Abstract
Epigenetics refers to chemical modifications of histone proteins and DNA that can regulate the expression of genes. The human epigenome is altered dynamically during cell differentiation and aging, and many diseases are associated with aberrant epigenome patterning. Recent advances in CRISPR have led to the development of programmable tools to edit epigenetic modifications at targeted genomic loci, enabling precise rewriting of epigenetic modifications in human cells. CRISPR-based epigenome editors rely on catalytically dead Cas9 coupled with epigenetic modifiers that ultimately result in programmed repression or activation of targeted genes in mammalian genomes. Unlike traditional genome editing methods, epigenome editing does not require DNA breaks or changes in the human genome sequence and thus serves as a safer alternative to control gene expression. In this protocol, we highlight two different methods to perform dCas9-mediated epigenome editing in human cell lines using plasmid DNA transfections and nucleofection of mRNAs encoding CRISPR epigenome editors. We demonstrate programmable epigenome editing to transiently repress genes using CRISPR interference (CRISPRi) and for silencing genes durably for many weeks using CRISPRoff, a fusion of dCas9 to the KRAB domain and de novo DNA methyltransferase complex. We also provide guidance on quantitative methods to measure successful epigenome editing of target genes and key considerations on which epigenome editing tool to use, depending on experimental criteria.