Kif6 regulates cilia motility and polarity in brain ependymal cells.

Motile cilia on ependymal cells lining brain ventricular walls beat in concert to generate laminar cerebrospinal fluid (CSF) flow. Dyneins and kinesins are ATPase microtubule motor proteins that promote the rhythmic beating of cilia axonemes. Despite common consensus about the importance of axonemal dynein motor proteins, little is known about how kinesin motors contribute to cilia motility. Here, we show that Kif6 is a slow processive motor (12.2±2.0 nm/s) on microtubules in vitro and localizes to both the apical cytoplasm and the axoneme in ependymal cells, though dos not display processive movement in vivo. Using a mouse mutant that models a human Kif6 mutation in a proband displaying macrocephaly, hypotonia, and seizures, we find that loss of Kif6 function caused decreased ependymal cilia motility and subsequently decreased fluid flow on the surface of brain ventricular walls. Disruption of Kif6 also disrupts cilia orientation, the formation of robust apical actin networks, and stabilization of basal bodies at the apical surface. This suggests a novel role for the Kif6 motor in maintenance of ciliary homeostasis in ependymal cells.