German cockroach midgut ESTs: a tool for identifying genes involved in insecticide biotransformation

Gel bait insecticides currently used for the German cockroach control act via ingestion. Thus the gut region, especially the midgut region, is thought to be the main site for biotransformation of these insecticides. In spite of this, very little is known about insecticide biotransformation genes expressed in the midgut of the German cockroach. One efficient way of identifying such genes is through sequencing of midgut expressed sequence tags (ESTs). ESTs are short sequences of DNA obtained from cDNA library clones. ESTs can provide information about gene expression patterns, for example, in different tissues, organs, or developmental stages of an organism. In the present study, a German cockroach midgut EST library was constructed using mixed life-stages of an insecticide-resistant strain. Initially 384 clones were sequenced from the cDNA library and the resulting sequences were examined for genes encoding insecticide biotransformation enzymes. Through this screening we identified a number of genes belonging to cytochrome P450 monooxygenase, carboxylesterase, epoxide hydrolase, and conjugative enzyme families that are apparently expressed in the midgut. Quantitative real time PCR was also performed to determine the expression patterns of these genes in various developmental stages of resistant and susceptible strains. The gene expression patterns and utility of this data in understanding the detoxification and/or biotransformation of newer gel bait insecticides is discussed.