The use of the bipartite UAS/GAL4 expression system [24], and the remarkable number of promoters or enhancers available, of which TH-Gal4, elav-Gal4 and Ddc-Gal4 are utilized in modelling PD in flies [16–23], makes Drosophila a useful and albeit a powerful model organism. This evidence concerns the gene DDC and Parkinson disease.