Molecular approach to the circadian clock mechanism in the cricket

Circadian rhythms are physiological and behavioral changes that follow a roughly 24-h period, responding primarily to daily cycles in an organism’s environment. Crickets have provided a good model to study the neural mechanisms controlling the circadian rhythm, because they have a large central nervous system. Neurobiological studies revealed that the circadian clock is located in the optic lobe and the photoreceptors necessary for light entrainment are in the compound eye. Recent progress in molecular technology enabled us to use crickets for dissection of the circadian system at a molecular level. The oscillatory mechanism of the circadian clock has been studied in Drosophila and a few higher order insect species, but the results from those insects are often inconsistent. We employed a reverse genetic approach to the cricket clock. We first obtained clock genes, period (per), timeless (tim), and Clock (Clk) with molecular cloning and then analyzed their functions with RNAi technology. The obtained results could be only partially explained by the Drosophila model. The central oscillatory mechanism of the cricket clock will be discussed together with the peripheral oscillators and the involvement of pigment-dispersing factor as a neurotransmitter in regulating the locomotor rhythm.