Modulation of insect Cav channels by peptidic spider toxins

Insects have a much smaller repertoire of voltage-gated calcium (Ca-v) channels than vertebrates. Drosophila melanogaster harbors only a single ortholog of each of the vertebrate Ca(v)1, Ca(v)2, and Ca(v)3 subtypes, although its basal inventory is expanded by alternative splicing and editing of Ca-v channel transcripts. Nevertheless, there appears to be little functional plasticity within this limited panel of insect Ca-v channels, since severe loss-of-function mutations in genes encoding the pore-forming a, subunits in Drosophila are embryonic lethal. Since the primary role of spider venom is to paralyze or kill insect prey, it is not surprising that most, if not all, spider venoms contain peptides that potently modify the activity of these functionally critical insect Ca-v channels. Unfortunately, it has proven difficult to determine the precise ion channel subtypes recognized by these peptide toxins since insect Ca-v channels have significantly different pharmacology to their vertebrate counterparts, and cloned insect Ca-v channels are not available for electrophysiological studies. However, biochemical and genetic studies indicate that some of these spider toxins might ultimately become the defining pharmacology for certain subtypes of insect Ca-v channels. This review focuses on peptidic spider toxins that specifically target insect Ca-v channels. In addition to providing novel molecular tools for ion channel characterization, some of these toxins are being used as leads to develop new methods for controlling insect pests. (c) 2006 Elsevier Ltd. All rights reserved.

Wolbachia-induced cytoplasmic incompatibility as a means for insect pest population control

Biological control is the purposeful introduction of parasites, predators, and pathogens to reduce or suppress pest populations. Wolbachia are inherited bacteria of arthropods that have recently attracted attention for their potential as new biocontrol agents. Wolbachia manipulate host reproduction by using several strategies, one of which is cytoplasmic incompatibility (CI) [Stouthamer, R., Breeuwer, J. A. J. & Hurst, G. D. D. (1999) Annu. Rev. Microbiol. 53,71-102]. We established Wolbachia-infected lines of the medfly Ceratitis capitata using the infected cherry fruit fly Rhagoletis cerasi as donor. Wolbachia induced complete CI in the novel host. Laboratory cage populations were completely suppressed by single releases of infected males, suggesting that Wolbachia-induced CI could be used as a novel environmentally friendly tool for the control of medfly populations. The results also encourage the introduction of Wolbachia into pest and vector species of economic and hygenic relevance to suppress or modify natural populations.

Ultraconserved elements in insect genomes: A highly conserved intronic sequence implicated in the control of homothorax mRNA splicing

Recently, we identified a large number of ultraconserved (uc) sequences in noncoding regions of human, mouse, and rat genomes that appear to be essential for vertebrate and amniote ontogeny. Here, we used similar methods to identify ultraconserved genomic regions between the insect species Drosophila melanogaster and Drosophila pseudoobscura, as well as the more distantly related Anopheles gambiae. As with vertebrates, ultraconserved sequences in insects appear to Occur primarily in intergenic and intronic sequences, and at intron-exon junctions. The sequences are significantly associated with genes encoding developmental regulators and transcription factors, but are less frequent and are smaller in size than in vertebrates. The longest identical, nongapped orthologous match between the three genomes was found within the homothorax (hth) gene. This sequence spans an internal exon-intron junction, with the majority located within the intron, and is predicted to form a highly stable stem-loop RNA structure. Real-time quantitative PCR analysis of different hth splice isoforms and Northern blotting showed that the conserved element is associated with a high incidence of intron retention in hth pre-mRNA, suggesting that the conserved intronic element is critically important in the post-transcriptional regulation of hth expression in Diptera.

The role of insect cell lines in an artificial diet for the parasitold wasp, Trichogramma pretiosum

Trichogramma species are mass-produced for biological control using host eggs. Artificial diets have been developed to reduce production costs, however, most include insect haemolymph as a major component, which still results in a significant expense. Medium conditioned with insect cell lines has produced some success as a haemolymph replacement in artificial diets for several parasitoid wasp species. Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) was the first species to develop successfully to the adult stage on diets containing concentrated HeliothiS zea (Boddie) (Lepidoptera: Noctuidae) cells. Tricho-gramma pretiosum Riley (Hymenoptera: Trichogrammatidae) was subsequently grown to the adult stage on a similar cell line diet. This success encouraged a systematic investigation into the use of insect cell lines in Trichogramma artificial diets. We compared the effect of diets containing insect cells with diets containing conditioned cell line media. Diets containing insect cells produced significantly more pupae than diets containing conditioned medium and, although not significant, produced a higher number of adults. Second, we compared the effect of diets containing cell lines established from ovary-associated tissue of H. zea and embryo tissue of Aedes albopictus (Skuse) (Diptera: Culicidae) on T pretiosum development. Trichogramma pretiosum development was not significantly different on diets containing cells from the two origins and tissue types. Third, the effect of cell storage on T pretiosum development was observed. HeliothiS zea cells in medium were stored at 4 degrees C and room temperature (22 degrees C for one, two, four and seven days before addition to artificial diets. Cell viability was calculated for these storage treatments. HeliothiS zea cells could be stored at 4 degrees C for up to seven days with no detrimental effect on T pretiosum development. Tricho-gramma pretiosum development did not depend on cell viability. The use of insect cell lines as a haemolymph replacement has the potential to significantly reduce production costs and simplify Trichogramma artificial diets with the eventual aim of replacing host production in mass rearing facilities. (c) 2005 Elsevier Inc. All rights reserved.

A physiological product-release model for baculovirus infected insect cells

Existing models describe the product release from baculovirus infected insect cells as an unspecific protein leakage occurring in parallel with protein production. The model presented here shows that the observed product release of normally non-secreted proteins can be described through cell death alone. This model avoids the implicit non-physiological assumption of previous models that cells permeable to recombinant protein as well as trypan blue continue to produce protein. (c) 2005 Wiley Periodicals, Inc.