The mitotic kinesin Kif18A is essential for chromosome congression in mammalian cells. Based on the observation that its inactivation results in aberrantly long and hyperstable microtubules, Kif18A, together with its other orthologues of the kinesin-8 family, has been classified as a microtubule depolymerase. Recently, our in vitro studies identified Kif18A indeed as a unique kinesin that integrates both plus-end directed motility and microtubule depolymerizing activity. While it is clear that Kinesin-8 motors are critical for the dynamics of microtubules, only little is known about the regulation of their activity, the mechanism of their length-dependent microtubule depolymerization and potential post-metaphase functions in chromosome segregation. In this proposal, a combination of biochemical approaches and live-cell studies will be employed to gain insights into the spatial and temporal regulation of Kif18A in mammalian cells. In parallel, a small molecule screen will we performed to identify inhibitors of Kif18A that allow us to dissect potential functions of Kif18A in late mitosis and/or cytokinesis, without interfering with its reported function in prometaphase. Identification and characterization of Kif18A inhibitors and/or mutants will be used in single molecule imaging experiments to gain further insight in the mechanism of Kif18A-mediated microtubule depolymerization. Collectively, the proposed studies will contribute to a detailed understanding of the function and regulation of the Kinesin-8 motor Kif18A in mitosis, and, thus, will provide important insights into the mechanism of chromosome segregation and how errors in this process can lead to aneuploidy and tumor formation.