CHARACTERIZATION AND PREVALENCE OF A POLYMORPHISM IN THE 3'-UNTRANSLATED REGION OF CYTOCHROME P4501A1 IN CANCER-PRONE ATLANTIC TOMCOD

Atlantic tomcod (Microgadus tomcod) from the cancer-prone Hudson River population exhibit a genetic polymorphism in the cytochrome P4501A (C YP1A) gene which is evidenced in Northern blot analyses by a truncated transcript and in Southern blot analyses by a deletion in the variant allele. To initially evaluate the functional significance of this pol ymorphism, we sought to characterize the molecular basis for this poly morphism and to determine its frequency in tomcod from other populatio ns in which the prevalence of neoplasia is low. The common CYP1A allel ic sequence was determined from beta-naphthoflavone-induced tomcod cDN A and from tomcod genomic DNA. A sequence of the variant CYP1A allele was obtained by direct sequence analysis of the amplicons of variant t omcod cDNA and genomic DNA. CYP1A exon and intron structure is highly conserved between tomcod and all other teleost and mammalian species c ompared. Similarity of the deduced tomcod, rainbow trout, and plaice a mino acid sequences was 72%, whereas similarity between tomcod and mam malian sequences was approximately 50%. The variant tomcod CYP1A allel e results from a 606-bp deletion in the 7th exon of the 3' untranslate d region (UTR) of the cDNA. Polymerase chain reaction and Northern blo t analyses revealed an absence of this CYP1A polymorphism in tomcod fr om other rivers. Studies in humans suggest that variation in CYP1A1 cD NA may impact on genetic susceptibility to environmentally induced neo plasia. Furthermore, studies in in vitro mammalian models indicate the importance of 3' UTRs on gene expression by impacting on the stabilit y of transcript. These results suggest that the 3' UTR CYP1A polymorph ism in tomcod may have consequences for the genetic susceptibility of Hudson River fish to hepatic neoplasia. (C) 1995 Academic Press, Inc.