Complementary phase responses via functional differentiation of dual negative feedback loops.

Area of Science:

• Chronobiology
• Molecular Biology
• Systems Biology

Background:

• Mammalian circadian clocks rely on interacting negative feedback loops (NFLs) involving Period1 (Per1) and Period2 (Per2) gene expression.
• Per1 and Per2 proteins have similar functions but distinct expression peak times, suggesting differential dynamical roles.

Purpose of the Study:

• To investigate if the temporal difference in Per1 and Per2 expression peaks reflects distinct dynamical functions in the mammalian circadian clock.
• To analyze how light-induced transcription of Per1 and Per2 influences circadian clock phase responses.

Main Methods:

• Mathematical analysis of dual NFLs in the circadian clock model.
• Analysis of phase responses to light-induced transcription of Per1 and Per2 mRNAs.

Main Results:

• Light input to the earlier peaking Per1 primarily drives phase advance, while input to the later peaking Per2 drives phase delay.
• The ratio of light-induced transcription rates between Per1 and Per2 dictates the magnitude and direction of phase shifts.
• Differential induction rates explain species-specific phase response curves (e.g., rats vs. mice).

Conclusions:

• The temporal difference in Per1 and Per2 expression peaks differentiates their dynamical functions in circadian rhythm regulation.
• Complementary phase responses mediated by Per1 and Per2 contribute to the entrainability of the circadian clock to environmental light-dark cycles.