Regulation of the localization and activity of Mps1 kinase at the kinetochore

Abstract

Every time a cell divides, chromosomes must be segregated accurately between daughter cells. Chromosome segregation defects are a hallmark of several major diseases that threaten human health, including cancer and infertility. To be segregated, chromosomes must make and maintain bioriented attachments to dynamic microtubules of a bipolar spindle that forms in dividing cells. The kinetochore is the protein complex that attaches chromosomes to microtubules and it serves as a platform for multiple signaling pathways that promote accurate segregation. The essential protein kinase Mps1 promotes biorientation through multiple mechanisms, however the mechanism by which it associates with kinetochores to carry out these processes is unclear. To address this, I, along with my collaborators, performed reconstitution experiments with kinetochore complexes purified from budding yeast. We found that kinetochore-microtubule attachment did not displace Mps1 bound to kinetochores, as has been proposed. Instead, I showed that autophosphorylation triggers Mps1 release and prevents re-binding to kinetochores. In addition, I investigated whether Mps1 phosphorylation of kinetochores directly regulates kinetochore-microtubule attachments. I found that Mps1 phosphorylation weakens reconstituted kinetochore-microtubule attachments. I also provide evidence that Mps1 phosphorylation of microtubule-binding components of the kinetochore is required for accurate chromosome segregation in cells. My work elucidates critical mechanisms of Mps1 kinase regulation in budding yeast and future work should address whether such mechanisms are conserved in other organisms.