Journal Article

Identification of Methylmercury Tolerance Gene Candidates in Drosophila

Cecon T. Mahapatra, Jeffrey Bond, David M. Rand and Matthew D. Rand

in Toxicological Sciences

Volume 116, issue 1, pages 225-238
Published in print July 2010 | ISSN: 1096-6080
Published online April 2010 | e-ISSN: 1096-0929 | DOI: http://dx.doi.org/10.1093/toxsci/kfq097
Identification of Methylmercury Tolerance Gene Candidates in Drosophila

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Methylmercury (MeHg) is a ubiquitous environmental contaminant that preferentially targets the developing nervous system. Variable outcomes of prenatal MeHg exposure within a population point to a genetic component that regulates MeHg toxicity. We therefore sought to identify fundamental MeHg tolerance genes using the Drosophila model for genetic and molecular dissection of a MeHg tolerance trait. We observe autosomal dominance in a MeHg tolerance trait (development on MeHg food) in both wild-derived and laboratory-selected MeHg-tolerant strains of flies. We performed whole-genome transcript profiling of larval brains of tolerant (laboratory selected) and nontolerant (control) strains in the presence and absence of MeHg stress. Pairwise transcriptome comparisons of four conditions (+/−selection and +/−MeHg) identified a “down-down-up” expression signature, whereby MeHg alone and selection alone resulted in a greater number of downregulated transcripts, and the combination of selection + MeHg resulted in a greater number of upregulated transcripts. Functional annotation cluster analyses showed enrichment for monooxygenases/oxidoreductases, which include cytochrome P450 (CYP) family members. Among the 10 CYPs upregulated with selection + MeHg in tolerant strains, CYP6g1, previously identified as the dichlorodiphenyl trichloroethane resistance allele in flies, was the most highly expressed and responsive to MeHg. Among all the genes, Turandot A (TotA), an immune pathway–regulated humoral response gene, showed the greatest upregulation with selection + MeHg. Neural-specific transgenic overexpression of TotA enhanced MeHg tolerance during pupal development. Identification of TotA and CYP genes as MeHg tolerance genes is an inroad to investigating the conserved function of immune signaling and phase I metabolism pathways in MeHg toxicity and tolerance in higher organisms.

Keywords: methylmercury; MeHg; cytochrome P450; Turandot; immune pathways; stress response; alternative models

Journal Article.  9363 words.  Illustrated.

Subjects: Medical Toxicology ; Toxicology (Non-medical)

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