Pigment-dispersing factor affects circadian molecular oscillations in the cricket Gryllus bimaculatus

Pigment-dispersing factor (PDF) is an important neurotransmitter in insect circadian systems. In the cricket Gryllus bimaculatus, it affects nocturnal activity, the free-running period and photic entrainment. In this study, to investigate whether these effects of PDF occur through a circadian molecular machinery, we measured mRNA levels of clock genes period (per) and timeless (tim) in crickets with pdf expression knocked-down by pdf RNAi. The pdf RNAi decreased per and tim mRNA levels during the night to reduce the amplitude of their oscillation. The phase of the rhythm advanced by about 4h in terms of trough and/or peak phases. On the other hand, pdf mRNA levels were little affected by per and tim RNAi treatment. These results suggest that PDF affects the circadian rhythm at least in part through the circadian molecular oscillation while the circadian clock has little effect on the pdf expression.