IP02 Wildlife Toxicology
Room 13A/B, Level 4
8:00 AM - 12:00 PM, Wednesday, 12 November 2003
Chair: Forsythe, Barry ,
(IP12) Identification and molecular characterization of a novel aryl hydrocarbon receptor isoform (AhR2) in aquatic birds.
Kim, E-Y1, Yasui, T2, Iwata, H2, Tanab, S2, 1 Ehime Prefectural Institute of Public Health and Environmental Science, Matsuyama, Ehime, Japan2 Center for Marine Environmental Studies, Ehime University, Matsuyama, Ehime, Japan
ABSTRACT- Dioxins and its related planar halogenated aromatic hydrocarbons produces a wide range of toxic and biological effects, including hepato- and immuno-toxicity. Most of these effects are mediated by the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor that acts as a potent modulator of cellular growth and differentiation through the alteration of target gene expression. In most vertebrate species, only a single AHR has been isolated, while fish possess at least two AHR isoforms (AHR1 and AHR2), and these isoforms exhibited distinct properties for dioxin binding affinity and tissue-specific expression. Despite the speculations on the existence of AHR isoforms in other vertebrate species, there has been no reports on AHR isoforms in mammals and birds. Investigation of AHR isoforms in a variety of animals will provide useful information on the evolutional history and physiological function. In this study, we attempted to identify the AHR isoforms in birds, and succeeded in cloning and sequencing two AHR isoforms from the livers of a black-footed albatross (Diomedea nigripes) and a common cormorant (Phalacrocorax carbo) using RT-PCR and RACE methods. The two full-length AHR cDNAs from albatross were highly divergent (34% amino acid identity). A phylogenetic analysis showed that one of them belongs to AHR1 clade and another one belongs to AHR2 clade, which has been identified so far only from fishes but not yet from mammals and birds. This result strongly suggests that birds would also possess two distinct AHR genes (AHR1 and AHR2). Albatross AHR1 encoded a 862-residue protein with a predicted molecular mass of 96.7kDa, and in the case of albatross AHR2, 930 amino acids and 100.7kDa. From the liver of a cormorant, the full-length AHR1 cDNA (861 amino acids and 96.6kDa) and the partial-length AHR2 cDNA have been cloned. The presence of two AHR isoforms in birds is of interest when considering the fact that the distinct functions of each isoform might be responsible for mediating the toxic effects of dioxins.
Key words: bird, AhR