The analysis of parkin in Drosophila melanogaster

Haywood, Annika F. M. (2006) The analysis of parkin in Drosophila melanogaster. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Parkinson's disease (PD) is a highly prevalent neurodegenerative disease characterized by loss of motor control and resting tremor. Mutations in a number of genes, including α-synuclein and parkin, have been associated with inherited forms of PD and many of these genes are linked to the ubiquitin/proteasome degradation system (UPS). Studies of the effects of mutations in these genes suggest that impairment of the UPS is central to PD. Expression of wild-type or PD-associated forms of human α-synuclein in Drosophila melanogaster neurons recapitulates some of the symptoms of PD such as the loss of motor control, development of neuronal inclusions, and degeneration of dopaminergic neurons. Parkin, an E3 ubiquitin protein ligase, may be involved in targeting α-synuclein for degradation. To analyse this interaction I generated transgenic flies expressing parkin under the control of the yeast enhancer upstream activating sequence (UAS). The α-synuclein and parkin transgenes were expressed in combination to examine their interaction in vivo. I showed that expression of parkin prevents the toxic effects of both mutant and wild-type human α-synuclein. Although the yeast protein Gal4 is a key component of the UAS/Gal4 ectopic expression system in Drosophila melanogaster, I showed that this protein can be toxic. Transgenic flies that express high levels of Gal4 in the developing eye show elevated apoptosis in the eye imaginal disc, which leads to a disorganised ommatidial array in the adult. Suppression of apoptosis by expression of the caspase inhibitor p35 prevents this. High levels of Gal4 expression in dopaminergic neurons produce larvae that have excessive apoptosis in the brain and reduced longevity in adult flies. I showed that parkin can suppress apoptosis and development defects in the eye. The ability of parkin to counter the toxicity of exogenous and endogenous proteins may provide great insight into our understanding of toxic protein-induced diseases.

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