Kinetochore oscillations in mitotic metaphase
Final Report Abstract
During metaphase, sister chromatids are connected to microtubules extending from the opposite spindle poles via kinetochores, protein complexes on the chromosome. Kinetochores congress to the spindle equatorial plane and oscillate around it, with kinesin-8 motors restricting these movements. Yet, the physical mechanism underlying kinetochore movements is unclear. We show that kinetochore movements in the fission yeast Schizosaccharomyces pombe are regulated by kinesin-8-promoted microtubule catastrophe, force-induced rescue and microtubule dynamic instability. A candidate screen showed that among the selected motors only kinesin-8 motors Klp5/Klp6 are required for kinetochore centering. Kinesin-8 accumulates at the end of microtubules, where it promotes catastrophe. Laser ablation of the spindle resulted in kinetochore movement towards the intact pole in wild-type and klp5Δ cells, suggesting that kinetochore movement is driven by pulling forces. Our theoretical model with Langevin description of microtubule dynamic instability shows that kinesin-8 motors are required for kinetochore centering, whereas sensitivity of rescue to force is necessary for the generation of oscillations. We found that irregular kinetochore movements occur for a broader range of parameters than regular oscillations. Thus, our work provides an explanation for how regulation of microtubule dynamic instability contributes to kinetochore congression and the accompanying movements around the spindle center. Our work was highlighted on the cover page of Molecular Biology of the Cell. On the cover: During metaphase, sister chromatids are connected to microtubules extending from the opposite spindle poles via kinetochores, protein complexes on the chromosome. This mosaic of kymographs, where microtubules are shown in green and kinetochores in magenta, displays how kinetochores congress to the spindle center and oscillate around it during metaphase, before moving to the opposite spindle poles during anaphase. Yet, the physical mechanism underlying kinetochore movements is unclear. Klemm et al. show how kinesin-8 motors and microtubule dynamic instability regulate kinetochore movements.
Publications
- Kinesin-8 motors improve nuclear centering by promoting microtubule catastrophe. Phys. Rev. Lett. 114(7): 078103 (2015)
M. Glunčić, N. Maghelli, A. Krull, V. Krstić, D. Ramunno-Johnson, N. Pavin, and I.M. Tolić
(See online at https://doi.org/10.1103/PhysRevLett.114.078103) - Microtubule sliding within the bridging fiber pushes kinetochore fibers apart to segregate chromosomes. Dev. Cell. 43: 11-23 (2017)
K. Vukušić, R. Buđa, A. Bosilj, A. Milas, N. Pavin, and I.M. Tolić
(See online at https://doi.org/10.1016/j.devcel.2017.09.010) - Metaphase kinetochore movements are regulated by kinesin-8 motors and microtubule dynamic instability. Mol. Biol. Cell. 29: 1332-1345 (2018)
A.H. Klemm, A. Bosilj, M. Glunčić, N. Pavin, and I.M. Tolić
(See online at https://doi.org/10.1091/mbc.E17-11-0667)
