Quantitative studies of mycobacterial single cell dynamics using a synthetic gene oscillator
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Abstract
The gene regulatory interaction network of Mycobacterium tuberculosis (Mtb) has been mostly reconstructed, resulting in a huge step towards revealing complicated interconnections between the network and cellular responses. Nevertheless, the temporal dynamics of gene expression in the regulatory network still remain unclear. Such information importantly provides further understandings in cellular behaviors underlying the system in the presence of external stresses such as those from the host immune system and drug treatments. Here I applied an engineering-based approach to the new context of studying the Mtb temporal dynamical system by adding a synthetic perturbation system. To do so, I developed the first synthetic gene oscillator functioning as a circadian clock in mycobacteria based on a transcriptional control circuit. The circuit encodes differentially-activated positive and negative feedback regulators, which enable autonomous, self-sustained oscillatory gene expression with an average period of 4.5 hours. I modeled robustness and tunability of oscillation period and amplitude computationally and verified them experimentally. I also used this oscillatory circuit transcriptionally to regulate one of the transcription factors (KstR), and profiled in vivo temporal dynamics of KstR and KstR-regulated gene targets by dual-color fluorescence intensities in single Mycobacterium smegmatics cells. I observed bifunctionality (activation and repression) of KstR-regulated gene expression, and different gene targets exhibited differential, characteristic response times. This constituted a proof-of-concept that one can utilize a genetic oscillator to characterize dynamical regulation of transcription factors underlying a complex regulatory system. Additionally, it presents a potential new strategy for using dynamical system modeling to guide genetic engineering of mycobacteria for future therapeutic applications.