CHARM and EvoETR: Precision epigenetic tools for gene silencing

With the advent of gene editing technologies like CRISPR/Cas9, it has become possible to edit genomic regions of interest for research and therapeutic purposes. These technologies have also been adapted to alter gene expression without changing their DNA sequence, allowing epigenetic edits. While genetic editors make edits by cutting the genome at specified regions, epigenetic editors leverage the same targeting mechanism but act based on the epigenetic modifier fused to them, such as a methyltransferase. Here, we discuss two recently employed epigenetic editors (epi-editors) that silenced target genes involved in disease to mitigate their effects. Neumann et al. reported the construction of an epigenetic editor called CHARM that could methylate and silence the prion gene in mouse brains and subsequently switch itself off. Additionally, Capelluti et al. developed an epi-editor called EvoETR that knocked down Pcsk9 in the murine liver to reduce LDL levels. We aim to highlight the design principles underlying the design of these epi-editors to inform future editor designs.