Genotoxicity of N-nitroso-N-methylurea and acetone oxime in the transgenic Drosophila carrying the human gene encoding a subunit of glutathione S-transferase.

The genotoxic effects of N-nitroso-N-methylurea (MNU) and acetone oxime (ACOX) were tested in the Somatic Mutation and Recombination Test (SMART) in Drosophila melanogaster. We have performed the same assay on transgenic flies expressing the human gene encoding a glutathione S-transferase alpha subunit (HGST). The SMART assay is used here to demonstrate genotoxicity and to determine the effect of human glutathione S-transferase on the genotoxic response. Three types of Drosophila strains were used: non-transgenic strains first described by Szabad (1986), transgenic strains derived from the Szabad strains but expressing the bacterial lacZ gene, and similarly derived transgenic strains expressing the HGST gene. MNU was highly genotoxic in both transgenic and non-transgenic flies. The non-transgenic lies were significantly more sensitive to the genotoxic effects of MNU compared to both types of transgenic flies. There were statistically significant differences between the transgenic HGST crosses and transgenic lacZ and non-transgenic control crosses but there was no significant difference between the genotoxic response to MNU in flies from the transgenic cross with lacZ and from the cross carrying three copies of HGST. ACOX also proved to be genotoxic to both non-transgenic and transgenic flies. However, flies carrying three copies of the gene were significantly more resistant to the genotoxic effect of ACOX than those transgenic flies with two or no copies of the human gene.