arl-13 mutants have deformed cilia and disrupted IFT. (A) Dye-filling assay was used to examine ciliogenesis. Phasmid cilia of arl-13 mutants showed a clear Dyf phenotype. Introduction of a copy of wild-type (WT) ARL-13::GFP but not ARL-13^R83Q::GFP, which carries a human pathogenic mutation, fully rescued the Dyf phenotype in arl-13 mutants. Overexpression of ARL-13 NT, ARL-13 PRQ, or ARL-13^R83Q::GFP had mild dominant-negative effects on ciliogenesis. At least 100 animals were scored per genotype (∼400 individual phasmid cilia were observed). (B) The ciliary localization of ARL-13^R83Q::GFP was normal. (C) Phasmid cilia expressing OSM-6::GFP. Note the bulblike accumulations in arl-13 mutants. (D) Phasmid cilia expressing various ciliary markers. In arl-13 mutants, the IFT-A component CHE-11::GFP and the kinesin-II motor KAP-1::GFP showed no accumulation along cilia, whereas IFT-B components (CHE-13::GFP and OSM-5::GFP), the IFT-B–associated motor OSM-3, and BBS proteins (BBS-7::GFP and BBS-8::GFP) aggregated in similar bulblike structures. (E) GFP-tagged CHE-11, KAP-1, OSM-6, and OSM-3 were expressed in wild-type and arl-13 worms, and IFT transport event ratios within middle segments of phasmid cilia were quantified. Note that the curves of the IFT-A component CHE-11 and kinesin-II subunit KAP-1 significantly shifted to the left for arl-13 mutants compared with wild-type worms, suggesting that significant amounts of IFT-A and the associated kinesin-II move at a slower rate in the mutants. In contrast, a right shift of the curves for the IFT-B component OSM-6 and the OSM-3 motor was observed, indicating that IFT-B and the associated OSM-3 motor tend to move at a faster rate in ARL-13–deficient cilia. In all figures, solid arrows indicate the TZs, dashed arrows point to the approximate middle to distal segment transition points, and arrowheads mark the distal ends. Statistical analysis was performed using a two-tailed paired Student’s t test. *, P < 0.01. Error bars indicate SEM. Bars, 5 µm.