INDUCTION OF RAS ONCOGENE MUTATIONS AND HEPATOCARCINOGENESIS IN MEDAKA (ORYZIAS-LATIPES) EXPOSED TO DIETHYLNITROSAMINE

Medaka (Oryzias latipes), a fish model for assessing the carcinogenic impact of environmental exposure to genotoxic chemicals, were subjecte d to 390 ppm of diethylnitrosamine (DEN) in an aqueous bath for 48 h. Histological examinations, at 5 and 7 months post-exposure, revealed t hat 11 of 17 fish developed hepatic neoplasms (hepatocellular carcinom as, cholangiomas and mixed hepato-cholangiocellular carcinomas). Genom ic DNA extracted from the livers of normal medaka was used to obtain a nd sequence the structure of ras gene exon 1 and exon 2. Comparing PCR -amplified products from exon 1 and 2 by hybridization with specific m utation containing probes and/or by sequencing of liver DNA from contr ol and exposed fish revealed an association of ras oncogene mutations and DEN-induced tumor formation. While none of the control fish showed any mutations, three of 11 fish with tumors had ras gene mutations. A ll three fish had mutations at codon 12 replacing glycine with asparti c acid, While one fish had an additional mutation at codon 16 replacin g lysine with threonine. In addition to identifying DEN-induced mutati ons at codon 12 of the medaka ras oncogene, the present study represen ts a first report of an in vivo association of hepatocarcinogenesis, i n any species, with a mutation at codon 16. Mutation at codon 16 and t umorigenesis has been previously predicted and artificially produced. Our study also supports the relevance of the medaka fish model for in vivo detection of the carcinogenic potential of environmental pollutan ts in sediments and biota of ambient water systems. Copyright (C) 1996 Elsevier Science Ltd