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

Animals exhibit circadian rhythms with a period of approximately 24 h in various physiological functions, including locomotor activity. This rhythm is controlled by an endogenous oscillatory mechanism, or circadian clock, which consists of cyclically expressed clock genes and their product proteins. ( ) genes are thought to be involved in the clock mechanism, and their functions have been examined extensively in holometabolous insects, but in hemimetabolous insects their role is less well understood. In the present study, the role of genes was investigated using RNAi technology in a hemimetabolous insect, the cricket . Using a molecular cloning approach, we obtained cDNAs for two genes: -type ( ) and mammalian-type ( ). has six splicing variants, most of which showed rhythmic mRNA expression. treatment had only a limited effect at the behavioral and molecular levels, while had a significant effect on behavioral rhythms and molecular oscillatory machinery, alone or in combination with . In / double-RNAi crickets, most clock genes showed arrhythmic expression, except for , which retained clear rhythmic expression. Molecular analysis revealed that some combination of and variants suppressed CLK/CYC transcriptional activity in cultured cells. Based on these results, we propose a new model of the cricket's circadian clock, including a molecular oscillatory loop for , which can operate independent of the / loop.