Engineering Synthetic Gene Circuits in Living Cells with CRISPR Technology

One of the goals of synthetic biology is to build regulatory circuits that control cell behavior, for both basic research purposes and biomedical applications. The ability to build transcriptional regulatory devices depends on the availability of programmable, sequence-specific, and effective synthetic transcription factors (TFs). The prokaryotic clustered regularly interspaced short palindromic repeat (CRISPR) system, recently harnessed for transcriptional regulation in various heterologous host cells, offers unprecedented ease in designing synthetic TFs. We review how CRISPR can be used to build synthetic gene circuits and discuss recent advances in CRISPR-mediated gene regulation that offer the potential to build increasingly complex, programmable, and efficient gene circuits in the future. Regulatory cascades and logic gates have been built in bacteria and in mammalian cells using CRISPR-dCas9-based transcriptional regulatory systems.Advances in CRISPR-mediated transcriptional regulation allow multiple genes to be modulated simultaneously, a vital feature for constructing complex regulatory circuits.Modified guide RNAs (gRNAs) enable increased levels of transcriptional regulation by CRISPR as well as bidirectional regulation - the ability to activate some target genes and repress others within the same cell. New methods for inducible circuit activation include expression of gRNAs from inducible promoters as well as activation of the dCas9 protein by light.