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

Abstract

The concept of insect photoperiodism based on a circadian clock has been supported by many studies demonstrating that the behavioural circadian rhythm and the photoperiodic response are driven by the same circadian clock genes. However, the neuronal mechanism of the circadian clock underlying photoperiodism is poorly understood. To examine whether circadian rhythm and photoperiodism share a neuronal mechanism, we focused on the neurons that express neuropeptide pigment-dispersing factor (PDF) in the bean bug, Riptortus pedestris. PDF has been identified as an important regulator of the insect circadian rhythm and is expressed in circadian clock neurons of various insect species. In R. pedestris, PDF immunoreactivity was detected in some clusters of cells and their fibres in the optic lobe and the protocerebrum. cDNA encoding a PDF precursor protein was highly conserved between R. pedestris and many other insects. Differences between day and night were not observed in the immunolabelling intensity in cell bodies of PDFimmunoreactive neurons and pdf mRNA expression levels in the head. Surgical removal of the region containing PDF-immunoreactive cell bodies at the medulla disrupted the photoperiodic regulation of diapause. However, gene suppression of pdf by RNA interference did not affect the photoperiodic response. These results suggest that the region containing PDF-immunoreactive somata is important for the photoperiodic response in R. pedestris, but pdf mRNA expression is probably not required for the response.

Functional circadian clock genes are essential for the overwintering diapause of the Northern house mosquito,Culex pipiens

“…In a recent study, Ikeno et al (Ikeno et al, 2014) investigated the role of pdf on diapause initiation in R. pedestris. Surprisingly, pdf mRNA did not affect diapause initiation in bean bugs as knocking down pdf with RNAi did not affect the reproductive status of long day-or short day-reared bugs.…”

Evolution of pigment‐dispersing factor neuropeptides in panarthropoda: Insights from onychophora (velvet worms) and tardigrada (water bears)

“…This contrasts with the situation in insects and crustaceans, in which clusters of PDF-ir neurons are clearly associated with the optic lobes of the compound eyes. Most insects have three or four groups of PDF-ir somata associated with the medulla and lamina of their optic lobes (see, e.g., Helfrich-F€ orster, 1995Helfrich-F€ orster, , 1997Helfrich-F€ orster et al, 1998;Homberg et al, 1991;Honda et al, 2006;Ikeno et al, 2014;N€ assel et al, 1991Reischig and Stengl, 2003;Sato et al, 2002;Sehadov a et al, 2003;Wei et al, 2010;Wen and Lee, 2008), and similar PDH-ir cell clusters are associated with the medulla and lamina in crustaceans (Harzsch et al, 2009;Hsu et al, 2008;Mangerich et al, 1987;Nussbaum and Dircksen, 1995;Strauß et al, 2011). Notably, and in contrast to the optic lobes of the compound eyes, PDF-ir somata are not associated with the median ocelli of insects or the nauplius eyes of crustaceans (see, e.g., Reischig and Stengl, 2003;Sousa et al, 2008;Strauß et al, 2011;Wei et al, 2010).…”

Genomic basis of circannual rhythm in the european corn borer moth

“…In addition to interaction of per and Pdfr 301 in pacemaker neurons, a second route for epistasis and control of termination could occur by the release of ecdysone through an independent Pdfr cascade in the PG discovered in the silkmoth Bombyx mori (Figure 303 7) (84). Indeed, knockdowns of Pdf are sufficient to induce diapause under long photoperiods in mosquitos 304 (Culex pipiens) and ablation of PDF-positive neurons impairs the photoperiodic regulation of diapause in 305 bean bugs (Riptortus pedestris) and blow flies (Protophormia terraenovae)(63,85,86).…”