THE MECHANISM OF EXPRESSION OF CIRCADIAN CLOCK RELATED PROTEINS IN AN INSECT OPTIC LOBE

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We investigated the mechanism of expression of clock related proteins in the optic lobe of the cricket Gryllus bimaculatus. 1) The effects of a translation inhibitor, cycloheximide (CHX), on the circadian neuronal activity rhythm of the optic lamina-medulla compound eye complex cultured in vitro were examined. Continuous application of CHX abolished circadian rhythms of both the spontaneous neuronal activity and the visually evoked response. However, it abolished neither the spontaneous activity nor the visually evoked response. 2) When the complex was treated with 10^<-5> M CHX for 6 h, the rhythm exhibited a marked phase shift. The magnitude and direction of the phase shift were dependent on the phase at which the complex was treated with CHX ; phase delays occurred during the late subjective day to early subjective night, whereas phase advances occurred around the late subjective night. 3) The phase response curve for a reversible transcription inhibitor, 5,6-dichlorobenzimidazole riboside (DRB), shows both phase delay and advance 6hrs earlier than that for CHX.4) The abundance of 31kDa protein, which shows a circadian rhythm in its abundance, was reduced when the rhythm was shifted by CHX or DRB.5) PDF and PERIOD, which are involved in the circadian rhythm in Drosophila, also showed circadian rhythmic change in their abundance in the optic lobe. 6) Immunohistochemistry revealed that PERIOD protein is expressed in cells located in the outer chiasma between the lamina and the medulla. These results suggest that gene expression including transcription and translation is a required process in the cricket optic lobe circadian clock, and that PDF and PERIOD may be involved in the clock mechanism.