How the Clock Protein Affects the Flexibility of the Body’s Daily Rhythm Adjustment

Wild-type mice can only synchronize to a light-dark cycle of 24 hours, while Clock mutant mice can adapt to cycles of 24, 28, and 32 hours.

• Circadian rhythms in wild-type mice are limited to a 24-hour light-dark cycle.
• Clock mutant mice can synchronize to longer cycles of 28 and 32 hours but fail to entrain to 20-hour and 36-hour cycles.
• Under a 28-hour light-dark cycle, Clock mutant mice exhibited rhythmic expression of Per2 mRNA in the suprachiasmatic nucleus.
• Increased light response was observed in Clock mutant mice compared to wild-type.
• The findings suggest the clock gene may influence the limits of circadian entrainment in the suprachiasmatic nucleus.

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