Cilia and flagella are important organelles involved in diverse functions such as fluid and cell movement, sensory perception, and embryonic patterning. They are devoid of protein synthesis, thus their formation and maintenance requires the movement of protein complexes from the cytoplasm into the cilium and flagellum axoneme by intraflagellar transport (IFT), a conserved process common to ciliated or flagellated eukaryotic cells. Mutations in murine Polaris ( Tg737 ) result in cystic kidney disease and left-right axis patterning defects associated with aberrant cilia formation or maintenance. Tg737 is expressed in ciliated epithelial cells, and the encoded protein, Polaris, localizes to the base of cilia and within the cilium axoneme. Here we characterize
osm-5, the C. elegans homologue of the murine cystic kidney disease gene Tg737.
osm-5 is expressed in ciliated sensory neurons and its expression is regulated by DAF-19, an RFX-type transcription factor, that governs the expression of several other genes involved in cilia formation in the worm. OSM-5 protein is predicted to contain ten tetratricopeptide repeats (TPRs), a motif involved in protein-protein interactions. Similar to murine Polaris, OSM-5 protein was found to concentrate at the cilium base and within the cilium axoneme by immunofluorescence and an OSM-5::GFP translational fusion. Furthermore, time-lapse imaging of OSM-5::GFP fusion protein shows fluorescent particle migration within the cilia. Analysis of three mutant
osm-5 alleles indicates that
osm-5 is required for cilia formation and that the TPRs are essential for proper function of the protein. Overall, our data support a conserved role for OSM-5 in ciliogenesis, most likely as a component of the IFT process.