Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2008
Publication Date: 6/1/2008
Citation: Aikins, M.J., Schooley, D.A., Begum, K., Detheux, M., Beeman, R.W., Park, Y. 2008. Vasopressin-like peptide and its receptor function in an indirect diuretic signaling pathway in the red flour beetle. Insect Biochemistry and Molecular Biology 38: 740-748. Interpretive Summary: Maintenance of proper hydration and prevention of desiccation is an important function of the insect kidney, especially for insects in dry environments such as stored grain and cereal products. Until recently, very little has been known about the genes and proteins that are needed for the proper functioning of this vital organ in pest insects. We identified two important osmoregulatory proteins in the red flour beetle and showed that they have very potent, indirect effects on production of insect urine. There must be a still-undiscovered component of this system, which acts directly on the osmoregulatory organ. Each of these newly-discovered genes can become a target in screening assays for new biopesticides that disrupt maintenance of hydration and related physiological processes.
Technical Abstract: The insect vasopressin-like peptide (AVPL) is of special interest because of its potential function in the regulation of diuresis. Genome sequences of the red flour beetle Tribolium castaneum yielded the genes encoding AVPL and AVPL receptor, whereas the homologous sequences are absent in the genomes of the fruitfly, malaria mosquito, silkworm and honeybee, although a recent genome sequence of the jewel wasp revealed an AVPL sequence. The Tribolium receptor for the AVPL, the first such receptor identified in any insect, was expressed in a reporter system, and showed a strong response (EC50 =1.5 nM) to AVPL F1, the monomeric form having an intramolecular disulfide bond. In addition to identifying the AVPL receptor, we have demonstrated that it has in vivo diuretic activity, but that it has no direct effect on Malpighian tubules. However, when the central nervous system plus corpora cardiaca and corpora allata are incubated along with the peptide and Malpighian tubules, the latter are stimulated by the AVPL peptide, suggesting it acts indirectly. Summing up all the results from this study, we conclude that AVPL functions as a monomer in Tribolium, indirectly stimulating the Malpighian tubules through the central nervous system including the endocrine organs corpora cardiaca and corpora allata. RNA interference in the late larval stages successfully suppressed mRNA levels of avpl and avpl-receptor, but with no mortality or abnormal phenotype, implying that the AVPL signaling pathway may have been near-dispensable in the early lineage of holometabolous insects.