oxidized cytosine intermediates to enhance activation of targeted genes. Using two-in-one effectors or modular effectors, Casilio-ME2 and Casilio-ME3 remarkably boosted gene activation and methylcytosine demethylation of targeted loci. We expanded the toolbox to enable a stable and expression-inducible system for broader application of the Casilio-ME platforms. This work establishes an advanced platform for editing DNA methylation to enable transformative research investigations interrogating DNA methylomes.