A model for generating circadian rhythm by coupling ultradian oscillators
Date
2006-02-23
Authors
Paetkau, Verner
Edwards, Roderick
Illner, Reinhard
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Organisms ranging from humans to cyanobacteria undergo circadian rhythm, that
is, variations in behavior that cycle over a period about 24 hours in length. A fundamental property
of circadian rhythm is that it is free-running, and continues with a period close to 24 hours in the
absence of light cycles or other external cues. Regulatory networks involving feedback inhibition
and feedforward stimulation of mRNA transcription and translation are thought to be critical for
many circadian mechanisms, and genes coding for essential components of circadian rhythm have
been identified in several organisms. However, it is not clear how such components are organized
to generate a circadian oscillation.
Results: We propose a model in which two independent transcriptional-translational oscillators
with periods much shorter than 24 hours are coupled to drive a forced oscillator that has a
circadian period, using mechanisms and parameters of conventional molecular biology.
Furthermore, the resulting circadian oscillator can be entrained by an external light-dark cycle
through known mechanisms. We rationalize the mathematical basis for the observed behavior of
the model, and show that the behavior is not dependent on the details of the component ultradian
oscillators but occurs even if quite generalized basic oscillators are used.
Conclusion: We conclude that coupled, independent, transcriptional-translational oscillators with
relatively short periods can be the basis for circadian oscillators. The resulting circadian oscillator
can be entrained by 24-hour light-dark cycles, and the model suggests a mechanism for its
evolution.
Description
BioMed Central
Keywords
Citation
Paetkau et al. A model for generating circadian rhythm by coupling ultradian oscillators. Theoretical Biology and Medical Modelling 2006, 3 :12