Detection of mutations in transgenic fish carrying a bacteriophage lambda cll transgene target

To address the dual needs for improved methods to assess potential health r isks associated with chemical exposure in aquatic environments and for new models for in vivo mutagenesis studies, we developed transgenic fish that c arry multiple copies of a bacteriophage lambda vector that harbors the cll gene as a mutational target. We adapted a forward mutation assay, originall y developed for lambda transgenic rodents, to recover cll mutants efficient ly from fish genomic DNA by lambda in vitro packaging. After infecting and plating phage on a hfl- bacterial host, cll mutants were detected under sel ective conditions. We demonstrated that many fundamental features of mutati on analyses based on lambda transgenic rodents are shared by transgenic fis h. Spontaneous mutant frequencies, ranging from 4.3 x 10(-5) in liver, 2.9 x 10(-5) in whole fish, to 1.8 x 10(-5) in testes, were comparable to range s in lambda transgenic rodents. Treatment with ethylnitrosourea resulted in concentration-dependent, tissue-specific. and time-dependent mutation indu ctions consistent with known mechanisms of action. Frequencies of mutants i n liver increased insignificantly 5 days after ethylnitrosourea exposure, b ut increased 3.5-, 5.7- and 6.7-fold above background at 15, 20, and 30 day s, respectively. Mutants were induced 5-fold in testes at 5 days, attaining a peak 10-fold induction 15 days after treatment. Spontaneous and induced mutational spectra in the fish were also consistent with those of lambda tr ansgenic rodent models. Our results demonstrate the feasibility of in vivo mutation analyses using transgenic fish and illustrate the potential value of fish as important comparative animal models.