In addition to genetic manipulations, such as gene knockouts or single nucleotide changes, a growing number of diseases including cancer (Salarinia et al. 2016) and neurodegenerative (Gos 2013; Jakovcevski and Akbarian 2012; Landgrave-Gomez et al. 2015) diseases can be driven by changes in the epigenome of the cell. This can be both in terms of transcriptional levels, or for instance changes in DNA methylation patterns that may have more subtle effects, e.g. to alter how the cell responds to external signals. The impact and importance of such changes can be assessed by using nuclease-deficient forms of Cas9 fused to specific chromatin or DNA modifying factors (Fig. 4g). Two point mutations in the Cas9 protein (D10A, H840A) render it catalytically inactive, whilst retaining its ability to bind to specific DNA sequences. Fusion of domains to the Cas9 protein or binding to modified guide RNA scaffolds then allow recruitment of specific enzymatic activities to desired sites in the DNA (Dominguez et al. 2016; Konermann et al. 2013) (Fig. 4g). This has been used extensively to manipulate gene expression both positively using transcriptional
