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Updated: Jun 26, 2026
In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters
Published on: July 4, 2018
Unusual circadian locomotor activity and pathophysiology in mutant CRY1 transgenic mice
Satoshi Okano1, Makoto Akashi, Kiyoshi Hayasaka
1Research Laboratory for Molecular Genetics, Yamagata University, Yamagata 990-9585, Japan. sikano@med.id.yamagata-u.ac.jp
Abstract:
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 28h) 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.
Insights
A specific CRY1 protein motif is crucial for mammalian circadian rhythms and overall physiology. Mutations disrupt daily rhythms and lead to diabetes-like symptoms in mice.
Area of Science:
- Chronobiology
- Molecular Biology
- Genetics
Background:
- Mammalian circadian rhythms rely on cryptochrome proteins (CRYs) as inhibitors in the CLOCK-BMAL1 feedback loop.
- Understanding the in vivo function of mammalian CRYs is essential for deciphering circadian regulation.
Purpose of the Study:
- To investigate the role of a conserved CRY1 dipeptide motif in mammalian circadian rhythm and physiology.
- To analyze the effects of a specific CRY1 mutation (CRY1-AP) on circadian behavior and metabolic health.
Main Methods:
- Generation of transgenic mice overexpressing wild-type CRY1 (CRY1 Tg) and a mutated CRY1 (CRY1-AP Tg).
- Observation and analysis of locomotor activity patterns, circadian periods, and entrainment in constant darkness and light-dark cycles.
- Assessment of physiological symptoms, including those characteristic of diabetes mellitus.
Main Results:
- CRY1 Tg mice exhibited robust circadian rhythms.
- CRY1-AP Tg mice displayed significantly prolonged free-running periods (around 28 hours) and rhythm splitting.
- CRY1-AP Tg mice showed abnormal light-dark cycle entrainment and developed diabetes mellitus-like symptoms.
Conclusions:
- The conserved dipeptide motif in CRY1 is critical for the mammalian clock system.
- Disruption of this motif severely impacts circadian rhythmicity and physiological homeostasis, leading to metabolic dysfunction.
