Functional aspects of ciliary maintenance in Caenorhabditis elegans

Primary cilia are cellular antennae found on many cell types in metazoans. Their biogenesis and maintenance is critical throughout lifespan of an animal to support signal transduction pathways essential for development, and physiological processes such as vision and olfaction. Intraflagellar transport (IFT) is a process that is required to form and maintain cilia. Studies in Chlamydomonas reinhardtii and Caenorhabditis elegans have revealed several components required for ciliogenesis and IFT, but the function and mechanism of many of these proteins are poorly understood. In this dissertation, I identify and characterize two genes, che-10 and dyf-18, that maintain ciliary function at least in part by modulating IFT. I identified CHE-10 as the rootletin ortholog in C. elegans. Rootletin is an evolutionarily conserved protein that exists as polymerized striated rootlets, a cytoskeleton-like structure associated to the cilium-nucleating basal bodies, or as non-filamentous form associated to the ciliary base. Similar to its disruption in mouse model, che-10 mutants initiate ciliogenesis but the cilia degenerate over time. I showed that rootletin maintains cilia by modulating the assembly, motility and flux of IFT components. I also demonstrated that rootletin is essential for the stability of the axoneme, the transition zone, which forms a ciliary gate, and the basal bodies. Finally, I present evidence that the molecular basis of these defects may be due to inefficient delivery of ciliary components and organization at the periciliary membrane compartment, leading to cilium degeneration. DYF-18, a C. elegans CCRK-related Ser-Thr kinase, was uncovered in a screen for genes expressed during ciliogenesis. I show that DYF-18 is expressed in all ciliated sensory neurons. Similar to C. reinhardtii, disruption of DYF-18 leads to ciliary length defects. Finally, I demonstrated that dyf-18 mutants have abnormal accumulation of key IFT components. Specifically, OSM-5 is at the base of cilia and OSM-3 kinesin accumulates between and middle and distal segments of the axoneme. Intriguingly, in spite of the loss of OSM-3 kinesin in the distal segments, dyf-18 mutants can build a full-length cilium. Altogether, my studies offer insights into functional aspects of two novel proteins required for the maintenance of ciliary function in C. elegans.