Cilia are ubiquitous and important eukaryotic organelles that can be adapted for cell motility or sensory transduction. Microtubules (Mts) and MT-based motor proteins play critical roles in the formation of these structures. For example, recent work suggests that members of a subfamily of kinesins, the heteromeric kinesins, contain two distinct motor subunits, move to the plus ends of microtubules at approximately 0.4 mum.s-1, and play important roles in the assembly of cilia. The founding members of this subfamily, heterotrimeric kinesin-II from sea urchin, consists of distinct, heterodimerized motor subunits together with an accessory subunit, KAP115, and participates in the assembly of motile axonemes on blastula-stage embryos. In addition, two heteromeric kinesins, CeKinesin-II and CeOsm3-kinesin from Caenorhabditis elegans, are likely to participate in the assembly of sensory cilia on neurons. The research proposed here is aimed at understanding how the unique structural organization of the heteromeric kinesins is adapted to functioning in the assembly of these motile and sensory cilia. To this end, we will: 1) Use in vitro assays to probe the mechanisms of kinesin- II-driven motility and test the hypothesis that the heteromeric kinesins are adapted to moving along MT doublets in ciliary axonemes. 2) Test the hypothesis that kinesin-II drives the anterograde transport of essential ciliary components in sea urchin embryos. 3) Test the hypothesis that two heteromeric kinesins in C. elegans participate in sequential steps in the assembly of cilia, by mediating the anterograde transport of essential components from the neuronal cell bodies to the sensory cilia. By exploiting the complementary attributes of these two experimental systems, we should illuminate general principles concerning the role of microtubule based transport in the formation and function of cilia.
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