Midnight/midday-synchronized expression of cryptochrome genes in the eyes of three teleost species, zebrafish, goldfish, and medaka

Abstract

Photoperiodic responses are observed in many organisms living in the temperate zones. The circadian clock is involved in photoperiodic time measurement; however, the underlying molecular mechanism for detection of the day length remains unknown. We previously compared the expression profiles of the Cryptochrome(Cry) genes in the zebrafish eye and reported that Cry1ab has a double peak with variable expression duration depending on the photoperiod. In this study, to understand commonalities and differences in the photoperiodic responses of ocular Cry genes, we identified Cryptochrome genes in two other teleost species, goldfish and medaka, living in temperate zones, and measured ocular Cry mRNA levels in all of the three species, under different photoperiods (long-day [14 h light: 10 h dark] and short-day [10 h light: 14 h dark] and in constant darkness. Cry1ab mRNA levels did not show dual peaks in goldfish or medaka under the examined conditions; however, the mRNA expression profiles of many Crys were altered in all three species, depending on the day length and light condition. Based on their expression profiles, Cry mRNA peaks were classified into three groups that better synchronize to sunrise (light-on), midnight/midday (middle points of the dark/light periods), or sunset (light-off). These results suggest the presence of multiple oscillators that oscillate independently or a complex oscillator in which Cry expression cycles change in a photoperiod-dependent manner in the eye.

Recent advances in biological rhythm and non-visual photoreception: Report for the session 10 at the 19th International Conference on Retinal Proteins

“…Dr. Toshiyuki Okano presented their recent studies on “Non-circadian rhythms and blue-light-dependent magnetoreception mediated by cryptochromes.” They discovered the possibility that CRY3 is involved in lunar response in a rabbitfish, which exhibits lunar phase-synchronized spawning behavior [ 6 ]. They also demonstrated, in the eyes of zebrafish, goldfish, and medaka, the existence of circadian clocks synchronized with noon (and midnight), suggesting that the clocks may be involved in the seasonal response (photoperiodism) and/or the sun compass [ 7 ]. Interestingly, recent studies including their own raises the possibility that CRY4 in the avian retina is involved in the light-dependent geomagnetoreception.…”