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

Chromosome segregation during mitosis depends on accurate kinetochore attachments. It was already known that sister kinetochores must biorient to ensure proper segregation. However, the mechanisms that allow kinetochores to distinguish between correct and incorrect attachments remain unclear. One proposed model suggests that tension at the kinetochore is a key stabilizing cue. This gap motivated researchers to investigate how chromosome size might influence this model. Prior research has shown that larger chromosomes may face unique challenges during alignment. No prior work had resolved how polar ejection forces interact with chromosome size. This uncertainty drove the current study to explore the role of polar ejection forces in error correction. Understanding these forces could help clarify how mammalian cells maintain genomic stability.

This study aimed to test the hypothesis that kinetochore tension is the primary cue for stabilizing correct attachments. The researchers focused on how chromosome size affects this process. They used PtK2 cells, which have a small number of chromosomes with varying sizes. The goal was to determine if larger chromosomes align later than smaller ones. They also sought to understand how long chromosomes handle error correction. By observing live cells, they could track alignment and correction dynamics. The study aimed to clarify whether polar ejection forces influence these processes. The results could help explain how chromosome size impacts mitotic accuracy.

The researchers used live-cell imaging to observe PtK2 cells during mitosis. They selected PtK2 cells due to their limited and variable chromosome count. They enriched for cells with attachment errors to study correction mechanisms. Chromokinesin overexpression was used to manipulate polar ejection forces. Laser ablation allowed them to directly perturb these forces. They tracked the timing of chromosome alignment at the metaphase plate. Long and short chromosomes were compared for alignment order. The methods combined imaging with physical perturbations to test the model.

Long chromosomes aligned at the metaphase plate later than short chromosomes. Error correction was delayed in long chromosomes compared to short ones. Chromokinesin overexpression altered polar ejection forces in predictable ways. Laser ablation confirmed that these forces influence alignment order. The force on chromosome arms was found to correlate with alignment timing. Long chromosomes experienced greater polar ejection forces. These forces may falsely stabilize incorrect attachments in long chromosomes. The results support a model where size-dependent forces affect error correction.

The findings suggest that polar ejection forces vary with chromosome size. These forces may falsely stabilize incorrect attachments in long chromosomes. Delayed error correction in long chromosomes could lead to chromosomal instability. The study supports a model where size influences mitotic accuracy. The results do not confirm the necessity of any specific mechanism. The authors propose that compensatory mechanisms may be required for long chromosomes. The study does not claim to resolve all aspects of error correction. The findings may help explain how chromosome size affects mitotic outcomes.