Epigenetic Editing with CRISPR/Cas9
Epigenetic modifications to genomic DNA and histone proteins have been shown to play increasingly critical roles in biological processes. Epigenetic marks, such as methylation or acetylation, at specific genomic loci and histone residues can either be inherited or acquired, and can influence gene expression.
Recent studies have used CRISPR/Cas9 genome editing to investigate the roles and targets for these epigenetic marks. In one such study, researchers performed CRISPR-mediated knock out of all three active DNA methyltransferases present in human embryonic stem cells, to characterize viable, pluripotent cell lines and study the distinct effects on the DNA methylation landscape. But researchers increasingly need methods for introducing epigenetic modifications at desired genomic loci, in order to model diseases and test hypotheses regarding potential therapeutic strategies. For example, specific epigenetic alterations are often necessary and sufficient to drive the transformation of normal cells into cancerous cells, and play roles in later steps of carcinogenesis.
Using the CRISPR/Cas9 system, epigenetic editing has now become feasible. Utilizing inactive dCas9 as a DNA-binding domain platform, fused enzymes such as DNA methylases, histone acetyltransferases, and deacetylases, can be targeted to alter the epigenetic state at precise locations within the genome. Researchers have used this approach, to fuse the catalytic core of human acetyltransferase p300 with dCas9, and shown this system to be sufficient for acetylation of histone H3 lysine 27 at specific target sites and to robustly activate transcription of target genes. Cas9 epigenetic effectors (epiCas9s) can also be used for genome-wide screening to discover novel relationships between epigenetic modifications, chromatin states, and phenotypes such as, cellular differentiation or disease progression.