Anita Szőke1, Norbert Gyöngyösi1, Krisztina Ella1, Ágnes Sűdy1 and Krisztina Káldi1,2
1Department of Physiology, Semmelweis University, Budapest
2Department of Laboratory Medicine, Semmelweis University, Budapest
The metabolic regulation of the circadian clock has been investigated for a long time, however the underlying mechanism is still not completely understood. Metabolic compensation allows the circadian oscillator to keep a nearly constant period in an environment with changing substrate levels.
As RAS2-mediated signalling plays a central role in the adaptation of yeast to different nutritional environments, we examined the involvement of the RAS-mediated pathway in the metabolic regulation of the clock in the circadian model organism Neurospora crassa. We found that in the ras2-deficient strain the period was longer than in the control and operation of the circadian clock was affected by glucose. In contrast to the wt, in ∆ras2 the period become longer and the oscillation of the expression of the frequency (frq) gene showed dampening in the presence of glucose. In accordance with the longer period and the less robust rhythm of the mutant, both phosphorylation and nuclear clearance of the FRQ protein were delayed in constant darkness. Whereas glucose did not affect the subcellular distribution of FRQ in wt, elevated FRQ levels were detected in Δras2 nuclei. Interaction of RAS2 with the RAS-binding domain of the adenylate cyclase in vitro and the ability of a cAMP analogue to rescue the circadian phenotype of the mutant strain suggested that RAS2 acting via a cAMP-dependent pathway exerts metabolic control on the Neurospora circadian clock.
To further investigate the role of RAS-mediated pathways in the metabolic regulation of the clock, we also examined the circadian phenotype of a ∆rasgef strain. We found that under light-dark conditions, the phase of conidiation was delayed compared to the wt and expression of the rasgef gene was affected by glucose.
Our data indicate that RAS-mediated pathways play an important role in the metabolic compensation of the circadian clock in Neurospora crassa.
Doctoral School: Doctoral School of Molecular Medicine
Program: Cellular and Molecular Physiology
Supervisor: Krisztina Káldi
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