Unusual circadian locomotor activity and pathophysiology in mutant CRY1 transgenic mice

In the widely accepted molecular model underlying mammalian circadian rhythm, cryptochrome proteins (CRYs) play indispensable roles as inhibitive components of the CLOCK-BMAL1-mediated transcriptional-translational negative feedback loop. In order to clarify yet uncovered aspects of mammalian CRYs in vivo, we generated transgenic (Tg) mice ubiquitously overexpressing CRY1 as well as CRY1 having a mutation in the dipeptide motif of cysteine and proline that is conserved beyond evolutional divergence among animal CRYs: cysteine414 of the motif was replaced with alanine (CRY1-AP). The mice overexpressing CRY1 (CRY1 Tg) exhibited robust circadian rhythms of locomotor activity. In sharp contrast, the mice overexpressing CRY1-AP (CRY1-AP Tg) displayed a unique circadian phenotype. Their locomotor free-running periods were very long (around 28 h) with rhythm splitting: the bout of activity of CRY1-AP Tg mice was split into two equal components in constant darkness. Moreover, CRY1-AP Tg mice displayed abnormal entrainment behavior: their bout of activity shifted immediately in response to a shift of the light–dark cycles. In addition, we found that CRY1-AP Tg mice showed symptoms characteristic of diabetes mellitus. The results indicate that the motif of CRY1 is crucial to the mammalian clock system and physiology.