Lufenuron is an insect growth regulator insecticide mainly used for the control of the cat flea. To understand mechanisms of resistance to lufenuron, we have characterized lufenuron resistance in a natural population of Drosophila melanogaster. In this study we have used precise genetic mapping to identify a mechanism of lufenuron resistance: the overexpression of the cytochrome P450 gene Cyp12a4. Cyp12a4 is predicted to encode a mitochondrial cytochrome P450 enzyme. Expression of Cyp12a4 in D. melanogaster third-instar larvae was detected in the midgut and Malpighian tubules of both lufenuron-resistant and wild-type strains. The level of Cyp12a4 expression in the midgut is higher in the lufenuron-resistant strain than in wild-type strains. Driving the expression of Cyp12a4 in the midgut and Malpighian tubules by using the GAL4͞UAS gene expression system results in lufenuron resistance, but it does not result in resistance to three other insecticide classes. Transgenic expression of Cyp12a4 in a ubiquitous expression pattern results in late embryonic lethality, suggesting that high-level ectopic expression of Cyp12a4 is detrimental to development. cytochrome P450 ͉ insecticide resistance ͉ insect growth regulator ͉ genetic mopping I nsecticide resistance is an important example of natural selection (1). Resistance is predominantly mediated either by changes in the metabolism of the insecticide or by changes in the sensitivity of insecticide targets (2). Insecticide resistance mediated by target site modification is well documented for most commonly used insecticides (3-7). Molecular mechanisms of resistance due to increased insecticide metabolism by cytochrome P450s, esterases, and glutathione S-transferases are less well understood. Resistance is commonly found to be the result of up-regulation of single or multiple members of these enzyme families (8-13); however, resistance due to structural changes in enzymes has also been documented (14-16).Lufenuron is an insect growth regulator insecticide, mainly used in the control of the cat flea, Ctenocephalides felis. It is active against larval developmental stages, causing cuticular lesions resulting from the disruption of chitin synthesis (17). Lufenuron is also active against Diptera, including Drosophila melanogaster (18). To understand possible resistance mechanisms to lufenuron, we have used D. melanogaster as a model. Lufenuron resistance in D. melanogaster was originally reported in populations from two widely separated locations in the United States (19). As it was not expected that D. melanogaster had been in contact with lufenuron, it was postulated that this resistance resulted from cross-resistance that had evolved to an earlier, widely used insecticide (19). Subsequently, it was found that resistance to lufenuron was caused by the up-regulation of the cytochrome P450 gene Cyp6g1, which confers resistance to numerous insecticide classes, and that Cyp6g1-mediated resistance is widespread (8,20).Here we describe the discovery of a mechanism of lufenuron r...

Summary Although infections with virulent pathogens often induce a strong inflammatory reaction, what drives the increased immune response to pathogens compared to non-pathogenic microbes is poorly understood. One possibility is that the immune system senses the level of threat from a microorganism and augments the response accordingly. Here, focussing on cytotoxic necrotizing factor 1 (CNF1), an Escherichia coli-derived effector molecule, we showed the host indirectly sensed the pathogen by monitoring for the effector that modified RhoGTPases. CNF1 modified Rac2, which then interacted with the innate immune adaptors IMD and Rip1-Rip2 in flies and mammalian cells, respectively to drive an immune response. This response was protective and increased the ability of the host to restrict pathogen growth, thus defining a mechanism of effector-triggered immunity that contributes to how metazoans defend against microbes with pathogenic potential.

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