Regulation of cytochrome P450 genes in drosophila melanogaster by the chemical environment
Cytochrome P450 monooxygenases (P450s) play an important role in the adaptive response of insects and other animals to chemicals in the environment. P450s are heme-dependent enzymes that catalyze the addition of oxygen to a substrate in the presence of an electron donor, such as NADPH. In insects, some P450s are phase I detoxificaiton enzymes, representing the first line of defense against lipophilic xenobiotics, while other P450s are involved in the biosynthesis of ecydsone, juvenile hormone and pheromones. P450s are tightly regulated throughout development, and P450s involved in detoxification have been shown to be substrate-inducible, instead of indiscriminately, constitutively expressed. Understanding constitutive and inducible expression requires knowledge about the regulatory pathways that control insect P450 expression, which is still lacking for most identified insect P450s. Drosophila melanogaster, because of its longstanding use as a genetic model organism, is a powerful tool for identifying possible regulatory mechanisms and for following expression through to function. The aim of this work is to examine the evolution of cytochrome P450 genes in D. melanogaster in response to xenobiotic compounds. First, I explore the role of constitutive and inducible expression of P450s in cross-tolerance of a methoprene-tolerant D. melanogaster strain to the fungal toxin, aflatoxin B1, a natural constituent in the diet. Next, I investigate the duplication of a xenobiotic-responsive P450 in D. melanogaster and across 11 Drosophila species and examine the changes incurred in a strain selected for DDT resistance. Finally, I address the function of a brain-specific P450 that is highly conserved across Drosophila species, by using a GAL4/UAS RNAi system to study the reproductive effects of knocking down the gene Cyp4g15. Using molecular modeling of the Cyp4g15 protein, I propose a potential substrate for this enzyme, the pheromone cis-vaccenyl acetate.
xenobiotics, gene expression, evolutionary toxicogenomics
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign