Carroll E. Nix

Regulation of insecticide resistance-related cytochrome P-450 expression in Drosophila melanogaster

Abstract Two protein bands, resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, account for most of the cytochrome P -450 in Drosophila melanogaster . P -450-A is ubiquitous among strains tested; whereas P -450-B is unique to certain strains. Dimethylnitrosamine demethylase activity is associated with P -450-B. Biochemical and genetic analyses showed that genes located on chromosome II were required for P -450-B expression. These genes were mapped within an interval that includes a major insecticide-resistance locus. Regulatory loci on chromosome III were required for maximum expression of P -450-B. One of these regulatory loci was mapped at another major resistance locus on chromosome III. There was a good correlation between P -450-B expression and resistance to phenylurea among the different strains tested. These results indicate that Drosophila can be a useful model to study the molecular mechanisms of insecticide resistance.

Natural variation in the expression of cytochrome P-450 and dimethylnitrosamine demethylase in Drosophila

Electrophoresis of Drosophila microsomes resolves two major heme-containing protein bands with apparent molecular weights of 59,290 (band a) and 55,750 (band b). The hemoproteins in these two bands can account for most of the cytochrome P-450 in the organism. Band a is present in all strains examined: band b is not. Dimethylnitrosamine demethylase, a P-450 enzyme, is a component of band b.

Effects of N-nitrosopiperidine substitutions on mutagenicity in Dosophila melanogaster☆☆☆

N-Nitrosopiperidine (NP) and various derivatives were fed to Drosophila melanogaster males over a wide concentration range in order to assess their mutagenic potency in the induction of X-linked recessive lethals and chromosome loss. NP was effective in inducing lethals, as were its halogen and methyl-substituted derivatives, with the exception of 2,6-dimethyl NP. (Methyl substitutions at the alpha carbon atoms reduce or eliminate mutagenic activity.) Substitution of halogen groups on the piperidine ring enhanced the mutagenic activity, with the 3-chloro compound being the most mutagenic. In contrast, substitutions with a hydroxyl, carboxyl, or keto group resulted in a loss of mutagenicity. None of the compounds tested increased the frequency of chromosome loss or breakage in mature sperm.

Effects of methylation and ring size on mutagenicity of cyclic nitrosamines in Drosophila melanogaster.

The mutagenic activity of 7 nitrosopiperazines, 2 nitropyrrolidines, and 3 nitrosomorpholines was examined in the X-linked recessive-lethal assay of Drosophila melanogaster. Mutagenicity is also reported for a series of cyclic nitrosamines that differ in structure only in the number of carbon atoms in the ring. Of the 18 compounds tested, 6 (nitrosopiperazine; 2,3,5,6-tetramethyldinitrosopiperazine; nitrosoproline; 2,5-dimethylnitrosopyrrolidine; nitrosothiomorpholine; and nitrosooctamethyleneimine) were nonmutagenic. As we reported earlier in investigations with the nitrosopiperidines, substitutions with methyl groups at all of the alpha-carbon atoms reduce or eliminate the mutagenic activity of dinitrosopiperazine and nitrosopyrrolidine.

Effects of genotype and age on mixed-function oxidase activities in adult Drosophila melanogaster.

The mixed-function oxidases that metabolize dimethylnitrosamine, aminopyrine, benzphetamine, 7-ethoxycoumarin and benzo[alpha]pyrene were measured in adults of the Canton-S, Oregon-R and Hikone-R strains of Drosophila melanogaster. The expression of these activities is both genotype and age dependent.

THE ROLE OF DROSOPHILA IN CHEMICAL MUTAGENESIS TESTING

An important question facing our society is the impact of numerous chemical insults on the health of man and his environment. Faced with a staggering array of chemicals and enormous testing costs, we can test only a few chemicals for possible carcinogenic effects. Recent results with the Salmonella/mammalian microsome mutagenesis assay developed by Ames (2), demonstrating a striking correlation between carcinogenicity and mutagenicity of many chemical compounds, offer the possibility that mutagenesis assay systems can provide a quick identification of potential carcinogens. Results from microbial assays can serve as a guideline for further mutagenesis testing as well as identify those compounds requiring more extensive analysis in mammalian systems.

Dimethylnitrosamine demethylase activity in Drosophila,melanogaster

A dimethylnitrosamine (DMN) demethylase with levels of activity comparable to that in uninduced rat liver was demonstrated in both larval and adult forms of the Hikone-R strain of Drosophila. A microsomal enzyme, it has many properties of a cytochrome P-450-containing mixed-function oxidase. Kinetic analysis indicates only a single enzyme with an apparent K/sub m/ of 10.5 mM DMN.