Post-transcriptional mechanisms in the Drosophila circadian clock – PostClock

Circadian clocks are present throughout the living world and control many aspects of physiology and behavior. For example, a brain circadian clock controls sleep-wake rhythms and receives light and temperature information to adapt the behavior to day-night cycles. Alterations of the day-night environment (example: shift work) cause disruptions in the circadian system with profound deleterious effects on health. At the molecular level, the circadian oscillator is based on a negative transcriptional feedback loop. The activating and repressing components of the loop are precisely regulated in terms of levels and activity to obtain a 24-hour cycle. In Drosophila, the transcription factors Clock and Cycle activate in the evening the expression of the genes encoding the Period and Timeless repressors, whose slow nocturnal accumulation leads to a phase of transcriptional repression at the end of the night. The temporal regulation of the accumulation of the repressors is a key element of the circadian oscillator and is based on the control of transcriptional activation as well as on a multitude of post-translational controls affecting Per and Tim. The contribution of post-transcriptional controls to this accumulation and its adaptation to day-night cycles is largely unknown.
The PostClock project aims to fill this gap by characterizing new post-transcriptional mechanisms in the brain clock that controls Drosophila behavioral rhythms. It associates two partners with highly complementary expertise on neurogenetics of circadian rhythms and epitranscriptomics. Our research program aims to understand how different types of post-transcriptional mechanisms (control of mRNA polyadenylation, mRNA methylation) contribute to circadian oscillations of mRNAs and proteins, and interact with transcription mechanisms. Based on our recent work, the first objective of the project will be to understand the mechanisms of regulation of mRNA polyadenylation that play an important role in establishing protein oscillations (objective 1). We will then seek to understand how Per controls the polyadenylation of tim mRNA, an unexpected discovery that highlights a new function of this transcriptional repressor, which we will also study through the analysis of tim mRNA methylation (objective 2). Finally, we propose to analyze the role of mRNA modifications (in particular m6A methylation) at the transcriptome level and to study their effects on the control of protein circadian oscillations as well as behavioral rhythms (objective 3).