Isolation and characterization of the Xanthine dehydrogenase gene of the Mediterranean fruit fly, Ceratitis capitata

Role of xanthine dehydrogenase and aging on the innate immune response of Drosophila

It has been proposed that uric acid is an important scavenger of deleterious oxygen species and peroxynitrite in biological systems. The cellular sources responsible for the generation of damage-causing reactive oxygen species (ROS) are widespread. Xanthine dehydrogenase (XDH) / oxidase (XOD) catalyzes the oxidation of xanthine to uric acid. The rosy (ry) gene encodes XDH/XOD in Drosophila melanogaster. XDH codes for uric acid which is a ROS scavenger. XOD however is an enzyme system implicated in ROS production. In this study, we investigated the roles of XDH in the fly's immune defense response to infection and in the aging process. We first compared ROS generation and nitric oxide (NO) level in the whole body and the gut of XDH mutant with those of wild type. Our results suggested that XDH has a protective effect with respect to both ROS and NO generations, particularly in the gut. We also examined the effect of a XDH deletion mutant on the relative sensitivity of the organism against bacterial infection, on the immune inducibility of antimicrobial peptides and on the effect of aging in the defensive response to infection. Our results strongly suggest that XDH plays an important role in the innate immune response and that the age-associated deterioration of the innate immune response might be, at least in part, associated with the loss of XDH activity in the aging process.

Gene silencing in phlebotomine sand flies: Xanthine dehydrogenase knock down by dsRNA microinjections

Lutzomyia longipalpis are vectors of medically important visceral leishmaniasis in South America. Blood-fed adult females digest large amounts of protein, and xanthine dehydrogenase is thought to be a key enzyme involved in protein catabolism through the production of urate. Large amounts of heme are also released during digestion with potentially damaging consequences, as heme can generate oxygen radicals that damage lipids, proteins and nucleic acids. However, urate is an antioxidant that may prevent such oxidative damage produced by heme. We investigated xanthine dehydrogenase by developing the RNAi technique for sand flies and used this technique to knock down the Lu. longipalpis xanthine dehydrogenase gene to evaluate its role in survival of adult females after blood feeding. The gene sequence of Lu. longipalpis xanthine dehydrogenase is described together with expression in different life cycle stages and RNAi knock down. Semi-quantitative RT-PCR of xanthine dehydrogenase expression showed a significant increase in expression after bloodmeal ingestion. Microinjection of dsRNA via the thorax of 1-day-old adult female sand flies resulted in approximately 40% reduction of xanthine dehydrogenase gene expression in comparison to flies injected with a control dsRNA. A significant reduction of urate in the whole body and excretions of Lu. longipalpis was observed after dsRNA xanthine dehydrogenase microinjection and feeding 96h later on rabbit blood. Sand flies injected with XDH dsRNA also exhibit significantly reduced life span in comparison with the mock-injected group when fed on sucrose or when rabbit blood fed, showing that urate could be indeed an important free radical scavenger in Lu. longipalpis. The demonstration of xanthine dehydrogenase knock down by dsRNA microinjection, low mortality of microinjected insects and the successful bloodfeeding of injected insects demonstrated the utility of RNAi as a tool for functional analysis of genes in phlebotomine sand flies.

Identification of candidate aldehyde oxidases from the silkworm Bombyx mori potentially involved in antennal pheromone degradation

Signal inactivation is a crucial step in the dynamic of olfactory process and involves various Odorant-Degrading Enzymes. In the silkworm Bombyx mori, one of the best models for studying olfaction in insects, the involvement of an antennal-specific aldehyde oxidase in the degradation of the sex pheromone component bombykal has been demonstrated over the three past decades by biochemical studies. However, the corresponding enzyme has never been characterized at the molecular level. Bioinformatic screening of B. mori genome and molecular approaches have been used to isolate several candidate sequences of aldehyde oxidases. Two interesting antennal-expressed genes have been further characterized and their putative functions are discussed in regard to their respective expression pattern and to our knowledge on aldehyde oxidase properties. Interestingly, one gene appeared as specifically expressed in the antennae of B. mori and associated in males with the bombykal-sensitive sensilla, strongly suggesting that it could encode for the previously biochemically characterized enzyme.