A novel photic entrainment mechanism for the circadian clock in an insect: involvement of c-fos and cryptochromes

Yuki Kutaragi,Yoshiyuki Moriyama,Atsushi Tokuoka,Motoki Nose,Yasuaki Tomiyama,Kenji Tomioka,Tetsuya Bando,Takayuki Watanabe

doi:10.1186/s40851-018-0109-8

Yuki Kutaragi, Yoshiyuki Moriyama + Show 6 more

Open Access

https://doi.org/10.1186/s40851-018-0109-8

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Abstract

Background Entrainment to the environmental light cycle is an essential property of the circadian clock. Although the compound eye is known to be the major photoreceptor necessary for entrainment in many insects, the molecular mechanisms of photic entrainment remain to be explored. ResultsWe found that cryptochromes (crys) and c-fos mediate photic entrainment of the circadian clock in a hemimetabolous insect, the cricket Gryllus bimaculatus. We examined the effects of RNA interference (RNAi)-mediated knockdown of the cry genes, Gb’cry1 and Gb’cry2, on photic entrainment, and light-induced resetting of the circadian locomotor rhythm. Gb’cry2 RNAi accelerated entrainment for delay shifts, while Gb’cry1/ Gb’cry2 double RNAi resulted in significant lengthening of transient cycles in both advance and delay shifts, and even in entrainment failure in some crickets. Double RNAi also strongly suppressed light induced resetting. The Gb’cry-mediated phase shift or resetting of the rhythm was preceded by light-induced Gb’c-fosB expression. We also found that Gb’c-fosB, Gb’cry2 and Gb’period (Gb’per) were likely co-expressed in some optic lobe neurons.ConclusionBased on these results, we propose a novel model for photic entrainment of the insect circadian clock, which relies on the light information perceived by the compound eye.

Highlights

Entrainment to the environmental light cycle is an essential property of the circadian clock
We investigated the role of cry1 and cry2 genes in photic entrainment of the circadian clock in the cricket, Gryllus bimaculatus
We propose a novel model of photic entrainment of the insect circadian clock, which furthers our understanding of the insect circadian system

Summary

Introduction

Entrainment to the environmental light cycle is an essential property of the circadian clock. It is generally thought that the products of Clk and cyc genes heterodimerize to form a CLOCK (CLK)/CYCLE (CYC) complex, which activates transcription of per and tim in the late day to early night, and PERIOD (PER) and TIMELESS (TIM) proteins form a heterodimer that inhibits CLK/CYC transcriptional activity later at night [2, 3] An essential property of the clock is the ability to synchronize with daily environmental cycles, with sunlight as the most important time cue The mechanism for this synchronization, or entrainment, is best understood in Drosophila, which uses CRYPTOCHROME (dCRY or CRY1) as a photoreceptor molecule.

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