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Nat Chem Biol. 2016 Nov;12(11):980-987. doi: 10.1038/nchembio.2179. Epub 2016 Sep 12.

A chemical-inducible CRISPR-Cas9 system for rapid control of genome editing.

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Genome Institute of Singapore, Agency for Science Technology and Research, Singapore.
School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore.
School of Biological Sciences, Nanyang Technological University, Singapore.
School of Life Sciences and Chemical Technology, Ngee Ann Polytechnic, Singapore.


CRISPR-Cas9 has emerged as a powerful technology that enables ready modification of the mammalian genome. The ability to modulate Cas9 activity can reduce off-target cleavage and facilitate precise genome engineering. Here we report the development of a Cas9 variant whose activity can be switched on and off in human cells with 4-hydroxytamoxifen (4-HT) by fusing the Cas9 enzyme with the hormone-binding domain of the estrogen receptor (ERT2). The final optimized variant, termed iCas, showed low endonuclease activity without 4-HT but high editing efficiency at multiple loci with the chemical. We also tuned the duration and concentration of 4-HT treatment to reduce off-target genome modification. Additionally, we benchmarked iCas against other chemical-inducible methods and found that it had the fastest on rate and that its activity could be toggled on and off repeatedly. Collectively, these results highlight the utility of iCas for rapid and reversible control of genome-editing function.

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