Interplay between Ciliary Ultrastructure and IFT-Train Dynamics Revealed by Single-Molecule Super-resolution Imaging

Summary: Cilia are built and maintained by intraflagellar transport (IFT), driving IFT trains back and forth along the ciliary axoneme. How IFT brings about the intricate ciliary structure and how this structure affects IFT are not well understood. We identify, using single-molecule super-resolution imaging of IFT components in living C. elegans, ciliary subdomains, enabling correlation of IFT-train dynamics to ciliary ultra-structure. In the transition zone, IFT dynamics are impaired, resulting in frequent pauses. At the ciliary base and tip, IFT trains show intriguing turnaround dynamics. Surprisingly, deletion of IFT motor kinesin-II not only affects IFT-train dynamics but also alters ciliary structure. Super-resolution imaging in these mutant animals suggests that the arrangement of IFT trains with respect to the axonemal microtubules is different than in wild-type animals. Our results reveal a complex, mutual interplay between ciliary ultrastructure and IFT-train dynamics, highlighting the importance of physical cues in the control of IFT dynamics. : Oswald et al. use trajectories of single intraflagellar transport proteins in the chemosensory cilia of C. elegans to generate super-resolution fluorescence maps. Local motility properties can be correlated to ciliary ultrastructure. They find that in the absence of kinesin-II, the ciliary ultrastructure is substantially altered. Keywords: single-molecule fluorescence microscopy, super-resolution microscopy, intraflagellar transport, intracellular transport, cilia, motor cooperation, molecular motor proteins