Circadian Clocks

research1Circadian clocks generate the so-called circadian rhythms. Circadian rhythms are endogenous and self sustained 24 hours rhythms that drive most physiological and behavioral processes (i.e. sleep-wake cycles, alertness, body temperature, hormone release, etc).

Each single cell in our body posses a circadian clock that keeps time by using a complex transcriptional-translational feedback loop.

These loops have been first proposed and described to operate in Drosophila but later it was shown that a similar system is responsible for keeping circadian time in mammals.

In Drosophila, the master genes Clock (CLK) and cycle (CYC) activate the circadian system by promoting rhythmic transcription of several key clock genes (see right Figure).

Three of these target gene products, PER, TIM and CWO repress CLK-CYC mediated transcription on a daily basis. The CLK-CYC heterodimer also activates the expression of other activator-repressor pairs, for example VRI and PDP1, which are responsible for the oscillation of Clk mRNA.

These direct target genes are proposed to generate high amplitude mRNA oscillations in mammals and in flies. These feedback loops are also believed to underlie the oscillations of a large number of output mRNAs.