Vrille is required for larval moulting and metamorphosis of Helicoverpa armigera (Lepidoptera: Noctuidae)

Molecular Oscillator Affects Susceptibility of Caterpillars to Insecticides: Studies on the Egyptian Cotton Leaf Worm-Spodoptera littoralis (Lepidoptera: Noctuidae)

The molecular oscillator is the core of the biological clock and is formed by genes and proteins whose cyclic expression is regulated in the transcriptional-translational feedback loops (TTFLs). Proteins of the TTFLs are regulators of both their own and executive genes involved in the control of many processes in insects (e.g., rhythmic metabolism of xenobiotics, including insecticides). We disrupted the clock operation in S. littoralis larvae by injecting the dsRNA of clock genes into their body cavity and culturing the larvae under continuous light. As a result, the daily susceptibility of larvae to insecticides was abolished and the susceptibility itself increased (in most cases). In the fat body, midgut, and Malpighian tubules (the main organs metabolizing xenobiotics) of the larvae treated with injected-dsRNA, the daily activity profiles of enzymes involved in detoxification-cytochrome P450 monooxygenases, Glutathione-S-transferase, and esterase-have changed significantly. The presented results prove the role of the molecular oscillator in the regulation of larvae responses to insecticides and provide grounds for rational use of these compounds (at suitable times of the day), and may indicate clock genes as potential targets of molecular manipulation to produce plant protection compounds based on the RNAi method.

Novel mechanisms of epithelial ion transport: insights from the cryptonephridial system of lepidopteran larvae

Lepidopterans are among the most widespread and easily recognized insects. Whereas adult lepidopterans are known for their beauty and ecological importance as pollinators and sources of food for other animals, larvae are economically important pests of forests and agricultural crops. In the larval body, rapid growth while feeding on plant-based diet is associated with extreme alkalinity (up to pH = 11) of the midgut lumen that helps digest plant proteins. Additionally, the presence of plant secondary metabolites which serve as anti-herbivory agents requires uninterrupted excretory function, accomplished primarily by the Malpighian tubules (MTs). The so-called cryptonephridial condition, along with extreme regional heterogeneity of the MTs, and the ability to rapidly and reversibly alter the direction of epithelial ion transport are features that allow uninterrupted MT functioning and recycling of base equivalents. Studies of MTs in lepidopteran larvae have revealed that rapid adjustments in epithelial ion transport include unexpected roles for voltage-gated, ligand-gated and mechanosensitive ion channels, as well as gap junctions. These molecular components are present in epithelia of a variety of vertebrates and invertebrates and thus are likely to constitute a universal epithelial toolkit for rapid autonomous regulation of epithelial function.

VRILLE shows high divergence among Higher Diptera flies but may retain role as transcriptional repressor of clock

In the circadian system, the clock gene vrille (vri) is an essential component of the second feedback loop, being responsible in Drosophila for the rhythmicity of the Clock (Clk) gene transcription by its repression. Here we studied vri in a fruit fly pest, the Tephritidae Anastrepha fraterculus, aimingtoinvestigate its molecular evolution and expression patterns from whole-head extracts. We used a combination of transcriptomic, genomic and gene walking strategies to sequence and characterize Afravri in male and female head transcriptomes of A. fraterculus and detected two putative isoforms that may correspond to A and D vri isoforms of Drosophila. Both isoforms produced a full-length sequence that translates to 842 amino acids. While the protein sequence showed significant divergence to orthologous sequences from other organisms, the bZIP domain was highly conserved. Molecular evolutionary analyses showed that vri in higher Diptera flies has been evolving under positive selection. A more detailed analysis showed positive selection also in Tephritidae with 29 sites evolving under positive selection in comparison with Drosophilidae. Real time expression analysis in LD and DD conditions showed cyclic expression of Afravri mRNA with oscillation opposite to AfraClk, suggesting that VRI may also behave in Anastrepha as a transcriptional repressor of Clk, providing another indication that higher Diptera might share common interlocked transcript-translation feedback loops (TTFLs) mechanisms that differ from other insects in target genes.

The role of clockwork orange in the circadian clock of the cricket Gryllus bimaculatus

The circadian clock generates rhythms of approximately 24 h through periodic expression of the clock genes. In insects, the major clock genes period (per) and timeless (tim) are rhythmically expressed upon their transactivation by CLOCK/CYCLE, with peak levels in the early night. In Drosophila, clockwork orange (cwo) is known to inhibit the transcription of per and tim during the daytime to enhance the amplitude of the rhythm, but its function in other insects is largely unknown. In this study, we investigated the role of cwo in the clock mechanism of the cricket Gryllus bimaculatus. The results of quantitative RT-PCR showed that under a light/dark (LD) cycle, cwo is rhythmically expressed in the optic lobe (lamina-medulla complex) and peaks during the night. When cwo was knocked down via RNA interference (RNAi), some crickets lost their locomotor rhythm, while others maintained a rhythm but exhibited a longer free-running period under constant darkness (DD). In cwo^RNAi crickets, all clock genes except for cryptochrome 2 (cry2) showed arrhythmic expression under DD; under LD, some of the clock genes showed higher mRNA levels, and tim showed rhythmic expression with a delayed phase. Based on these results, we propose that cwo plays an important role in the cricket circadian clock.

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

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'cyc^RNAi. The average free-running period of Gb'vri^RNAi/Gb'cyc^RNAi crickets was significantly shorter than that of Gb'cyc^RNAi crickets. A similar period shortening was observed also when treated with Gb'Pdp1^RNAi/Gb'cyc^RNAi. Some Gb'Pdp1^RNAi/Gb'cyc^RNAi crickets showed rhythm splitting into two free-running components with different periods. Gb'vri^RNAi and Gb'Pdp1^RNAi 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.