The Role Of Kinetochore Protein Mitosin In Mitosis

Mitosin (also named CENP-F) is a large human nuclear protein transiently associated with the outer kinetochore plate in M phase. Previous studies have well defined its character and implied it involves in M phase progression. However, the role of mitosin remains elusive. In this study, we firstly confirmed mitosin is also a kinetochore protein in primary cell and its mammalian orthologs also localize at kinetochore. Next we try to reveal the function of mitosin in mitosis. Using RNA interference, confocal microscopy, and live cell imaging, we showed that mitosin depletion attenuated chromosome congression and led to metaphase arrest with misaligned polar chromosomes whose kinetochores showed little cold-stable microtubules. Kinetochores of fully aligned chromosomes often failed to show orientations in the direction of the spindle long axis. Moreover, tension across their sister kinetochores was decreased by 53% on average. These phenotypes collectively imply defects in motor functions in mitosin-depleted cells and are similar to those of CENP-E depletion. Consistently, intensities of CENP-E and cytoplasmic dynein/dynactin, which are motors controlling microtubule attachment and chromosome movement, were reduced at the kinetochore in microtubule-dependent manners. In addition, after being arrested in pseudometaphase for approximately 2 hr, mitosin-depleted cells died before anaphase initiation through apoptosis. The dying cells exhibited progressive chromosome arm decondensation while the kinetochores were still associated with spindles. We also noticed that less than 20% mitosin-depleted cells entered metaphase with all chromosome aligned at equator plate. Some of these cells cannot enter anaphase and died after chromosome decondensation. Some can enter anaphase, however, they cannot segregate sister...