PARENT SESSION

PM10 Mechanisms of Toxic Action
Exhibit Hall
8:00 AM - Monday

(PM158) Molecular Characterization of the Aryl Hydrocarbon Receptors (AHR1 and AHR2) from Red Seabream (Pagrus major).

Yamauchi, M^{1, 2}, Kim, E-Y¹, Iwata, H², Tanabe, S², ¹ Ehime Prefectural Institute of Public Health and Environmental Science, Matsuyama, Ehime, Japan² Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime, Japan

ABSTRACT- Planar halogenated aromatic hydrocarbons (PHAHs) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds are ubiquitous environmental contaminants causing a wide range of toxic responses in a variety of vertebrate animals. Fishes are one of most sensitive groups to TCDD exposure. Red seabream (Pagrus major), belonging to Sparidae family, is an important fishery resource in Japan. Due to their higher trophic position in the food chain and long life, risk to PHAHs exposure may be more serious for this species than others. To investigate the potential sensitivity to toxic effects of PHAHs in red seabream, we initially cloned and sequenced cDNA of the aryl hydrocarbon receptor (AHR), an intracellular protein that mediates the PHAHs toxic effects. The present study identified two highly divergent AHR genes (rsAHR1 and rsAHR2), which share only 34% identity in full-length amino acid sequence. RsAHR1 encoded an 846-residue protein with a predicted molecular mass of 93.2kDa and is most closely related to medaka (Oryzias latipes) AHR1(69% overall amino acid identity). RsAHR2 encoded a 990-residue protein with a predicted molecular mass of 108.9kDa and is most closely related to killifish (Fundulus heteroclitus) AHR2 (53% overall amino acid identity). In the N-terminal, both rsAHR genes include bHLH and PAS domains, which participate in ligand binding, AHR/ARNT dimerization and DNA binding. The C-terminal half, which is responsible for transactivation, was poorly conserved between rsAHRs. Tissue expression patterns of rsAHR1 and rsAHR2 mRNAs were also examined in various tissues and organs using a quantitive real-time RT-PCR approach. Tissue expression patterns of rsAHRs were isoform- and species-specific, indicating distinct roles for each rsAHR in tissues and organs. Further study is needed on the functional characterization related to isoform- and species-specific expression of rsAHRs.

Key words: AHR2, AHR1, CYP1A, Red seabream