Chromosome size-dependent polar ejection force impairs mammalian mitotic error correction

Summary of the work: Accurate chromosome segregation requires sister kinetochores to biorient, attaching to opposite spindle poles. To this end, the mammalian kinetochore destabilizes incorrect attachments and stabilizes correct ones, but how it discriminates between these is not yet clear. Here, we test the model that kinetochore tension is the stabilizing cue and ask how chromosome size impacts that model. We live image PtK2 cells, with just 14 chromosomes, widely ranging in size, and find that long chromosomes align at the metaphase plate later than short chromosomes. Enriching for errors and imaging error correction live, we show that long chromosomes exhibit a specific delay in correcting attachments. Using chromokinesin overexpression and laser ablation to perturb polar ejection forces, we find that chromosome size and force on arms determine alignment order. Thus, we propose a model where increased force on long chromosomes can falsely stabilize incorrect attachments, delaying their biorientation. As such, long chromosomes may require compensatory mechanisms for correcting errors to avoid chromosomal instability. Data associated with the paper: "Chromosome size-dependent polar ejection force impairs mammalian mitotic error correction" Chong et al. Journal of Cell Biology. (doi: 10.1083/jcb.202310010) Here, we include data used to generate the figures in this paper. Files are created and can be opened with GraphPad Prism. Individual kinetochore position data used to generate average distance to pole and average speed in monopolar spindles for control (Fig. 1H, Fig. 2E) and chromokinesin overexpression (Fig. S3) can be found in the excel file titled "distance to pole source data".