The mouse Clock mutation lowers the strength of daily rhythms and increases how strongly timing cues reset them

Heterozygous Clock/+ mice show high-amplitude phase-resetting responses to light compared to wild-type mice.

• Clock/+ mice exhibit Type 0 phase-resetting responses, while wild-type mice display Type 1 responses.
• The mutation does not affect the acute light induction of Per1 and Per2 genes in the suprachiasmatic nuclei.
• Circadian rhythms of Per gene expression are significantly reduced in both Clock homozygous and heterozygous mutants.
• PER2::LUCIFERASE expression in explant cultures from Clock heterozygotes shows reduced amplitude.
• Phase-response curves to changes in culture medium are Type 0 for Clock heterozygotes and Type 1 for wild types.
• A model suggests that the Clock mutation reduces the amplitude of the circadian pacemaker in the suprachiasmatic nuclei.

Simplified