UBC Theses and Dissertations
A genetic analysis of mutagen-sensitive mutations on the second chromosome of Drosophila melanogaster Henderson, Daryl Stewart
Mutagen-sensitive (mus) mutations in Drosophila melanogaster render developing flies hypersensitive to the lethal effects of DNA-damaging agents. In general, mus mutations identify DNA repair-related genes. In this study, 5 new second chromosome mus mutations (mus205B¹, mus208B¹, mus209B¹, mus210B¹ and mus211B¹), selected on the basis of sensitivity to methyl methanesulfonate (MMS), were characterized using a variety of genetic tests. One test measured the MMS-sensitivity of double mutant mus strains compared to their component single mutants. Mutant interactions were examined in 8 double mus and in 2 triple mus strains containing combinations of mus201D¹, mus205B¹, mus208B¹, mus210B¹ and mus211B¹ (or mus211B²). These analyses have revealed predominantly synergistic and epistatic responses to MMS. Taken together with the findings of previous genetic and biochemical studies of Drosophila mus strains, these results suggest that 3 major repair pathways may operate in flies to correct damage caused by MMS. Mutagen cross-sensitivity data and the results of the interaction studies suggest that mus mutations might serve as rapid and sensitive bioassays of somatic genotoxicity caused by mutagens and carcinogens. To explore this possibility, a simple mutagen test system was devised employing triple mutant mus strains. One strain (mus208B¹ mus210B¹ mus211B²) was tested for sensitivity to 14 mutagens/carcinogens and 2 non-carcinogens. Eleven of the mutagens/carcinogens were readily detected as genotoxic. Both non-carcinogens were non-genotoxic. These preliminary results demonstrate the feasibility (and some limitations) of the proposed somatic genotoxicity assay and emphasize the need for further test validation using a larger chemical data base. The temperature-sensitive lethal mutation mus209B¹ was subjected to extensive genetic analyses and to temperature shift experiments during development. This locus was found to encode a product(s) that (1) is essential for viability at virtually all pre-imaginal developmental stages (the latter half of pupation appears to be an exception), (2) is necessary for wildtype levels of resistance to the genotoxic effects of MMS and ionizing radiation, and (3) is required for female fertility. Confirmation of the pleiotropic nature of this mutation was obtained by meiotic and cytogenetic mapping studies and by complementation tests with a series of allelic mutations. The mus209B¹ phenotypes are similar to ones conferred by mutations in Drosophila and yeast that disrupt various aspects of chromosome metabolism. In this context, some possible roles for mus209B¹ are discussed.
Item Citations and Data