Overexpression of DNA polymerase theta (Pol theta) in Drosophila melanogaster causes reduced hatch rate and sensitivity to nitrogen mustard. Anna Dukhovich, Kelly Beagan, Mitch McVey. Biology Department, Tufts University, Medford, Ma.

   DNA polymerase theta (Pol theta), encoded by the mus308 gene, participates in the repair of DNA double strand breaks in Drosophila melanogaster by a mechanism called alternative end joining. Previously, we reported that Drosophila with mutated versions of the Pol theta protein are more sensitive to interstrand crosslinking agents (Chan, 2008). The role of Pol theta mainly has been studied by mutating or knocking out mus308, but the effect of overexpression has not been considered. Recently, the proteins overexpression was noted to be significant in DNA stability: in a clinical study of untreated breast cancer patients, Pol theta expression was 3- to 26-fold higher in tumor than in normal tissues (Lemée et al., 2010). The purpose of this project was to investigate the effects of Pol theta upregulation in Drosophila. Pol theta was overexpressed by utilizing the UAS-Gal4 system, using either ubiquitin-Gal4 or nanos-Gal4 drivers. The overexpressors were analyzed for phenotypic defects and, in the case of ubiquitous overexpression, tested for sensitivity to interstrand crosslinking agent nitrogen mustard. We found that both types of Pol theta overexpressors have a lower hatch rate, and that Pol theta ubiquitous overexpressors are slightly more resistant to nitrogen mustard. From these results, the effect of Pol theta upregulation in Drosophila is presently unclear, but it appears that appropriate Pol theta levels are important for genomic stability. Further investigation of this protein in fruit flies can then be related to the role of Pol theta and its overexpression in human cancer.