Control of intraflagellar transport : studies of the planar cell polarity effector Fuz, the small GTPase Rsg1, and the novel protein TTC29
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Cilia are small microtubule based protrusions found on most cells of the vertebrate body. In humans, defects in the structure or function of cilia results in a large class of developmental and homeostatic diseases known collectively as the ciliopathies. Ciliogenesis is accomplished by the concerted action of a number of molecular pathways including the intraflagellar transport (IFT) system. IFT is a group of ~20 highly conserved proteins that assemble into large macromolecular complexes known as trains. These trains act to carry cargo bi-directionally between the cell body and ciliary tip, via interaction with the microtubule motors kinesin and dynein. IFT train dynamics are required for both cilia structure and function, however the controls on these dynamics are still incompletely understood. Here, I present the first platform for study of IFT dynamics within vertebrate multiciliated cells, an understudied population with critical functions in development and homeostasis. Using this platform, I demonstrate that the planar cell polarity effector protein Fuz is required for IFT dynamics via its control of the cytoplasmic localization of a subset of IFT proteins. Subsequently, I find that a Fuz binding partner, the putative small GTPase Rsg1, is also required for IFT protein localization and dynamics. Additionally, I describe a role for Rsg1 in basal body docking, one of the earliest events of ciliogenesis. Finally, I show that the poorly studied protein TTC29 is required for a specific subset of IFT dynamic behaviors. These data reveal novel regulatory motifs for ciliogenesis and demonstrate, specifically, the complexities of IFT regulation in the cytoplasm and within the cilium itself. Finally, they suggest that multiciliated cells provide a tractable platform for generating robust datasets for the investigation ciliary dynamics. Such studies are critical for informing our understanding of the molecular etiology of human ciliopathic diseases.