IS THE WHITE-IVORY ASSAY OF DROSOPHILA-MELANOGASTER A USEFUL TOOL IN GENETIC TOXICOLOGY

The white-ivory assay of Drosophila is based on the detection of rever sions to wild-type phenotype of ommatidia with the white-ivory mutatio n. A tandem quadruplication of this gene is used in order to increase the reversion probability. Although the exact mechanism implicated in reversion is not known, revertant spots are believed to arise as a con sequence of intrachromosomal recombination or related phenomena. Since the white-ivory assay has not been broadly used, the number of chemic als tested until now is still limited. In this work, we have essayed 2 5 chemicals belonging to several chemical groups, i.e., crosslinking a gents, DNA-topoisomerase inhibitors, ant; metabolites/nucleotide pool inhibitors, cyclic-adduct inducers, halogenated hydrocarbons, bulky-ad duct inducers, intercalating agents, oxidative damage inducers, and a multiple damage inducer, to validate this test. Cross-linking agents, halogenated hydrocarbons, and the multiple damage inducer, daunomycin, were positive. On the contrary, the three antimetabolites/nucleotide pool inhibitors tested were negative. The other chemical groups showed disparate results, since some chemicals were positive, whereas others were negative in each group. A comparison with the results obtained i n the w/w(+) and mwh/flr(3) assays shows that the w(i) assay detects a more restricted spectrum of damages than those, although, with respec t to carcinogenicity, its sensitivity (0.76, with the 62 chemicals tes ted until now) is similar to that estimated for the mentioned somatic assays. The conclusion of this work, then, is that the w(i) assay is n ot recommended as a general screening test, because the background rev ersion frequencies show a high variability among solvents, the range o f lesion-recognition is lower than in the w/w(+) and mwh/flr(3) SMARTs , and the mechanism implicated in the white-ivory reversion is poorly understood. (C) 1997 Wiley-Liss, Inc.