Intraflagellar transport is required for the vectorial movement of TRPV channels in the ciliary membrane

The membranes of all eukaryotic motile (9 + 2) and immotile primary (9 + 0) cilia harbor channels and receptors involved in sensory transduction (reviewed by [1]). These membrane proteins are transported from the cytoplasm onto the ciliary membrane by vesicles targeted for exocytosis at a point adjacent to the ciliary basal body [2, 3]. Here, we use time-lapse fluorescence microscopy to demonstrate that select GFP-tagged sensory receptors undergo rapid vectorial transport along the entire length of the cilia of Caenorhabditis elegans sensory neurons. Transient receptor potential vanilloid (TRPV) channels OSM-9 and OCR-2 [4, 5] move in ciliary membranes at rates comparable to the intraflagellar transport (IFT) machinery located between the membrane and the underlying axonemal microtubules [6-8]. OSM-9 motility is disrupted in certain IFT mutant backgrounds. Surprisingly, motility of transient receptor potential polycystin (TRPP) channel PKD-2 (polycystic kidney disease-2) [9], a mechano-receptor [10], was not detected. Our study demonstrates that IFT, previously shown to be necessary for transport of axonemal components [11], is also involved in the motility of TRPV membrane protein movement along cilia of C. elegans sensory cells.