Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Biology

Supervisor

Dr. Jim Karagiannis

Abstract

This study investigates the role of Apl5p in the complex regulatory network of Schizosaccharomyces pombe, which ensures the faithful and reliable completion of cytokinesis. This network, referred to as the cytokinesis checkpoint, ensures successful cell division upon perturbances to the cytokinetic machinery (e.g. disruption of the actin cytoskeleton). Apl5p has been identified as a putative regulator of the cytokinesis checkpoint based on the hyper-sensitivity of apl5D mutants to the actin depolymerizing drug, Latrunculin A. Apl5p is an essential subunit of the conserved AP3 adaptor complex, which is suspected to be involved in vesicular trafficking. Thus, I hypothesized that Apl5p mediates the transport of materials which are necessary for cytokinetic regulation during stress. In this report, I show that apl5D mutants are inviable in the presence of LatA due to their inability to complete cytokinesis. Using live-cell imaging, I show that the mutant’s failure to complete cytokinesis results from an underlying inability to maintain the physical integrity of the actomyosin ring upon the initiation of constriction. Over-expression of Apl5p resulted in a dominant negative effect and impeded cell viability upon treatment of LatA (rather than conferring LatA resistance). Lastly, I determined the intracellular localization of Apl5p by monitoring Apl5-YFP fusion proteins. Given its role in vesicular trafficking, Apl5p was expected to localize to cytoplasmic vesicles at, or near, the site of cell division. Surprisingly, Apl5p-YFP fusion proteins were instead found to localize to small punctate structures within, or on, the cell nucleus. This contradicts both my hypothesis and our current understanding of the functions of the AP3 complex. Therefore, further research is necessary to determine the role of Apl5p in cytokinetic regulation, especially concerning its localization.


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