Oxidative stress and neurogenetic networks in Drosophila

DESCRIPTION (provided by applicant): Oxidative stress resulting from chemical exposure has been implicated as a contributing risk factor for a range of neurodegenerative diseases. However, it has been challenging to dissect genetic and environmental contributions to phenotypes that are difficult to quantify in genetically heterogeneous human populations, where it is also virtually impossible to control environmental exposure. Drosophila melanogaster provides a genetically tractable model system, because the genetic background and environmental conditions can be precisely controlled, the response to oxidative stressors, such as paraquat, can be measured precisely, and a range of locomotor behaviors can be quantified accurately by simple assays as spontaneous activity patterns, startle-induced locomotor reactivity, and climbing behavior. The objective of this proposal is to delineate the impact of chemically induced oxidative stress on genetic networks that are associated with locomotion phenotypes. The specific aims of this application are: (1) To identify perturbations of genetic networks that are associated with locomotor behaviors by chemically induced oxidative stress;and, (2) To identify DNA sequence variants associated with the effects of oxidative stress on locomotor behaviors in 192 inbred wild-derived lines with fully sequenced genomes. We will capitalize on natural variation in inbred wild-derived lines of Drosophila to construct genome-wide networks of covariant transcripts that are associated with locomotion phenotypes under control conditions and after chronic exposure to paraquat at a concentration that is not acutely lethal, but shortens lifespan. In addition we propose to associate DNA sequence variants in 192 inbred wild-derived Drosophila lines with fully sequenced genomes with variation in these behavioral phenotypes under control conditions and after paraquat exposure. These experiments will generate directional networks for each behavioral phenotype that will enable us to determine to what extent these networks respond to paraquat-induced oxidative stress. We will obtain information about the cellular processes represented by transcripts in these networks and their connectivity, and we will be able to provide functional context for un-annotated transcripts. Comparisons among the control and treatment condition will enable us to evaluate genotype by environment effects at the level of genetic networks and identify critical genes that drive the connectivity of the network under conditions of chemically- induced oxidative stress. Both the mechanisms by which cells respond to oxidative stress and by which oxidative stress leads to cellular damage are likely to show extensive phylogenetic conservation. Thus, superposition of human orthologs on the genetic networks that are associated with behavioral sensitivity to oxidative stress in Drosophila may reveal new universal pathways by which cells adapt to chemical stress or by which chemical stressors affect cell structure, metabolism and function. Such insights will be invaluable for human epidemiological studies on genetic susceptibility to environmental risk factors both by providing a genome-wide perspective of potential adverse effects and by identifying critical genes as potential targets for disease prevention. Health Relevance Environmental toxins, such as the herbicide paraquat, cause neuronal cell death through oxidative stress. Locomotor impairments are sensitive indicators of neurodegeneration. A long- standing challenge in environmental health science is to assess the effects of environmental chemicals such as pesticides or herbicides on genetic risk for neurodegenerative diseases as manifest through locomotor dysfunction (e.g. Parkinson's disease). Studies on genotype by environment interactions require a model system in which both the genetic background and the rearing environment can be controlled precisely. The fruit fly, Drosophila melanogaster, provides such a model. In this application we propose to capitalize on natural variation in inbred wild- derived strains of Drosophila to construct genome-wide networks of covariant transcripts that are associated with a range of locomotor phenotypes, including spontaneous activity, startle- induced locomotion, and gravitaxis, under control conditions and after chronic exposure to paraquat at a concentration that is not acutely lethal, but shortens lifespan. In addition we propose to associate DNA sequence variants in 192 inbred wild-derived Drosophila lines with fully sequenced genomes with variation in these behavioral phenotypes under control conditions and after paraquat exposure. The combined information from these two approaches will result in networks for each behavioral phenotype, in which direct or indirect regulatory interactions between components can be established. The effect of paraquat on these networks can be analyzed in detail. We will be able to determine to what extent these networks, associated with locomotor behaviors respond to paraquat-induced oxidative stress. We will obtain information about the cellular processes represented by these modules, the connectivity of transcripts within these networks, and the functional context of unannotated transcripts. Comparisons among the control and treatment condition will enable us to evaluate genotype by environment effects at the level of genetic networks and identify critical genes that drive the connectivity of the network under conditions of chemical environmental stress. Both the mechanisms by which cells respond to oxidative stress and by which oxidative stress leads to cellular damage are likely to show extensive phylogenetic conservation. Thus, superposition of human orthologs on the genetic networks that are associated with behavioral sensitivity to oxidative stress in Drosophila may reveal new universal pathways by which cells adapt to chemical stress or by which chemical stressors affect cell structure, metabolism and function. Such insights will be invaluable for human epidemiological studies on genetic susceptibility to environmental risk factors both by providing a genome-wide perspective of potential adverse effects and by identifying critical genes as potential targets for disease prevention.