PRKN and Parkinson disease: For example, following the identification of mutations in PINK1, a PTEN-induced serine/threonine kinase 1, and in the E3 ubiquitin ligase Parkin, as causative genes in monogenic PD, flies were instrumental in identifying the role of these genes in mitochondrial biology (Clark et al., 2006; Park et al., 2006; Deng et al., 2008; Poole et al., 2008; Yang et al., 2008).