Circadian clocks control a large number of daily processes in most organisms. These endogenous cellular timekeepers regulate rhythms in gene expression, physiology and behaviour and enable organisms to anticipate predictable environmental variations.
Circadian clocks are composed of a central oscillator and two signaling pathways: input pathways convey external signals to the oscillator, so that it can be synchronized with the environment and output pathways allow the oscillator to temporally regulate diverse cellular processes.
The ascomycete Neurospora crassa, instrumental to the history of molecular biology (See The Almighty Fungi: The Revolutionary Neurospora crassa), has one of the best-understood circadian systems, in which a molecular negative feedback loop involving FREQUENCY and the WHITE COLLAR (WCC) complex lies at its core. Briefly, the WCC directly activates transcription of frq, and levels of FRQ protein start then to build up. FRQ inhibits its own expression by modulating the activity of the WCC, which results in the daily oscillation of both the frq mRNA and protein levels, and ultimately, in the rhythmic expression of a variety of clock-controlled genes (ccgs).
Despite the extensive knowledge accumulated on the molecular basis of some eukaryotic oscillators, including Neurospora’s, and the identification of a number of ccgs, little is known about the mechanisms that allow central oscillators to temporally control gene expression and the activity of different clock targets.
In this post, I will discuss a fascinating article from the Bell-Pedersen lab aiming at characterizing circadian output pathways in Neurospora.
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