Studies on mutagen-sensitive strains of Drosophila melanogaster III. A comparison of the mutagenic sensitivities of the ebony (UV and X-ray sensitive) and Canton-S (wild-type) strains to MMS, ENU, DEB, DEN and 2,4,6-Cl 3-PDMT

Abstract

The sensitivity of male germ cells of ebony (UV and X-ray sensitive) and Canton-S (wild-type) flies to the induction of sex-linked recessive lethals by 3 direct-acting mutagens (methyl methanesulphonate (MMS), N-ethyl- N-nitrosourea (ENU) and 1,2:3,4-diepoxybutane (DEB) and 2 chemicals that require metabolic activation ( N-nitrosodiethylamine (DEN) and 1-(2,4,6-trichlorophenyl)-3-3-dimethyltriazene (2,4,6-CI 3-PDMT) was investigated. In addition, experiments were carried out to examine whether mutational lesions induced by MMS, ENU and DEN in mature spermatozoa of males were processed differently by the oocytes of ebony and Canton-S flies (maternal effect studies). With all 3 direct-acting mutagens, the mutational responses of the post-meiotic male germ cells of the ebony and Canton-S flies were similar. After DEN treatment however, the ebony males responded with significantly lower frequencies of sex-linked recessive lethals in their pre- and post-meiotic germ cells. Measurements of microsomal P-450 enzymes revealed no detectable differences between the 2 strains with respect to either total cytochrome P-450 content or benzo[ a]pyrene hydroxylation activity; the p-nitroanisole demethylation activity however, was lower in the ebony than in Canton-S flies. With 2,4,6-C1 3-PDMT, the spermatids of ebony males responded with higher frequencies of recessive lethals than those of Canton-S males. The maternal effect studies provided no evidence for any differential processing of mutational lesions in the Canton-S and ebony females. The contrasting responses observed with DEN and 2,4,6-C1 3-PDMT have been explained on the basis of the assumption that in the ebony flies, there is an increased bioactivation of the triazene and a less efficient activation of DEN to their respective mutagenic metabolites, relative to the situation obtained in the Canton-S flies.