miRNAs Are Required for Generating a Time Delay Critical for the Circadian Oscillator

Abstract

Background Circadian clocks coordinate an organism’s activities and regulate metabolic homeostasis in relation to daily environmental changes, most notably light/dark cycles. As in other organisms, the timekeeping mechanism in mammals depends on a self-sustaining transcriptional negative feedback loop with a built-in time delay in feedback inhibition. Although the time delay is essential for generating a slow, self-sustaining negative feedback loop with a period close to 24 hours, the exact mechanisms underlying the time delay are not known. Results We show here that RNA interference mediated by microRNAs (miRNAs) is an essential mechanism in generating the time delay. In Dicer-deficient (and thus miRNA-deficient) cells and mice, circadian rhythms were dramatically shortened (by ~2 hours), although the rhythms remained robust. The period shortening was caused by faster PER1 and PER2 translation in the Dicer-deficient cells. We also identified three specific miRNAs that regulate Per expression, and showed that knockdown of these miRNAs in wild-type cells also shortened the circadian period. Conclusions Consistent with the canonical function of miRNAs as translational modulators of target genes and their widespread roles in cell physiology, circadian rhythms are also modulated by miRNA-mediated RNA interference acting on posttranscriptional regulation of key clock genes. Our present study definitively shows that RNA interference is an important modulator of circadian rhythms by controlling the pace of PER synthesis, and presents a novel layer of regulation for the clock.

Relevance of Circadian Rhythm in Cancer

“…For instance, the duration of the cycle needs to have a period of completion close to 24 h. One feature of this process is that the translation of circadian mRNAs does not follow immediately after transcription; instead, there is an approximate 2-4 h delay between generation of the mRNA and protein synthesis. This delay is in part regulated via miRNA-dependent mechanisms, consistent with findings that DICER deficient cells exhibited a shortened circadian period length and had an associated acceleration on PER1 and PER2 translation [2]. In addition, the timing of individual steps and of the overall circadian cycle involves the extensive posttranslational regulation of oscillator components.…”

Chromatin landscape and circadian dynamics: Spatial and temporal organization of clock transcription

“…Genetic disruption of the microRNA (miRNA) pathway by mutating Dicer either in the mouse or in cell lines affects the circadian transcriptome (55,56). Indeed, hepatic miR-122 controls the phase and amplitude of several metabolic genes (57).…”

miR-124Regulates the Phase ofDrosophilaCircadian Locomotor Behavior

“…Dicer proteins are critical for miRNA biogenesis (Bartel, 2004). In Dicer-deficient mice, shortened circadian rhythms have been observed mainly because of faster translation of PERIOD1 and PERIOD2, two critical pacemaker proteins (Chen et al, 2013). In flies, knocking down DICER-1 decreases the amplitude of locomotor rhythms (Kadener et al, 2009).…”

“…Temperature increases also trigger TIM degradation to reset circadian clocks in flies, but this molecular response is mediated by calcium and the atypical protease SOL (Tataroglu et al, 2015). Circadian clock neurons can also receive thermal and photic inputs nonautonomously (HelfrichFörster et al, 2001;Chen et al, 2015). miRNAs are small, noncoding RNAs that regulate many important biological processes through posttranscriptional repression of specific target genes (Bartel, 2004).…”