74 Oral - Cell Biology II
Friday April 08, 11:00 AM - 11:15 AM

Authors:
George Aranjuez; Travis Jewett

Affiliation: Immunity and Pathogenesis Division, College of Medicine, University of Central Florida, Orlando, FL

Keywords:
a. cytoskeleton; o. tissue growth and remodeling

Chlamydia trachomatis infection is the most frequently reported sexually transmitted infection in the United States. As an obligate intracellular bacterial pathogen, Chlamydia injects multiple protein effectors via the type III secretion system (T3SS) into the host cell to induce its entry. The early effector Tarp is required for efficient host cell entry by Chlamydia since a ΔTarp mutant has significantly reduced invasion frequency. Tarp is a ~150kDa protein with a tyrosine-rich N-terminal region and a C-terminal region that holds actin nucleating as well as F-actin bundling activities. Interestingly, removing Tarp’s F-actin bundling domain also impacts Chlamydia invasion. Studying the F-actin bundling activity of Tarp within the host cell has not been explored. Here, we use Drosophila as an in vivo cell biology platform to study Tarp’s F-actin bundling activity and how it impacts host cell biology. Ubiquitous expression of Tarp results in reduced adult viability and tissue-specific expression leads to various defects consistent with its ability to manipulate host actin. We used mechanosensory bristles as a model to study Tarp’s F-actin bundling activity since the establishment of bristle shape is dependent on proper F-actin bundling. Expressing Tarp in the thorax of wildtype flies leads to increased curvature of mechanosensory bristles. The growing pupal bristle is supported by parallel longitudinal F-actin bundles and the actin bundler Singed, required for normal bristle shape, localizes with the F-actin bundles. Surprisingly, Tarp expression in the bristles displaced Singed away from F-actin bundles. Tarp’s competitive behavior against Fascin during F-actin bundling was confirmed in vitro using co-sedimentation assay. Loss of either singed or forked in flies leads to highly deformed bristles. Strikingly, Tarp partially rescued the bristle morphology defect caused by singed knockdown. This work demonstrates the utility of Drosophila in studying bacterial effector function. Moreover, we provide in vivo confirmation of Tarp’s F-actin bundling activity and further uncovers a competitive behavior against Singed/Fascin during F-actin bundle assembly.