CUG and CAG Repeat RNA Pathogenesis in Drosophila Figure 2. Reducing Mbl levels does not enhance the tergite phenotype. A-D, Proportion of progeny within each phenotype category when repeat expression is driven by da-GAL4 alone (left column), or in the presence of the mblE27 mutant allele such that Mbl levels are reduced (right column). A, Wild-type control, B, 4xrCAA,100 [line 1], C, 4xrCUG,100 [line 1], D, 4xrCAG,100 [line 2]. E, F, Total proportion for each genotype that shows any phenotype (‘any phenotype’ - category 2, 3 and 4) and the proportion with a strong phenotype (‘strong phenotype’ – category 3 and 4). E, 4xrCUG,100 [line 1] shows a reduction in the proportion with any phenotype, but no change in the proportion with a strong phenotype with reduced Mbl levels. F, No significant effect was observed with 4xrCAG,100 [line 2]. Comparisons were made using Fisher’s exact test, with significant results indicated above the proportion, where *p,0.05. doi:10.1371/journal.pone.0038516.g002 the Dcr-2L811fsX mutant allele did not give a significantly different phenotype severity compared to repeat RNA expression in a wild-type Dcr-2 background (Figure 3E, F, S4 and Table S7). Thus, a reduction in Dcr-2 levels is not rate limiting for CAG or CUG repeat RNA-mediated tergite disruption. These results support tergite disruption being caused by a mechanism that is distinct to that responsible for Dcr-2 dependent double-stranded repeat RNA pathology. Reduced Dicer-1 Processing can have Opposing Effects on CUG or CAG RNA-mediated Tergite Phenotypes In Drosophila, Dcr-1 and Dcr-2 have distinct roles in small RNA biogenesis and therefore may have different preferences for hairpin-forming repeat RNA [60]. Thus, the ability of reduced Dcr-1 levels to modify tergite pathology was also examined. Repeat constructs were ubiquitously expressed using da-GAL4 in the presence of one copy of the Dcr-1Q1147X mutant allele and phenotype severity examined (Figure 4A-D, S5 and Table S6). In PLoS ONE | www.plosone.org 5 June 2012 | Volume 7 | Issue 6 | e38516