Cell division: righting the check

Abstract

Studies in fission and budding yeast have continuously led the way for analyzing pathways of cell division. Two elegant studies, one from each yeast species, are opening the gates to study one of the final steps of mitosis--silencing the spindle checkpoint.

Figure 1. PP1 contributes to SAC regulation at kinetochores

(A) In the unattached state, SAC proteins are enriched at kinetochores that are in close proximity to the inner centromere and (Au: OK?) amplify the SAC signal from Aurora B kinase. Kinase signaling predominates over PP1 opposition, and both tension and occupancy branches of the SAC are active. (B) Upon microtubule attachment, some but not all SAC proteins are displaced, resulting in a greater dependence on Aurora kinase activity to maintain the SAC signal in the presence of opposition by PP1. The occupancy branch is silenced and the tension branch remains active. (C) When kinetochores come under tension, they are physically displaced from the inner centromere, allowing PP1 activity to dominate. SAC complexes no longer reside at the kinetochore and both tension and occupancy branches are silenced. Syntelic attacment: sister kinetochores attached to the same spindle pole; Amphitelic attachment: sister kinetochores attached to opposite poles (bipolar attachment).