title: Green-sensitive opsin is the photoreceptor for photic entrainment of an insect circadian clock.
abstract: BACKGROUND
  Entrainment 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.
  
  
  RESULTS
  A 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.
  
  
  CONCLUSIONS
  These 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.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Komada
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kamae
authors.affiliation: Graduate School of Science, Osaka City University, Osaka, 558-8585 Japan.
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Koyanagi
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Kousuke
authors.initials: K
authors.lastname: Tatewaki
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Ehab
authors.initials: E
authors.lastname: Hassaneen
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan ; Bangladesh Atomic Energy Commission, Dhaka, 1212 Bangladesh.
authors.forename: Asm
authors.initials: A
authors.lastname: Saifullah
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Taishi
authors.initials: T
authors.lastname: Yoshii
authors.affiliation: Graduate School of Science, Osaka City University, Osaka, 558-8585 Japan.
authors.forename: Akihisa
authors.initials: A
authors.lastname: Terakita
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Tomioka
keywords: Circadian clock; Compound eye; Cricket; Entrainment; Opsin; RNAi