Journal of theoretical biologyJul 6, 2004

The natural daily rhythm of Neurospora is maintained by remaining network activity in frq gene mutants

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Updated Apr 5, 2026

Abstract

A simple model accurately reproduces the phase angle response of spore formation in arrhythmic Neurospora crassa mutants under temperature cycles.

Inactivation of the frq gene leads to arrhythmic behavior in Neurospora crassa, characterized by a lack of self-sustained oscillation.
Phase angle of spore formation in frq mutants is influenced by the period of temperature cycles.
A damped harmonic oscillator model was developed, reflecting the behavior of frq mutants and aligning with observed phase angles.
The endogenous period of 21 hours in the model corresponds to that of wild-type Neurospora, indicating a potential timekeeping role for the mutants.
The model was validated against experimental data, successfully reproducing spore formation patterns under constant conditions.

Simplified

We model theoretically the response of the widely studied circadian oscillator of Neurospora crassa to inactivation of the frq gene. The resulting organism has been termed "arrhythmic" under constant conditions. Under entrainment to periodic temperature cycles Roenneberg, Merrow and coworkers have shown that the phase angle at which spore formation occurs depends on the entrainment period, curiously even in the null frq mutants (frq9 and frq10). We show that such a response does not imply the presence of a self-sustained free-running oscillator. We derive a simple candidate model (a damped harmonic oscillator) for the null frq mutants that successfully reproduces the observed phase angle response. An endogenous period of 21 h for the damped harmonic oscillator coincides with the endogenous period of wild-type Neurospora. This suggests that the (noise driven) "residual system" present in the mutants may have a significant timekeeping role in the wild-type organism. Our model (with no change of parameters) was then used to investigate spore formation patterns under constant conditions and reproduces the corresponding experimental data of Aronson et al. (Proc. Natl. Acad. Sci. USA 91 (1994) 7683.)

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The natural daily rhythm of Neurospora is maintained by remaining network activity in frq gene mutants

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