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Editor's Highlight: Genetic Targets of Acute Toluene Inhalation in Drosophila melanogaster
Citation:
Bushnell, P., W. Ward, T. Morozova, W. Oshiro, M. Lin, R. Judson, S. Hester, J. Mckee, AND M. Higuchi. Editor's Highlight: Genetic Targets of Acute Toluene Inhalation in Drosophila melanogaster. TOXICOLOGICAL SCIENCES. Society of Toxicology, RESTON, VA, 156(1):230-239, (2017).
Impact/Purpose:
Interpretation and use of data from high-throughput assays for chemical toxicity require links between effects at molecular targets and adverse outcomes in whole animals. The well-characterized genome of Drosophila melanogaster provides a potential model system by which phenotypic responses to chemicals can be mapped to genes associated with those responses, which may in turn suggest adverse outcome pathways (AOPs) associated with those genes. This study evaluated the utility of Drosophila Genetics Reference Panel (DGRP), a collection of ~200 homozygous lines of fruit flies whose genomes have been sequenced, as an approach to identifying AOPs. A genome-wide association analysis of the narcotic effect of toluene on fruit flies using the DGRP identified 66 candidate genes that were associated with phenotypic variation for sensitivity to toluene, and human orthologs for 52 of these candidate Drosophila genes. None of the identified orthologs are presently known to be involved in canonical pathways for mammalian mechanisms of narcosis. Thus this analysis did not reveal a genetic signature of toluene-induced narcosis in mammals. Nevertheless, the list of identified human orthologs may provide insight into potential new pathways that could mediate the narcotic effects of toluene. This research suggests that more information about the biological processes associated with mammalian genes will be required to support this approach to identifying AOPs.
Description:
Interpretation and use of data from high-throughput assays for chemical toxicity require links between effects at molecular targets and adverse outcomes in whole animals. The well-characterized genome of Drosophila melanogaster provides a potential model system by which phenotypic responses to chemicals can be mapped to genes associated with those responses, which may in turn suggest adverse outcome pathways associated with those genes. To determine the utility of this approach, we used the Drosophila Genetics Reference Panel (DGRP), a collection of ~200 homozygous lines of fruit flies whose genomes have been sequenced. We quantified toluene-induced suppression of motor activity in 123 lines of these flies during exposure to toluene, a volatile organic compound known to induce narcosis in mammals via its effects on neuronal ion channels. We then applied genome-wide association analyses on this effect of toluene using the DGRP web portal (http://dgrp2.gnets.ncsu.edu), which identified polymorphisms in candidate genes associated with the variation in response to toluene exposure. We tested ~2 million variants and found 82 polymorphisms located in or near 66 candidate genes that were associated with phenotypic variation for sensitivity to toluene at P < 5 x 10-5, and human orthologs for 52 of these candidate Drosophila genes. None of these orthologs are known to be involved in canonical pathways for mammalian neuronal ion channels, including GABA, glutamate, dopamine, glycine, serotonin, and voltage sensitive calcium channels. Thus this analysis did not reveal a genetic signature consistent with processes previously-shown to be involved in toluene-induced narcosis in mammals. The list of the human orthologs included Gene Ontology terms associated with signaling, nervous system development and embryonic morphogenesis; these orthologs may provide insight into potential new pathways that could mediate the narcotic effects of toluene.
