Pigment-Dispersing Factor Affects Nocturnal Activity Rhythms, Photic Entrainment, and the Free-Running Period of the Circadian Clock in the Cricket Gryllus bimaculatus

Abstract

Pigment-dispersing factor (PDF) is a neuropeptide widely distributed in insect brains and plays important roles in the circadian system. In this study, we used RNA interference to study the role of the pigment-dispersing factor (pdf) gene in regulating circadian locomotor rhythms in the cricket, Gryllus bimaculatus. Injections of pdf double-stranded RNA (dspdf) effectively knocked down the pdf mRNA and PDF peptide levels. The treated crickets maintained the rhythm both under light-dark cycles (LD) and constant darkness (DD). However, they showed rhythms with reduced nocturnal activity with prominent peaks at lights-on and lights-off. Entrainability of dspdf-injected crickets was higher than control crickets as they required fewer cycles to resynchronize to the LD cycles shifted by 6 h. The free-running periods of the dspdf-injected crickets were shorter than those of control crickets in DD. These results suggest that PDF is not essential for the rhythm generation but involved in control of the nocturnality, photic entrainment, and fine tuning of the free-running period of the circadian clock.

The involvement of the brain region containing pigment-dispersing factor-immunoreactive neurons in the photoperiodic response of the bean bugRiptortus pedestris

“…Moreover, pdf mRNA expression levels showed no diurnal rhythmicity under either long or short days in the head of R. pedestris. Although diurnal and circadian expression of pdf mRNA were reported for A. mellifera (Sumiyoshi et al, 2011), pdf mRNA levels and cytoplasmic PDF immunoreactivity showed no prominent oscillation in many other insects (Park and Hall, 1998;Park et al, 2000;Matsushima et al, 2003;Hassaneen et al, 2011). However, circadian oscillations of immunoreactivity have been reported in the terminals of s-LN v s in D. melanogaster (Park et al, 2000).…”

“…In G. bimaculatus, the decrease of PDF immunoreactivity by RNAi was much slower than that of pdf mRNA levels, and complete disappearance was not observed during the 20 days after dsRNA injection, although pdf RNAi decreased PDF immunoreactivity to below the detection limit within 10 days in B. germanica (Lee et al, 2009;Hassaneen et al, 2011). The long lifetime of the PDF peptide would explain the high PDF immunoreactivity in the fibres of PDFMe neurons, even 20 days after the cell bodies were completely removed.…”

“…Despite these decreases of mRNA and peptide levels, however, no effects of pdf RNAi on the photoperiodic response of R. pedestris were observed. It is still possible that a small amount of PDF peptides remaining in the cell bodies or fibres was sufficient for the photoperiodic response in R. pedestris; however, even a slight decrease of PDF peptides affected the locomotor activity rhythm in G. bimaculatus (Hassaneen et al, 2011). Therefore, it is most likely that the PDF peptide itself or at least pdf mRNA expression is not involved or plays a negligible role in the photoperiodic response in R. pedestris.…”

“…Using RNA interference (RNAi) techniques, it was shown that knockdown of pdf gene expression disrupted the circadian locomotor rhythm of the German cockroach, Blattella germanica (Lee et al, 2009). pdf RNAi was also applied to G. bimaculatus and resulted in suppression of nocturnal activity, shortening of the freeInvolvement of the brain region containing pigment-dispersing factor-immunoreactive neurons in the photoperiodic response of the bean bug, Riptortus pedestris running period in constant darkness, and enhancement of the photic entrainability to shifted light-dark cycles (Hassaneen et al, 2011).…”

Post-Embryonic Development of Circadian Oscillations Within and Outside the Optic Lobe in the Cricket,Gryllus bimaculatus

“…The output pathway controlling overt rhythms also remains to be explicated. Cerebral PDF neurons are apparently involved in the clock's output pathway, because RNAi of pdf gene reduced the nocturnal activity with reduced amount of PDF (Hassaneen et al, 2011). PDF is more strongly involved in control of overt activity rhythms in Drosophila and cockroaches.…”