The relationship between lethal mutation yield and intake of ethylnitrosourea (ENU) in Drosophila melanogaster

Phenotyping of Drosophila melanogaster—A Nutritional Perspective

The model organism Drosophila melanogaster was increasingly applied in nutrition research in recent years. A range of methods are available for the phenotyping of D. melanogaster, which are outlined in the first part of this review. The methods include determinations of body weight, body composition, food intake, lifespan, locomotor activity, reproductive capacity and stress tolerance. In the second part, the practical application of the phenotyping of flies is demonstrated via a discussion of obese phenotypes in response to high-sugar diet (HSD) and high-fat diet (HFD) feeding. HSD feeding and HFD feeding are dietary interventions that lead to an increase in fat storage and affect carbohydrate-insulin homeostasis, lifespan, locomotor activity, reproductive capacity and stress tolerance. Furthermore, studies regarding the impacts of HSD and HFD on the transcriptome and metabolome of D. melanogaster are important for relating phenotypic changes to underlying molecular mechanisms. Overall, D. melanogaster was demonstrated to be a valuable model organism with which to examine the pathogeneses and underlying molecular mechanisms of common chronic metabolic diseases in a nutritional context.

EMS-induced polygenic mutation rates for nine quantitative characters in Drosophila melanogaster

Polygenic mutations were induced by treating Drosophila melanogaster adult males with 2.5 mM EMS. The treated second chromosomes, along with untreated controls, were then made homozygous, and five life history, two behavioral, and two morphological traits were measured. EMS mutagenesis led to reduced performance for life history traits. Changes in means and increments in genetic variance were relatively much higher for life history than for morphological traits, implying large differences in mutational target size. Maximum likelihood was used to estimate mutation rates and parameters of distributions of mutation effects, but parameters were strongly confounded with one another. Several traits showed evidence of leptokurtic distributions of effects and mean effects smaller than a few percent of trait means. Distributions of effects for all traits were strongly asymmetrical, and most mutations were deleterious. Correlations between life history mutation effects were positive. Mutation parameters for one generation of spontaneous mutation were predicted by scaling parameter estimates from the EMS experiment, extrapolated to the whole genome. Predicted mutational coefficients of variation were in good agreement with published estimates. Predicted changes in means were up to 0.14% or 0.6% for life history traits, depending on the model of scaling assumed.

The genotoxicity of nitrilotriacetic acid (NTA) in a somatic mutation and recombination test in Drosophila melanogaster

The genotoxicity of a chelating agent, the trisodium salt of nitrilotriacetic acid (NTA), was assessed in a somatic mutation and recombination test (SMART) in Drosophila melanogaster employing the wing hair markers mwh and flr3. The experiments were performed in parallel in two different laboratories (Padua, Italy and Schwerzenbach, Switzerland). The effectively absorbed doses of NTA, which was administered by feeding to larvae, were determined by a sensitive method employing [3H]leucine which allowed individual consumption levels to be measured. The particular pattern of clone induction produced by this compound suggests that NTA is active in inducing mitotic recombination and possibly aneuploidy in somatic cells of Drosophila. This is discussed in relation to the data present in the literature regarding the genotoxicity of NTA in a variety of experimental systems.

Current status of aneuploidy testing in Drosophila

Based on the literature on file at EMIC, 181 papers contained material on aneuploidy testing. Initial screening rejected papers providing no data, no negative control and/or poorly designed genetic schemes; 67 papers representing tests of 76 compounds were reported on. Statistical classifications were established as follows: (+)=a statistically significant difference at the 5% level between the treated and control frequencies; (-)=no significant difference at the 5% level when the number of offspring tested was sufficient to have identified an increase of 0.2% over the control with a power of 75%; I=inconclusive= (a) no significant difference at the 5% level but the number of offspring tested was below that necessary to detect an increase of 0.2% with a power of 75%; (b) the nature of apparent complete loss is undetermined; or (c) the nature of the germ cells sampled is not determined. Of the 76 compounds analyzed, calls were made on 34 compounds. 17/34 compounds were positive for chromosome gain (11/34 for chromosome gain and chromosome loss, 6/34 for chromosome gain only). 17/34 compounds were negative for chromosome gain (11/34 for chromosome gain and chromosome loss and 6 for chromosome gain only). Are any fo the compounds found to induce aneuploidy specific for aneuploid induction? 7 or the compounds positive for chromosome gain were positive in one or more tests assaying for other genetic endpoints, and no reliable data exists regarding results in other tests for the remaining 10 compounds; accordingly, the answer to the question awaits further work.

Linear relationship between lethal mutation yield and intake of ethyl methanesulfonate in Drosophila melanogaster

Males of Drosophila melanogaster were fed sucrose solutions containing various concentrations of EMS (from 0.25 to 10 mM) for 24 hr. To measure the intake of an EMS solution, 3H-labeled sucrose was added to the feeding solution, and the 3H activity inside the flies was used as a measure for the intake volume of EMS solution. Each absorbed dose of EMS was estimated from the intake volume of an EMS solution multiplied by its EMS concentration in the feeding solution in a way similar to that described in a previous report [Ayaki et al, 1984]. The relationship between the estimated absorbed dose and the exposure concentration was almost linear in a low concentration range but became concave with a downward curvature in a high concentration range. The dose-response relationship between the frequency of sex-linked recessive lethals and the estimated absorbed dose showed no deviation from linearity at all the five absorbed doses tested. It may be concluded that the absorbed doses thus estimated were very close to true absorbed doses, indicating the usefulness of the present method for dosimetry of chemicals to be given to flies.

Comparative studies of dose-response curves for recessive lethal mutations induced by ethylnitrosourea in spermatogonia and in spermatozoa of Drosophila melanogaster

Induction of recessive lethal mutations by N-ethyl-N-nitrosourea (ENU) was studied for the second chromosome of spermatogonia and spermatozoa in Drosophila melanogaster. ENU (0.03, 0.3, and 1.0 mM) was given to flies by dissolving it in feeding sucrose solution. Since flies are known to show increased avoidance of the feeding solution with increase in ENU concentration, the absorbed doses of ENU by flies were estimated from the previously determined empirical data for relation of ENU concentration in the feeding solution and the intake volumes of the solution by flies as measured indirectly via intake radioactivities of 3H-labeled sucrose added to the solution. When plotted against absorbed doses of ENU, the observed frequencies of recessive lethals showed a linear relationship for induction in spermatozoa but a sigmoidal relationship for induction in spermatogonia. These results suggest that in spermatogonia ENU-induced mutational damage is more repairable in a lower dose range of ENU. Mosaic lethal mutations were induced by ENU but not in spermatogonia.