The clock genes period 1 and period 2 mediate diurnal rhythms in dioxin-induced Cyp1A1 expression in the mouse mammary gland and liver

Treatment with TCDD induced Cyp1A1 expression 23-43-fold more during the night than during the daytime in wild type mice.

• Transcription factors with PAS domains are crucial for the mammalian circadian clock and may influence toxin responses.
• The expression of Cyp1A1, a target of AhR signaling, was significantly higher at night compared to daytime in the mammary gland and liver.
• Diurnal variation in Cyp1A1 expression in response to TCDD was lost in mutant mice lacking Per1 and Per2.
• These findings suggest that Per1 and Per2 play a role in regulating the timing of AhR responses to toxins.

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