Chromosome biorientation requires Aurora B's spatial separation from its outer kinetochore substrates but not its turnover at kinetochores

Abstract

For correct chromosome segregation in mitosis, sister kinetochores must interact with microtubules from opposite spindle poles (biorientation). For this, aberrant kinetochore- microtubule interaction must be resolved (error correction) by Aurora B kinase. Once biorientation is formed, tension is applied across sister kinetochores, stabilizing kinetochore- microtubule interactions. The mechanism for this tension-dependent process has been debated. Here we study how localizations of Aurora B at different kinetochore sites affect the establishment and maintenance of biorientation in budding yeast. In the absence of the physiological Aurora B-INCENP recruitment mechanisms, engineered recruitment of Aurora B-INCENP to the inner kinetochore (Mif2) prior to biorientation supports the subsequent establishment of biorientation. By contrast, an engineered Aurora B-INCENP recruitment to the outer kinetochore (Ndc80) fails to support biorientation establishment. Furthermore, when the physiological Aurora B-INCENP recruitment mechanisms are present, an engineered Aurora B-INCENP recruitment to Mif2 during metaphase (after biorientation establishment) does not affect biorientation maintenance. By contrast, an engineered Aurora B-INCENP recruitment to Ndc80 during metaphase leads to disruption of biorientation, which is dependent on the kinase activity of Aurora B. Taken together, our results suggest that spatial separation of Aurora B from its outer kinetochore substrates is required to stabilize kinetochore-microtubule interaction when biorientation is formed and tension is applied on this interaction. Meanwhile, Aurora B shows dynamic turnover (or exchange) on the centromere and kinetochore during early mitosis. It has been thought that this turnover is crucial for error correction and biorientation, as it may help Aurora B reach its substrates in distance and/or may facilitate the Aurora B activation on the mitotic spindle. However, using the engineered Aurora B-INCENP recruitment to the inner kinetochore, we demonstrate that, even without such a turnover, Aurora B-INCENP can efficiently support biorientation. Altogether, our study provides important insights into how Aurora B promotes error correction and biorientation in a tension-dependent manner.