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Polyploid cells have been associated with malignant neoplasms in many animal species. Recent advances in the genetic engineering of aquatic vertebrates have made it possible to produce healthy rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) that are completely triploid (3n) or tetraploid (4n). The objectives of this study were to compare the effects of direct- and indirect-acting carcinogens on DNA repair and measure the relative binding of benzo[a]pyrene (B(a)P) to DNA in diploid and polyploid cells.
The level of DNA repair was measured in diploid and polyploid cells following an in vitro exposure to the direct-acting carcinogen N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) or the indirect-acting carcinogen B(a)P. A DNA repair assay was used to compare the effects of MNNG and B(a)P on nucleated erythrocytes and hepatocytes.
Diploid and polyploid hepatocytes responded more strongly to MNNG than to B(a)P. DNA repair activity per haploid genome in polyploid fish hepatocytes was found to be greater than in diploid hepatocytes. Tetraploid cells consistently exhibited slightly more than twice the unscheduled DNA synthesis of the diploid cells. Rainbow trout erythrocytes were completely refractory to MNNG and B(a)P in the DNA repair assay.
The 32P-postlabeling assay, which measures DNA-bound compounds, indicated that at least five distinct DNA adducts are formed in rainbow trout liver cells following exposure to B(a)P. Diploid and tetraploid cells were found to contain significant differences in the relative number of specific adducts. No adducts were detected in the DMSO solvent controls.
DNA repair, DNA adducts, polyploid, fish, hepatocytes, 32, P-postlabeling, MNNG, benzo[, a, ]pyrene
Rangen Aquaculture Research Center, Hagerman, ID
University of Washington WH-10, Seattle, WA