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Aryl hydrocarbon receptor polymorphisms and dioxin resistance in Atlantic killifish (Fundulus heteroclitus)

Hahn, Mark E; Karchner, Sibel I; Franks, Diana G; Merson, Rebeka R


The aryl hydrocarbon receptor (AHR) gene encodes a ligand-activated transcription factor through which planar halogenated aromatic hydrocarbons (HAHs) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as well as polynuclear aromatic hydrocarbons (PAHs) cause altered gene expression and toxicity. To understand the role of AHR genetic variability in differential sensitivity to HAHs and PAHs, we are currently studying a population of the teleost Fundulus heteroclitus (Atlantic killifish) that has evolved genetic resistance to the toxic and biochemical effects of these compounds. Here, we report that the killifish AHR1 locus is highly polymorphic and that the frequencies of the major allele types differ between dioxin-sensitive and dioxin-resistant populations. Twenty-five single nucleotide polymorphisms (SNPs), nine of which are non-synonymous, were identified in the AHR1 coding sequence. Seven identified alleles were assigned to three groups, designated AHR1*1, AHR1*2 and AHR1*3. AHR1*1 alleles were under-represented in a population of dioxin- and polychlorinated biphenyl (PCB)-resistant fish from a PCB-contaminated Superfund site (New Bedford Harbor, Massachusetts, USA) compared to dioxin-sensitive fish from a less contaminated reference site (Scorton Creek, Massachusetts, USA). To determine the possible role of these AHR1 variants in differential HAH sensitivity, we expressed representative variant proteins from the two most divergent allelic groups (AHR1*1 and AHR1*3) by in-vitro transcription and translation and assessed their functional properties. AHR1*1A and AHR1*3A proteins displayed similar binding capacities and affinities for [3H]TCDD. In transient transfection assays using mammalian cells, AHR1*1A and AHR1*3A exhibited similar abilities to support TCDD-dependent transactivation of a luciferase reporter gene under control of AHR-responsive enhancer elements. We discuss the possibility of other functional differences in AHR1 variants or their interaction with other killifish loci (AHR2, AHRR) that may contribute to differences in dioxin sensitivity.

Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.

Sponsorship: This work was supported in part by the Superfund Basic Research Program at the Boston University (National Institutes of Health grant 5 P42 ES07381) and NIH grant F32 ES05935 (R.R.M.).

Correspondence and requests for reprints to Mark E. Hahn, Biology Department, MS#32, Woods Hole Oceanographic Institution Woods Hole, MA 02543-1049, USA. Tel: +1 508 289 3242; fax: +1 508 457 2134; e-mail:

Received 28 October 2003 Accepted 19 November 2003

© 2004 Lippincott Williams & Wilkins, Inc.