CRISPR/Cas9 represents a transformative and programmable tool to modify the genome. The endonuclease can be rendered inactive catalytically as dCas9 to further enable the modulation of the epigenetic landscape, through the recruitment of different effector molecules to the site of interest. For example, transcriptional activation can be achieved via tethering of transcriptional activators to dCas9. Fusion of single VP64 domain usually causes modest upregulation of gene, thus this leads to the development of several systems, which recruit multiple activators to potently activate gene transcription.
However, stably silenced genes that display a high level of CpG dinucleotide methylation are still refractory to the current generation of CRISPR activation systems. To counter this, we created an improved activation system by coupling the catalytic domain of DNA demethylating enzyme TET1 with transcriptional activators (TETact). TETact outperforms the current systems and induces transcription of heavily suppressed non-coding RNA and surface protein in differentiated cells.