Year: 2014
Type: dissertation
Abstract: Epithelial sheets line the surfaces of the body and our organs, acting as semi-permeable barriers between the internal and external environment. Epithelial polarity is critical for epithelial function. In Drosophila, epithelial polarity is established at the onset of embryogenesis by a network of polarity, cytoskeletal, and junctional complexes. The scaffold protein Bazooka (Baz; mammalian partitioning-defective (PAR)-3), localizes to the site of adherens junction (AJ) assembly, where it acts as an early polarity landmark to position downstream AJ components. My work addressed how Baz positions AJ components, and how Baz is localized and positioned within the apicolateral region. The focus of my first study was to understand how Baz affects AJ assembly and what precursors were involved. The quantification of Baz and AJ components in combination with a photobleaching analysis suggested that early AJs are subdivided into Baz clusters and cadherin/catenin clusters with independent protein numbers and dynamics. Consistent with this idea, we identified cadherin/catenin clusters forming between apical microvilli. The Baz clusters appear to engage these cadherin-catenin clusters to assemble early AJs. For my second project, I investigated how Baz is recruited to the plasma membrane (PM) during late embryogenesis. I performed a structure-function analysis to determine the importance of each identified Baz interaction domain in regards to its localization and function in the Drosophila embryonic ectoderm. I found that a multifaceted membrane association mechanism localizes Baz to the apical circumference. Although none of the Baz protein domains are essential for cortical localization, I determined that each contributes to cortical anchorage in specific ways. I proposed that the redundancies involved may provide plasticity and robustness to Baz polarity landmarks. For my third project, I identified the coupling of two mechanisms that remove Baz from the basolateral region of the cell. As cells first form during cellularization, basally localized Baz puncta demonstrate basal-to-apical transport. The removal of all three Baz postsynaptic density/discs large/zonula occludens (PDZ) domains inhibits this transport mechanism. However, by the end of cellularization Baz without its PDZ domains becomes correctly localized, suggesting an additional mechanism removes basolateral Baz. Investigation of the basolateral kinase PAR-1 suggests it is responsible for this second mechanism.
Source: TSpace (University of Toronto)
Author: R. F. Andrew McKinley
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2473950142