How microtubule motors coordinate mitosis
To maintain their genomic integrity, eukaryotic cells must replicate their DNA faithfully and distribute it equally to the daughter cells. Mitotic defects lead to aneuploidy and cancer. This indicates that the mitotic mechanisms that are in place to allow faithful division have been compromised. The segregation of chromosomes is mediated by polarized and highly dynamic filaments, termed microtubules. Microtubules depend on motor proteins to assemble into a spindle and segregate chromosomes. These motors play key roles in cytoskeletal organization during cell division but also in cell migration, polarity, and axonal and cytoplasmic transport. However, the reductionist approach to studying these motors in isolation is not sufficient to understand their function in the cellular context. It remains unclear how the activities of individual motors and their interacting regulatory networks cooperate to generate physiological cellular function such as chromosome segregation. We aim to define how kinesin motors are modulated by their cargos to provide a specific output, and how the coordinated activities of kinesin motors are greater than the sum of their individual activities in vitro and in human cells.
Kinetochores and motors. CENP-E is a huge motor (312 kD), recruited to unattached kinetochores. CENP-E moves kinetochores along microtubules to facilitate chromosome alignment. How CENP-E associates with the kinetochore, how human CENP-E is activated to walk on microtubules and how CENP-E motor ensembles are coordinated to move chromosomes is currently not known. We are addressing these questions.
Mitotic motors and microtubule dynamics. Our lab has made new discoveries on the mechanism of mitotic microtubule depolymerases. While Kinesin-13 motors are major microtubule depolymerases, the role of Kinesin-8 motors in microtubule depolymerization remains controversial. We have shown using gene knockout that the Kinesin-8 Kif18b controls microtubule length to center the mitotic spindle at metaphase (Fig 1A, B). Using in vitro reconstitution, we reveal that Kif18b is a highly processive plus end-directed motor that uses a C-terminal non-motor microtubule-binding region to accumulate at growing microtubule plus ends (Fig 1C). This region is regulated by phosphorylation to spatially control Kif18b accumulation at plus ends and is essential for Kif18b-dependent spindle positioning and regulation of microtubule length (Fig 1D). Finally we demonstrate that Kif18b shortens microtubules by increasing the catastrophe rate of dynamic microtubules. Overall, our work reveals that Kif18b utilizes its motile properties to reach microtubule ends where it regulates astral microtubule length to ensure spindle centering.
Gigant, E., Stefanutti, M., Laband, K., Gluszek-Kustusz, A., Edwards, F., Maton, G., Lacroix, B., Canman, J.C., Welburn, J.P.I. , Dumont, J. (2017). Inhibition of ectopic microtubule assembly by the kinesin-13 KLP-7MCAK prevents oocyte aneuploidy. Development. 144:1674-1686.
Legal T., Zou J., Sochaj, A., Rappsilber, J., Welburn, J.P.I. (2016). Molecular architecture of the Dam1 complex-microtubule interaction. Open Biology. DOI: 10.1098. PMID: 26962051.
Talapatra, S., Harker, B., Welburn, J.P.I. (2015). The C-terminal region of MCAK controls its activity and structure through a major conformational switch. Elife.