Cilia, motile or sensory devices protruding from most eukaryote cell surfaces, are microtubule-based hair like organelles that extend from the modified mother centriole (basal body). Cilia dysfunction has been linked to a wide spectrum of human disorders, now collectively termed ciliopathies. Intraflagellar transport (IFT), a bidirectional movement of protein particles along the cilia axonemal microtubule, is required for cilia assembly and maintenance. However, little is known about how IFT particles assemble at the ciliary base. Here, we isolated a new C.elegans ciliogenesis mutant
jhu455, which encodes an uncharacterized protein DYF-17. GFP-tagged DYF-17 only label cilia base. Double staining with other cilia base markers indicated DYF-17 locates between the dendritic tip and the proximal end of the transition zone. In
jhu455 animals, cilia are truncated. Interestingly, most IFT-B components could enter into the residual cilia, whereas IFT-A proteins only accumulate around the ciliary base and show no ciliary staining. IFT cargo proteins (ciliary membrane receptors) were also found to mislocalize in
jhu455 background. These observations indicate a role for DYF-17 in regulating proper assembly of IFT particles at the ciliary base. Remarkably, we found that, in all IFT components examined, only DYF-11 (an IFT-B polypeptide) exhibits a unique mutant phenotype with abnormal and strong accumulation below the transition zone, the exact site where DYF-17 locates. DYF-11 was reported to be essential for IFT assembly and bridge the association of IFT machinery and membrane cargos. Our data showed that
dyf-11 mutants completely photocopy the mutant phenotypes of
jhu455 animals. Furthermore, we found that the mammalian homolog of DYF-17 locates at the distal appendage of mother centriole in immuno-EM assay and co-immunoprecipitated with mammalian DYF-11 homolog MIP-T3. Knockdown of mammalian DYF-17 abolishes the ciliary localization of MIP-T3 and compromises the cilia formation. Taken together, our data support a highly conserved ciliogenesis pathway in which recruiting of DYF-11 by distal appendage protein DYF-17 is a prerequisite for the ciliary entry of DYF-11 and the downstream IFT assembly.