IFT–Cargo Interactions and Protein Transport in Cilia

The motile and sensory functions of cilia and flagella are indispensable for human health. Cilia assembly requires a dedicated protein shuttle, intraflagellar transport (IFT), a bidirectional motility of multi-megadalton protein arrays along ciliary microtubules. IFT functions as a protein carrier delivering hundreds of distinct proteins into growing cilia. IFT-based protein import and export continue in fully grown cilia and are required for ciliary maintenance and sensing. Large ciliary building blocks might depend on IFT to move through the transition zone, which functions as a ciliary gate. Smaller, freely diffusing proteins, such as tubulin, depend on IFT to be concentrated or removed from cilia. As I discuss here, recent work provides insights into how IFT interacts with its cargoes and how the transport is regulated.

TrendsDefects in intraflagellar transport (IFT), a process that moves proteins into cilia, cause disease in humans.IFT functions in ciliary assembly, maintenance, protein export, and probably ciliary signaling.Direct imaging of protein transport on IFT trains revealed that the amount of cargo attached to each train is regulated in a ciliary length-dependent manner.Structural analysis of IFT proteins and complexes revealed how tubulin, the major protein of cilia and flagella, binds to IFT.