Role of a Class Dhc1b Dynein in Retrograde Transport of Ift Motors and Ift Raft Particles along Cilia, but Not Dendrites, in Chemosensory Neurons of Living Caenorhabditis elegans

The heterotrimeric motor protein, kinesin-II, and its presumptive cargo, can be observed moving anterogradely at 0.7 μm/s by intraflagellar transport (IFT) within sensory cilia of chemosensory neurons of living Caenorhabditis elegans, using a fluorescence microscope–based transport assay (Orozco, J.T., K.P. Wedaman, D. Signor, H. Brown, L. Rose, and J.M. Scholey. 1999. Nature. 398:674). Here, we report that kinesin-II, and two of its presumptive cargo molecules, OSM-1 and OSM-6, all move at ∼1.1 μm/s in the retrograde direction along cilia and dendrites, which is consistent with the hypothesis that these proteins are retrieved from the distal endings of the cilia by a retrograde transport pathway that moves them along cilia and then dendrites, back to the neuronal cell body. To test the hypothesis that the minus end–directed microtubule motor protein, cytoplasmic dynein, drives this retrograde transport pathway, we visualized movement of kinesin-II and its cargo along dendrites and cilia in a che-3 cytoplasmic dynein mutant background, and observed an inhibition of retrograde transport in cilia but not in dendrites. In contrast, anterograde IFT proceeds normally in che-3 mutants. Thus, we propose that the class DHC1b cytoplasmic dynein, CHE-3, is specifically responsible for the retrograde transport of the anterograde motor, kinesin-II, and its cargo within sensory cilia, but not within dendrites.