Effects of cryptochrome-modulating compounds on circadian behavioural rhythms in zebrafish

The circadian clock controls daily rhythms of various physiological processes, and impairment of its function causes many diseases including sleep disorders. Chemical compounds that regulate clock function are expected to be applied for treatment of circadian clock-related diseases. We previously identified small-molecule compounds KL001, KL101 and TH301 that lengthen the period of cellular circadian clock by directly targeting clock proteins cryptochromes (CRYs) in mammals. KL001 targets both CRY1 and CRY2 isoforms, while KL101 and TH301 are isoform-selective compounds and require CRY C-terminal region for their effects. For further application of these compounds, the effects on locomotor activity rhythms at the organismal level need to be investigated. Here we used zebrafish larvae as an in vivo model system and found that KL001 lengthened the period of locomotor activity rhythms in a dose-dependent manner. In contrast, KL101 and TH301 showed no effect on the period. The amino acid sequences of CRY C-terminal regions are diverged in zebrafish and mammals, supporting the importance of this region for the effects of KL101 and TH301. This study demonstrated efficacy of CRY modulation for controlling circadian behavioural rhythms in organisms and suggested species-dependent differences in the effects of isoform-selective CRY-modulating compounds.