CRISPR-dCas9 systems that are precisely activated by cell-specific information facilitate the development of smart sensors or therapeutic strategies. We report the development of an activatable dCas9 transcriptional circuit that enables sensing and silencing of mRNA in living cells using hybridization-mediated structure switching for gRNA activation. The gRNA is designed with the spacer sequence blocked by a hairpin structure, and mRNA hybridization induces gRNA structure switching and activates the transcription of reporter RNA. An mRNA sensor developed using a light-up RNA reporter shows high sensitivity and fast-response imaging ofsurvivinmRNA in cells under drug treatments and different cell lines. Furthermore, a feedback circuit is engineered by incorporating a small hairpin RNA in the reporter RNA, demonstrating a smart strategy for dynamic sensing and silencing ofsurvivinwith induced tumor cell apoptosis. This circuit illustrates a broadly applicable platform for the development of cell-specific sensing and therapeutic strategies.
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