Synchronizing the Neurospora crassa circadian clock with the rhythmic environment

Abstract

The metronomic predictability of the environment has elicited strong selection pressures for the evolution of endogenous circadian clocks. Circadian clocks drive molecular and behavioural rhythms that approximate the 24 h periodicity of our environment. Found almost ubiquitously among phyla, circadian clocks allow preadaptation to rhythms concomitant with the natural cycles of the Earth. Cycles in light intensity and temperature for example act as important cues that couple circadian clocks to the environment via a process called entrainment. This review summarizes our current understanding of the general and molecular principles of entrainment in the model organism Neurospora crassa, a simple eukaryote that has one of the best-studied circadian systems and light-signalling pathways.

Light input and processing in the circadian clock of Neurospora

“…Zeitgebers are used to synchronise the endogenous clock with the geophysical cycle of day and night, a process called entrainment. To entrain circadian clocks, light activates photoreceptors and information is integrated via signal transduction pathways into the central oscillating unit, which in eukaryotes is constituted by a transcriptional and translational autoregulatory feedback loop [1–5]. In the ascomycete Neurospora crassa – an intensively studied model organism for circadian clocks – light resetting of the clock is achieved via activation of the blue light receptor White Collar‐1 (WC‐1), which is a subunit of the heterodimeric clock transcription factor White Collar Complex (WCC) [6].…”

Detection and response of the Neurospora crassa circadian clock to light and temperature

“…The rapid induction or degradation of central clock components by brief light pulses has been used to explain clock resetting and entrainment to brief light pulses in other organisms (Shigeyoshi et al, 1997;Young and Kay, 2001; Ashmore and Sehgal, 2003). However, several lines of evidence suggest that clock entrainment to continuous photoperiods, as encountered in the real world, is more complex (Johnson et al, 2004;Tan et al, 2004;Elvin et al, 2005;Price-Lloyd et al, 2005). In Neurospora the ablation of qrf, an antisense transcript arising from the frq locus, or vivid (vvd ), a PAS/LOV-type photoreceptor, result in a much stronger resetting response to light pulses.…”