Isochron-based phase response analysis of circadian rhythms

Area of Science:

• Chronobiology
• Systems Biology
• Mathematical Modeling

Background:

• Circadian rhythms are endogenous biological processes synchronized with environmental cycles, primarily light.
• Entrainment of circadian rhythms relies on the phase synchronization of gene regulation to external cues.
• Understanding circadian phase behavior is crucial for elucidating the mechanisms of circadian entrainment.

Purpose of the Study:

• To present novel phase analyses for oscillatory systems to understand circadian rhythm dynamics.
• To compute the phase response curve (PRC) of circadian rhythms using these analytical methods.
• To apply these analyses to a Drosophila circadian rhythm model, generating testable hypotheses.

Main Methods:

• Developed two phase analyses for oscillatory systems, applicable to infinitesimal and finite perturbations.
• Utilized isochrons as a phase metric to characterize the limit cycle behavior of circadian rhythms.
• Applied the developed methods to a mechanistic model of the Drosophila circadian clock.

Main Results:

• The phase analyses provide a framework for calculating the phase response curve of circadian rhythms.
• Application to the Drosophila model yielded experimentally testable hypotheses regarding circadian phase control.
• Demonstrated the significance of phase and period modulations in the process of circadian photic entrainment.

Conclusions:

• The presented phase analysis methods offer a robust approach to studying circadian rhythm entrainment.
• The findings provide insights into the molecular mechanisms governing circadian responses to light.
• This work supports the critical role of dynamic phase and period adjustments in aligning internal clocks with external light cycles.