The Intraflagellar Transport Protein IFT20 Is Associated with the Golgi Complex and Is Required for Cilia Assembly

TLDR

Eukaryotic cilia are assembled by intraflagellar transport, in which large protein particles composed of at least 17 polypeptides move along ciliary microtubules to deliver cargos from the cell body to the cilium. The IFT20 subunit localizes to the Golgi, basal body, and cilia, moves dynamically between these compartments, and its knockdown blocks ciliary assembly or reduces polycystin‑2 delivery, indicating that IFT20 mediates transport of ciliary membrane proteins from the Golgi to the cilium.

Abstract

Eukaryotic cilia are assembled via intraflagellar transport (IFT) in which large protein particles are motored along ciliary microtubules. The IFT particles are composed of at least 17 polypeptides that are thought to contain binding sites for various cargos that need to be transported from their site of synthesis in the cell body to the site of assembly in the cilium. We show here that the IFT20 subunit of the particle is localized to the Golgi complex in addition to the basal body and cilia where all previous IFT particle proteins had been found. In living cells, fluorescently tagged IFT20 is highly dynamic and moves between the Golgi complex and the cilium as well as along ciliary microtubules. Strong knock down of IFT20 in mammalian cells blocks ciliary assembly but does not affect Golgi structure. Moderate knockdown does not block cilia assembly but reduces the amount of polycystin-2 that is localized to the cilia. This work suggests that IFT20 functions in the delivery of ciliary membrane proteins from the Golgi complex to the cilium.