Reciprocal Coupling of Circadian Clocks in the Compound Eye and Optic Lobe in the Cricket Gryllus bimaculatus

The circadian system comprises multiple clocks, including central and peripheral clocks. The central clock generally governs peripheral clocks to synchronize circadian rhythms throughout the animal body. However, whether the peripheral clock influences the central clock is unclear. This issue can be addressed through a system comprising a peripheral clock (compound eye clock [CE clock]) and central clock (the optic lobe [OL] clock) in the cricket Gryllus bimaculatus. We previously found that the compound eye regulates the free-running period (tau) and the stability of locomotor rhythms driven by the OL clock, as measured by the daily deviation of tau at 30 degrees C. However, the role of the CE clock in this regulation remains unexplored. In this study, we investigated the importance of the CE clock in this regulation using RNA interference (RNAi) of the period (per) gene localized to the compound eye (per(CE-RNAi)). The per(CE-RNAi) abolished the compound eye rhythms of the electroretinogram (ERG) amplitude and clock gene expression but the locomotor rhythm driven by the OL clock was maintained. The locomotor rhythm of the tested crickets showed a significantly longer tau and greater daily variation of tau than those of control crickets treated with dsDsRed2. The variation of tau was comparable with that of crickets with the optic nerve severed. The tau was considerably longer but was comparable with that of crickets with the optic nerve severed. These results suggest that the CE clock regulates the OL clock to maintain and stabilize tau.