Mitosis is a highly-regulated process that ensures the accurate segregation of chromosomes to create genetically identical daughter cells. One of the most conspicuous features of mitosis is the compaction of genetic material into discrete chromosomes. Chromosome compaction is performed, in part, by Condensin complexes and is thought to facilitate the movement needed for unobstructed chromosome alignment and segregation. However, the influence of compaction on chromosome movement in mitosis is unclear. To explore this question, we used live cell imaging to track chromosome movement in cells depleted of the essential Condensing II subunit CAP-D3. Chromosomes in cells depleted of CAP-D3 aligned at the spindle equator, but did not display typical periodic oscillatory movement. Some chromosomes appeared stationary whereas others showed erratic motion including uncoupling of sister kinetochores. CAP- D3 depletion had no detectable effect on the localization or function of the kinesin Kif18A. However, it did disrupt the loading of chromokinesins Kid and Kif4A onto chromosomes. Correspondingly, the influence that both motors have on polar ejection force was lost. Thus, Condensins promote the association of chromokinesins with mitotic chromatin to influence chromosome movement in mitosis.

While depletion of Condensins yields chromatin that is more relaxed, we also set out to look at the opposite effect. Inhibition of topoisomerase II leaves sister chromatids more closely tangled together. We did observe changes in the composition of centromeres when topoisomerase II was inhibited. However, the confounding problem of sister chromatids remaining tangled into anaphase makes analysis of how chromosomes are bound to microtubules difficult.

When chromosome segregation does go awry in mitosis and chromosomes are mis-segregated, aneuploid cells are produced. Normal cells arrest if they become aneuploid, but cancer cells do not and often benefit from aneuploidy. How cells are able to detect the gain or loss of a chromosome has not yet been determined. The second part of this thesis addresses one possible way in which cells could detect aneuploidy. The delicate balance of imprinted genes, which are only expressed from one allele based on the parent from which it was inherited, and ribosomal protein genes, which produce a vital stoichiometrically balanced complex, provided intriguing possibilities as sensors. However, the overexpression of one protein from each group did not yield a response in diploid RPE-1 cells that would mirror that seen in aneuploid cells.