Model of ARL-13/Arl13b function. (A) Summary of arl-13(tm2322) ciliary phenotypes showing disrupted cilium ultrastructure/morphology and ciliary membrane protein localization and weakly destabilized anterograde IFT assemblies (e.g., reduced DS speeds). (B) Overexpression of IFT transgenes in tm2322 further destabilizes anterograde IFT assemblies, causing decoupling of OSM-3 and enhancement of cilium structure/morphology defects. OSM-3 retains the ability to dock with IFT/BBS assemblies in DSs. (C) Model of ARL-13/Arl13b function in WT cilia. Arl13b associates with ciliary membranes via palmitoyl anchors, where it regulates the function or functions of unknown effectors required to stabilize ciliary protein transport processes. Effectors may interact directly with transport machinery or, alternatively, regulate ciliary membrane or axonemal MT processes (e.g., membrane biogenesis/turnover or MT stabilization), which indirectly facilitate protein transport.