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Precise spatial and temporal control of cellular adhesion and signal transduction events are necessary for accurate animal development. Given the necessity for cell communication in carrying out processes like cell fate specification, growth, cell migration and differentiation, it is not surprising that signaling transduction pathways, such as EGFR, BMP, Notch, Wingless and Hippo, are intimately involved. All these pathways encompass a cascade of molecular events over which there is exquisite spatial and temporal control. A wide array of mechanisms, involving a diverse set of molecules, acts to provide this regulatory control. One such molecule implicated in the BMP signaling pathway in Drosophila development is Kek5, a Leucine rich repeat and Immunoglobulin domain (LIG) family member. Here I show that Kek5 modulates both BMP signaling and adherens junctions. For these functions, I further demonstrate that structural elements in both extracellular and intracellular region of Kek5 are critical, providing new insight into the LIG family and their roles in signaling pathways.

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Bacterial infection of mucosal epithelial cells triggers cell exfoliation to limit the dissemination of infection within the tissue. Therefore, mucosal pathogens must possess strategies to counteract cell extrusion in response to infection. Chlamydia trachomatis L2 spends most of its intracellular development in the non-infectious form, and premature extrusion of the host cell is detrimental to the pathogen. Here I show that Chlamydia trachomatis L2-infected cells exhibited increase adhesion as demonstrated by increased resistance to detachment by mild trypsinization. In addition, I observed an increase in the number and size of the focal adhesions of the Chlamydia trachomatis L2-infected cells. I demonstrated that this phenotype was not exclusive of C. trachomatis serovar L2 and that it was not restricted to a single type of cell line. Quantitative confocal and live-cell TIRF microscopy revealed that this bacterium actively modulated host cell focal adhesions by enhancing their stability. Infection conferred resistance to disassembly upon inhibition of myosin II or ROCK1 activity. Furthermore, I was able to demonstrate that the Chlamydia trachomatis effector TarP is able to colocalize to the sites of focal adhesions when ectopically expressed in mammalian cells. This resulted in increased number of the host cell focal adhesions. TarP was also able to confer resistance to myosin II inhibition, in a VBD-dependent manner. Also, I have found that C. trachomatis transmembrane protein CT228 cooperates with TarP to confer resistance to ROCK1 inhibition. Super resolution microscopy revealed a reorganisation of focal adhesions in Chlamydia trachomatis L2-infected cells. In summary, this work shows for the first time that Chlamydia trachomatis L2 uses TarP and CT228 to modulate the host cell focal adhesions. Finally, I have also described that both Chlamydia trachomatis L2 and TarP are able to alter the nanoscale architecture, this has never been reported in any other system.