PARENT SESSION
PT3 - Adaptation/Acquired Environmental Resistance
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P589) Characterization of ARNT and AHRR in Atlantic Tomcod.

Roy, Nirmal^*,1, Wirgin, Isaac¹, ¹ NYU School of Medicine, Tuxedo, NY, US

ABSTRACT- Atlantic tomcod Microgadus tomcodfrom the Hudson River exhibit an unusually high prevalence of heptocellular carcinomas, a truncated age structure, oncogene activation, high overall hepatic DNA damage, elevated hepatic burdens of PCBs/dioxins, and cytochrome P4501A1 (CYP1A1) mRNA expression compared to tomcod from cleaner estuaries. Yet, despite these manifestations of molecular/ organismic damage, CYP1A1 mRNA inducibility under controlled laboratory conditions with coplanar PCBs or TCDD is impaired in the Hudson River population. Additionally, tomcod from the Hudson River exhibit reduced sensitivity to B[a]P-induced early life-stage toxicity compared to tomcod from elsewhere. Because CYP1A1 transcription and most toxic responses from aromatic hydrocarbon exposure are mediated through the aryl hydrocarbon receptor (AHR) pathway, we hypothesize that down-regulation of AHR pathway function has contributed to resistance of the Hudson River population. In this study, we cloned and characterized the aryl receptor nuclear transporter (ARNT) and AHR repressor (AHRR) from tomcod cDNA and genomic DNA libraries. Sixteen exons were identified in the ARNT genomic DNA sequences and 1805 bp of ARNT cDNA was deduced from the genomic DNA. Sequence-specific primers were used to amplify ARNT mRNA and PCR products were sequenced to validate the deduced cDNA sequence. The deduced amino acid sequence of tomcod ARNT is 79.6% and 86.2% identical to that of mouse ARNT1 and rainbow trout ARNTa, respectively. Tomcod AHRR was also cloned and characterized and its cDNA is 73.4% and 66.4% identical to that of Fundulus heteroclitus and mouse, respectively. Also, 625 amino acid residues of the deduced tomcod AHRR peptide sequence is 74.3% and 72.1% identical to that of killifish and mouse, respectively. These results provide us with the molecular tools to compare the structure and expression of AHR, ARNT, and AHRR between resistant and sensitive populations of tomcod and to explore the molecular consequences of chronic exposure to aromatic hydrocarbons and other contaminants.

Key words: resistance, ARNT, aryl hydrocarbon receptor repressor, Atlantic tomcod