Identification of genetic interactions in a S. pombe yeast model for juvenile CLN3 disease

Juvenile CLN3 disease is a rare lysosomal storage disease, and the most common cause of neurodegeneration in children. Since the identification of the disease gene (CLN3) in 1995, efforts in various cellular and animal models have led to CLN3 being associated with several cellular pathologies. However, its precise molecular function remains unknown. Furthermore, with only a limited knowledge of disease pathogenesis, there remains a considerable need to identify therapeutic targets in order to accelerate the development of therapies for this prematurely fatal disease. Schizosaccharomyces pombe has proved to be a powerful and accurate model to help elucidate the function of CLN3 by virtue of its evolutionary conserved orthologue, btn1+. To date it has revealed both a new cellular localisation and potential functions for btn1+. The primary aim of this project was therefore to further exploit this fission yeast (btn1∆) model, and use synthetic genetic array analysis (SGAs) to identify genome- wide, genetic interactions of btn1+. It was hypothesised that defining the genetic relationships of btn1+ would provide insight into its molecular role, which in turn could be used to infer CLN3 gene function. It was also hoped that such information could be used to identify therapeutic targets and help refine the focus of future work in higher eukaryotic models. Using such an approach, this thesis provides a considerable step in our understand- ing of the function of btn1+, and by extrapolation CLN3, by suggesting that their function likely converges with various stress response pathways. A comprehensive characterization of the btn1∆ strain revealed numerous phenotypes co-incident with known stress response mutants, suggesting that this strain indeed displays compromised stress signalling which may contribute to disease pathogenesis. This thesis also details a number of therapeutic targets as the genetic manipulation of two highly conserved mitogen activated protein kinase pathways (the cell wall integrity (CWI) pathway and stress associated protein kinase (SAPK) pathway) and the interconnected TOR kinase complexes, are shown to rescue aspects, if not all, of the btn1∆ phenotypes investigated. This is the most successful rescue of disease phenotypes in any model for juvenile CLN3 disease to date