Kif9 is an active kinesin motor required for ciliary beating and proximodistal patterning of motile axonemes

Abstract Most motile cilia have a stereotyped structure of nine microtubule outer doublets and a single central pair of microtubules. The central pair microtubules are surrounded by a set of proteins, termed the central pair apparatus. A specific kinesin, Klp1 projects from the central pair and contributes to ciliary motility in Chlamydomonas. The vertebrate orthologue, Kif9 is required for beating in mouse sperm flagella, but the mechanism of Kif9/Klp1 function remains poorly defined. Here, using Xenopus epidermal multiciliated cells, we show that Kif9 is necessary for ciliary motility as well as leads to defects in the distal localization of not only central pair proteins, but also radial spokes and dynein arms. In addition, single-molecule assays in vitro revealed that Xenopus Kif9 is a processive motor, though like axonemal dyneins it displays no processivity in ciliary axonemes in vivo. Thus, our data suggest that Kif9 plays both indirect and direct role in ciliary motility.