Effect of tumor promoter TPA on spontaneous and mitomycin C induced mitotic recombination in Drosophila melanogaster

It has been proposed that mitotic recombination is involved in tumor promotion. To test this idea, we investigated the effect of a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), on spontaneous and mitomycin C (MMC)-induced mitotic recombination in Drosophila melanogaster. The test system used was the wing-spot assay. Third instar larvae (mwh+/+flr) were treated with MMC (0-0.3 mM) for 6 h and fed media containing TPA (0-10 micrograms/ml), and the wings of surviving adults were analyzed for the presence of mutant spots. The results are: (1) MMC induced twin spots as well as single spots dose dependently (0.03-0.3 mM). (2) TPA itself did not induce twin spots or single spots in the range of doses examined (0.1-10 micrograms/ml). (3) TPA did not enhance the frequencies of twin or single spots induced by MMC. These results indicate that TPA induced neither mitotic recombination nor mutations under these experimental conditions. Thus the results would not support the mitotic recombination theory in tumor promotion. Rather, in this study, TPA posttreatment resulted in reduced frequencies of mutant single spots induced by MMC.