Characterizing the spargel, nutcracker, PI31 and FBXO9 homologues as models of Parkinson Disease in Drosophila melanogaster

Parkinson Disease is a progressive neurodegenerative disorder resulting from the premature destruction or improper function of dopamine producing neurons in the striatum of the brain. Symptoms include resting tremor, bradykinesia, rigidity, postural instability, gait abnormality and additional severe cognitive impairment. Although Parkinson Disease has historically been thought of as a disease with sporadic origin, there are a number of genetic links and specific gene mutations found conserved across patients. These mutations are typically found in genes responsible for the proper functioning of proteasome activity or intracellular organelle homeostasis. The upkeep and repair of mitochondria involves a number of components including Pink1, Parkin, and the Peroxisome-proliferator-activated receptor coactivator (PGC) family of genes. The PGC family of genes have a single homologue in Drosophila melanogaster known as spargel. In Chapter Two, I characterized this gene in neuronal tissues and found that altered gene activity in dopaminergic neurons leads to a decrease in longevity and locomotor ability over time, indicative of a Parkinson Disease like phenotype. In Homo sapiens the PGC family genes are regulated through the activity of an intermediate protein, PARIS. In Chapter Five I identified three potential homologues of the PARIS gene in D. melanogaster and compared altered expression of them in neuronal tissues resulting in the identification of a strong PARIS candidate and two novel genes involved in neuronal development. The proteasome complex acts upon and destroys proteins targeted for destruction by addition of a ubiquitin moiety. This process is undertaken by ubiquitin ligase complexes. The target specific component of many of these complexes are the F-box genes. Chapters Three and Four characterize two F-box genes implicated in H. sapiens PD and identifies putative D. melanogaster gene homologs. The results of this thesis provide expanded knowledge of both confirmed and putative D. melanogaster homologues of H. sapiens disease related genes and new model systems with which future study of disease mechanisms may be carried out

spargel, the PGC-1α homologue, in models of Parkinson disease in Drosophila melanogaster

Background Parkinson disease (PD) is a progressive neurodegenerative disorder presenting with symptoms of resting tremor, bradykinesia, rigidity, postural instability and additional severe cognitive impairment over time. These symptoms arise from a decrease of available dopamine in the striatum of the brain resulting from the breakdown and death of dopaminergic (DA) neurons. A process implicated in the destruction of these neurons is mitochondrial breakdown and impairment. Upkeep and repair of mitochondria involves a number of complex and key components including Pink1, Parkin, and the PGC family of genes. PGC-1α has been characterized as a regulator of mitochondria biogenesis, insulin receptor signalling and energy metabolism, mutation of this gene has been linked to early onset forms of PD. The mammalian PGC family consists of three partially redundant genes making the study of full or partial loss of function difficult. The sole Drosophila melanogaster homologue of this gene family, spargel (srl), has been shown to function in similar pathways of mitochondrial upkeep and biogenesis. Results Directed expression of srl-RNAi in the D. melanogaster eye causes abnormal ommatidia and bristle formation while eye specific expression of srl-EY does not produce the minor rough eye phenotype associated with high temperature GMR-Gal4 expression. Ddc-Gal4 mediated tissue specific expression of srl transgene constructs in D. melanogaster DA neurons causes altered lifespan and climbing ability. Expression of a srl-RNAi causes an increase in mean lifespan but a decrease in overall loco-motor ability while induced expression of srl-EY causes a severe decrease in mean lifespan and a decrease in loco-motor ability. Conclusions The reduced lifespan and climbing ability associated with a tissue specific expression of srl in DA neurons provides a new model of PD in D. melanogaster which may be used to identify novel therapeutic approaches to human disease treatment and prevention