IFT20 is a member of the IFT B anterograde complex that is required for cilia formation and that, uniquely among IFT proteins, is found at the Golgi in addition to the centrosome and the cilium. Fluorescently-labelled IFT20 shuttles between the Golgi complex and the cilium and the ciliary microtubules (Follit et al, 2006; Follit et al, 2009). Golgi-association of IFT20 depends on interaction with the peripheral membrane protein TRIP11 and this interaction occurs independently of the IFT B complex (Follit et al, 2008). Golgi-localization of IFT20 is abolished in cells lacking TRIP11, and cilia in these cells are short and have a depleted complement of polycystin-2, a ciliary-localized membrane protein (Follit et al, 2008). RNAi-depletion of IFT20 in mammalian cells similarly compromises the traffic of polycystin-2 to the cilium (Follit et al, 2006). These data suggest that IFT20 may have a role at the Golgi complex in sorting and transporting membrane proteins that are destined for the cilium (Follit et al, 2006; Follit et al, 2008; Follit et al, 2009). IFT54, another IFT B component that is localized at the cilia, interacts with IFT20 but not with TRIP11, and overexpression of IFT54 displaces IFT20 from the Golgi. This supports a model where, after dissociation of the TRIP11:IFT20 complex, IFT54 docks IFT20 at the cilium, possibly on the surface of Golgi-derived vesicles, thus completing assembly of the IFT B complex and delivering ciliary membrane and membrane proteins to the site of cilium assembly (Follit et al, 2009; Omori et al, 2008; Li et al, 2008).
