Increasing Genome Editing Efficiency of Cas9 Nucleases by the Simultaneous Use of Transcriptional Activators and Histone Acetyltransferase Activator.

The CRISPR-Cas9 system shows diverse levels of genome editing activities on eukaryotic chromatin, and high-efficiency sgRNA targets are usually desired in application. In this study, we show that chromatin open status is a pivotal determinant of the Cas9 editing activity in mammalian cells, and increasing chromatin accessibility can efficiently improve Cas9 genome editing. However, the strategy that increases chromatin openness by fusing the VP64 transcriptional activation domain at the C-terminus of Cas9 can only promote genome editing activity slightly at most tested CRISPR-Cas9 targets in Lenti-X 293T cells. Under the enlightenment that histone acetylation increases eukaryotic chromatin accessibility, we developed a composite strategy to further improve genome editing by activating histone acetylation. We demonstrate that promoting histone acetylation using the histone acetyltransferase activator YF-2 can improve the genome editing by Cas9 and, more robustly, by the Cas9 transcriptional activator (Cas9-AD). This strategy holds great potential to enhance CRISPR-Cas9 genome editing and to enable broader CRISPR gRNA target choices for experiments in eukaryotes.