A local interplay between diffusion and intraflagellar transport distributes TRPV-channel OCR-2 along C. elegans chemosensory cilia

Single-molecule tracking of the sensory transmembrane protein OCR-2 in C. elegans reveals an interplay of transport modes during intraflagellar transport in the cilium. To survive, Caenorhabditis elegans depends on sensing soluble chemicals with transmembrane proteins (TPs) in the cilia of its chemosensory neurons. Cilia rely on intraflagellar transport (IFT) to facilitate the distribution of cargo, such as TPs, along the ciliary axoneme. Here, we use fluorescence imaging of living worms and perform single-molecule tracking experiments to elucidate the dynamics underlying the ciliary distribution of the sensory TP OCR-2. Quantitative analysis reveals that the ciliary distribution of OCR-2 depends on an intricate interplay between transport modes that depends on the specific location in the cilium: in dendrite and transition zone, directed transport is predominant. Along the cilium motion is mostly due to normal diffusion together with a small fraction of directed transport, while at the ciliary tip subdiffusion dominates. These insights in the role of IFT and diffusion in ciliary dynamics contribute to a deeper understanding of ciliary signal transduction and chemosensing.

Automated summary

In this study, single-molecule tracking experiments were used to investigate the interplay of transport modes during intraflagellar transport in the cilium. The distribution of the sensory transmembrane protein OCR-2 was found to depend on the specific location in the cilium, with directed transport predominant in the dendrite and transition zone, normal diffusion and a small fraction of directed transport along the cilium, and subdiffusion at the ciliary tip.