Functional analysis of Pdp1 and vrille in the circadian system of a cricket

Abstract

Circadian rhythms are generated by a circadian clock for which oscillations are based on the rhythmic expression of the so-called clock genes. The present study investigated the role of Gryllus bimaculatus vrille (Gb’vri) and Par domain protein 1 (Gb’Pdp1) in the circadian clock of the cricket Gryllus bimaculatus. Structural analysis of Gb’vri and Gb’Pdp1 cDNAs revealed that they are a member of the bZIP transcription factors. Under light/dark cycles (LD) both genes were rhythmically expressed in the clock tissue, the optic lobes, whereas the rhythm diminished under constant darkness (DD). Gb’vri and Gb’Pdp1 mRNA levels were significantly reduced by RNA interference (RNAi) of Gb’Clk and Gb’cyc, suggesting they are controlled by Gb’CLK/Gb’CYC. RNAi of Gb’vri and Gb’Pdp1 had little effect on locomotor rhythms, although their effects became visible when treated together with Gb’cycRNAi. The average free-running period of Gb’vriRNAi/Gb’cycRNAi crickets was significantly shorter than that of Gb’cycRNAi crickets. A similar period shortening was observed also when treated with Gb’Pdp1RNAi/Gb’cycRNAi. Some Gb’Pdp1RNAi/Gb’cycRNAi crickets showed rhythm splitting into two free-running components with different periods. Gb’vriRNAi and Gb’Pdp1RNAi treatments significantly altered the expression of Gb’Clk, Gb’cyc, and Gb’tim in LD. These results suggest that Gb’vri and Gb’Pdp1 play important roles in cricket circadian clocks.