Kinetochore alignment within the metaphase plate is regulated by centromere stiffness and microtubule depolymerases.

During mitosis in most eukaryotic cells, chromosomes align and form a metaphase plate halfway between the spindle poles, about which they exhibit oscillatory movement. These movements are accompanied by changes in the distance between sister kinetochores, commonly referred to as breathing. We developed a live cell imaging assay combined with computational image analysis to quantify the properties and dynamics of sister kinetochores in three dimensions.

Kinetochore-generated pushing forces separate centrosomes during bipolar spindle assembly.

In animal somatic cells, bipolar spindle formation requires separation of the centrosome-based spindle poles. Centrosome separation relies on multiple pathways, including cortical forces and antiparallel microtubule (MT) sliding, which are two activities controlled by the protein kinase aurora A. We previously found that depletion of the human kinetochore protein Mcm21R(CENP-O) results in monopolar spindles, raising the question as to whether kinetochores contribute to centrosome separation.

The CENP-A NAC/CAD kinetochore complex controls chromosome congression and spindle bipolarity.

Kinetochores are complex protein machines that link chromosomes to spindle microtubules and contain a structural core composed of two conserved protein-protein interaction networks: the well-characterized KMN (KNL1/MIND/NDC80) and the recently identified CENP-A NAC/CAD. Here we show that the CENP-A NAC/CAD subunits can be assigned to one of two different functional classes; depletion of Class I proteins (Mcm21R(CENP-O) and Fta1R(CENP-L)) causes a failure in bipolar spindle assembly. In contrast, depletion of Class II proteins (CENP-H, Chl4R(CENP-N), CENP-I and Sim4R(CENP-K)) prevents binding of Class I proteins and causes chromosome congression defects, but does not perturb spindle formation.