| Successful cell division requires the equal segregation of the replicated genome. This process is carried out by a cellular machine known as the mitotic spindle, which is largely conserved across eukaryotes. I have used the budding yeast Saccharomyces cerevisiae as a model organism to better understand the mechanics of the mitotic spindle and the mechanisms that coordinate events during mitosis.; Prior to segregation, sister chromatids form bi-polar attachments to microtubules nucleated from the two spindle pole bodies. These attachments are mediated by the kinetochores which link centromeric DNA to microtubules. Biorientation of sister chromatids results in their alignment at the spindle equator, a state known as metaphase. During metaphase, spindle length remains stable. This stability has been largely attributed to the activity of microtubule motors in the spindle. I have taken an alternative approach to dissecting the forces within the metaphase spindle by examining the role of chromatin structure of sister chromatids. By lowering chromatin packaging, I have shown that spindle length is directly regulated by the stretching of pericentric chromatin. This result demonstrates that chromatin is an important structural member of the metaphase spindle.; Following metaphase, chromosomes segregate and the cell undergoes cell division to produce two daughter cells. I found that during anaphase, a fraction of inner kinetochore proteins re-localizes to the spindle midzone. This re-localization requires the activity of a yet unidentified motor. Mutation of the inner kinetochore protein Ndc10p results in defects in spindle stability and cell division. This mechanism of spatial regulation of kinetochore proteins appears to contribute to the coordination of chromosome segregation, spindle elongation, and cell division. |
