Green-sensitive opsin is the photoreceptor for photic entrainment of an insect circadian clock

Abstract

IntroductionEntrainment to light cycle is a prerequisite for circadian rhythms to set daily physiological events to occur at an appropriate time of day. In hemimetabolous insects, the photoreceptor molecule for photic entrainment is still unknown. Since the compound eyes are the only circadian photoreceptor in the cricket Gryllus bimaculatus, we have investigated the role of three opsin genes expressed there, opsin-Ultraviolet (opUV), opsin-Blue (opB), and opsin-Long Wave (opLW) encoding a green-sensitive opsin in photic entrainment.ResultsA daily rhythm was detected in mRNA expressions of opB and opLW but not of opUV gene. When photic entrainment of circadian locomotor rhythms was tested after injection of double-stranded RNA (dsRNA) of three opsin genes, no noticeable effects were found in opUV RNAi and opB RNAi crickets. In opLW RNAi crickets, however, some crickets lost photic entrainability and the remaining crickets re-entrained with significantly longer transient cycles to a phase-advanced light–dark cycle as compared to control crickets. Crickets often lost entrainability when treated doubly with dsRNAs of two opsin genes including opLW.ConclusionThese results show that green-sensitive OpLW is the major circadian photoreceptor molecule for photic entrainment of locomotor rhythms in the cricket G. bimaculatus. Our finding will lead to further investigation of the photic entrainment mechanism at molecular and cellular levels, which still remains largely unknown.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-015-0011-6) contains supplementary material, which is available to authorized users.

cryptochrome genes form an oscillatory loop independent of the per/tim loop in the circadian clockwork of the cricket Gryllus bimaculatus

“…Our results, however, clearly show that Gb’cry1 RNAi crickets synchronized to the given light dark cycle as robustly as the control crickets, suggesting that Gb’ CRY1 is not the major photoreceptor for entrainment of the clock. This finding is consistent with our previous reports that the compound eye is the only photoreceptor necessary for light entrainment of the cricket clock [24] and that opsin-long wavelength ( opsin-LW ) expressed in the compound eye plays a major role in photic entrainment [25]. Similarly Gb’cry2 is apparently not a major photoreceptor for entrainment, because Gb’cry2 RNAi crickets also robustly synchronized to light cycles, similar to the case for Gb’cry1 RNAi crickets.…”

“…Both Gb’cry1 and Gb’cry2 are involved in the clock machinery. The reset mechanism is exclusively relies on retinal photoreceptors [24, 25, 35]. Similarly the firebrat Thermobia domestica , one of the most primitive ametabolous insects, has a mammalian-like clock machinery in which cyc is rhythmically expressed [36, 37].…”

Light and Temperature Synchronizes Locomotor Activity in the Linden Bug, Pyrrhocoris apterus

“…When LD and TC were applied in maximal misalignment, light dominated temperature. Similarly, the dominance of light over temperature was reported for Drosophila (Yoshii et al, 2010) and for the cricket G. bimaculatus (Komada et al, 2015;Kannan et al, 2019).…”

Light input pathways to the circadian clock of insects with an emphasis on the fruit fly Drosophila melanogaster

“…As in cockroaches lesions of the compound eyes but not the ocelli impaired photoentrainment of the activity rhythms of G. bimaculatus (Tomioka and Chiba 1984;Yukizane and Tomioka 1995), suggesting that the compound eyes contain the sole photoreceptors for entraining the circadian clock. Recent studies showed that circadian entrainment is mediated by green-sensitive opsins in the compound eyes (Komada et al 2015). Their activation leads to an increase of the bZip transcription factor c-fos in the optic lobes that resets the circadian clock via CRY (Kutaragi et al 2018).…”