Investigating Circadian Post-Transcriptional Regulation.

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Project Summary/Abstract: Circadian rhythms are highly conserved, 24-hour, oscillations that tune human physiology to the day/night cycle, enhancing fitness by ensuring that appropriate activities occur at biologically advantageous times. Disruption of proper circadian timing negatively impacts the human long-term medical outlook, making understanding the mechanism underlying circadian regulation over cellular physiology critical to human health. Circadian rhythms are controlled via a transcription-translation based negative feedback loop, or clock. The current paradigm for circadian regulation over physiology, termed the clocks “output”, is that transcriptional programing generated by the clock drives temporally-specific waves of gene expression. However, our research has revealed that transcriptional programing cannot wholly account for clock output, as we discovered weak correlation between mRNAs and proteins that oscillate with a circadian periodicity, particularly in the circadian regulation of immunometabolism. The mechanisms that control this post-transcriptional regulation are unknown, but we have shown that intrinsic protein disorder in the repressive complex of the clock may control the formation of macromolecular complexes to time clock output post-transcriptionally. Our immediate research goal is to identify specific pathways by which the clock imparts post- transcriptional control over the immune response at the biophysical, molecular, and physiological levels. We hypothesize that circadian post-transcriptional metabolic regulation can tune immune-tissue and sex-specific rhythms via the formation of time-of-day defined macromolecular protein complexes that are centered around the repressive complex of the circadian clock. To test this hypothesis, we will create a Conformational/Temporal Interactome (CiTI) map of circadian repressive complex proteins. We will also investigate the contribution of sex-specific metabolic post-transcriptional regulation to immune cell functions to demonstrate the effects of metabolic oscillations on the basal immune response. As a mechanism for keeping time, circadian feedback loops are highly conserved and much of what is understood about the molecular clock comes from the investigation of clock model systems. We will therefore exploit the simplicity and reproducibility of fungal and mammalian model systems to cost-effectively address our hypotheses. Due to the conservation of clock architecture, our findings will have the potential to define several novel and unrecognized paradigms in clock regulation over cellular physiology, including the sources and effects of circadian post-transcriptional regulation. These newly defined paradigms will further our long-term goal of elucidating the fundamental principles of circadian timing by identifying the mechanistic underpinnings of circadian control over cellular physiology.