Abstract
Synthetic biology involves the generation of logic circuits to create or control biological functions and behaviors by engineering interconnected genetic elements such as promoters, repressors, and transcriptional activators. CRISPR discovery, and its adaptations to mammalian cells, has made it the tool of choice in molecular biology and revolutionized genome engineering in biomedical sciences. Here, we describe an adaptation of a split Cas9 to generate synthetic logic gates to sense biological events. As proof-of-concept, the complementing halves of split Cas9 were placed under different promoters, one unique to cancer cells of epithelial origin (phCEA) and one universal promoter (pCMV). We used self-assembling inteins to reunite the halves when co-expressed. Only cancer cells with epithelial origin expressed both halves and activated a reporter becoming green fluorescent. We then investigated whether we could apply this system to the detection of biological processes such as epithelial to mesenchymal transition (EMT). We designed another logic gate where one halve is expressed only by cancer cells of epithelial origin, while the other is activated during EMT – under the control of TWIST1. Indeed, cells undergoing EMT were detected by the activation of the reporter. Finally, the split-Cas9 logic gate was applied as a sensor to detect cell-cell fusion events in multiple cell lines. Each cell type expressed only one halve of split Cas9, and only induction of fusion resulted in the appearance of multinucleated syncytia and the expression of the reporter system. The simplicity and flexibility of the split Cas9 system reported here can be integrated to many other cellular processes, not only as a sensor but as an actuator.
Competing Interest Statement
The authors have declared no competing interest.
