Tension sensors reveal how the kinetochore shares its load.

At metaphase in mitotic cells, pulling forces at the kinetochore-microtubule interface create tension by stretching the centromeric chromatin between oppositely oriented sister kinetochores. This tension is important for stabilizing the end-on kinetochore microtubule attachment required for proper bi-orientation of sister chromosomes as well as for satisfaction of the Spindle Assembly Checkpoint and entry into anaphase. How force is coupled by proteins to kinetochore microtubules and resisted by centromere stretch is becoming better understood as many of the proteins involved have been identified. Recent application of genetically encoded fluorescent tension sensors within the mechanical linkage between the centromere and kinetochore microtubules are beginning to reveal - from live cell assays - protein specific contributions that are functionally important.