Coupling protocol of interlocked feedback oscillators in circadian clocks

Area of Science:

• Chronobiology
• Systems Biology
• Genetics

Background:

• Circadian rhythms exhibit robust oscillatory features like phase, period, and amplitude, crucial for biological timing.
• Drosophila circadian clocks rely on interlocked transcriptional-translational feedback loops for robustness.
• The evolutionary selection of specific coupling mechanisms within these feedback loops remains unclear.

Purpose of the Study:

• To investigate the mechanisms underlying the survival of specific coupling protocols in Drosophila circadian clocks.
• To compare the functional consequences of activator-coupled oscillators (ACO) versus repressor-coupled oscillators (RCO).
• To determine the relative importance of cycle phase, robustness, and entrainability in evolved circadian systems.

Main Methods:

• Comparative analysis of two distinct coupling protocols: ACO and RCO.
• Focus on coupling parameters: dissociation constant and time-delay.
• Utilized deterministic and stochastic analyses to assess cycle properties and parameter sensitivity.

Main Results:

• ACO generated anti-phase (morning-evening) cycles, while RCO produced in-phase cycles.
• Anti-phase ACO exhibited greater amplitude fluctuations under parameter variations and perturbations compared to in-phase RCO.
• ACO impaired entrainability to the day-night cycle, whereas RCO demonstrated high entrainability.

Conclusions:

• The evolved ACO mechanism, producing anti-phase cycles, suggests this pattern is more critical for Drosophila than robustness or entrainability.
• This finding offers a novel hypothesis for the evolutionary significance of specific circadian clock architectures.
• The study highlights trade-offs between different functional properties in biological oscillator systems.