Centrosomes control kinetochore-fiber plus-end dynamics via HURP to ensure symmetric divisions

Abstract

During mitosis centrosomes can affect the length of kinetochore-fibers (k-fibers) and the stability of kinetochore-microtubule attachments, implying that they regulate k-fiber dynamics. The exact cellular and molecular mechanisms by which centrosomes regulate k-fibers remain, however, unknown. Here, we created human non-cancerous cells with only one centrosome to investigate these mechanisms. Such cells formed highly asymmetric bipolar spindles that resulted in asymmetric cell divisions. K-fibers in acentrosomal spindles were shorter, more stable, had a reduced poleward microtubule flux at minus-ends, and more frequent pausing events at their plus-ends. This indicates that centrosomes regulate k-fiber dynamics both locally at minus-ends and far away at plus-ends. At the molecular level we find that the microtubule-stabilizing protein HURP is enriched on the k-fiber plus-ends in the acentrosomal spindles of cells with only one centrosome. HURP depletion rebalance k-fiber stability and dynamics in such cells, and improved spindle and cell division symmetry. Our data further indicate that HURP accumulates on k-fibers inversely proportionally to half-spindle length. We propose that centrosomes regulate k-fiber plus-ends indirectly via length-dependent accumulation of HURP. Thus by ensuring equal k-fiber length, centrosomes promote HURP symmetry, reinforcing the symmetry of the mitotic spindle and of cell division.