Graduate Thesis Or Dissertation
 

The impact of the number of kinetochore microtubules on the rate of chromosome segregation

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  • Successful cell division requires proper chromosome movement, including accurate congression to the metaphase plate and proper segregation to spindle poles. Errors that occur in either event can cause chromosome aneuploidy in daughter cells, which may lead to cell death, genetic diseases and cancers (Matson and Stukenberg,2012, Compton, 2000). The force powering chromosome movement is mainly generated by the polymerization and depolymerization of kinetochore microtubules, and their interaction with the attached molecular motor proteins (Barton and Goldstein, 1996). Microtubule dynamics and motor activities have been studied extensively to understand how they move chromosomes, yet there are many questions remain to be answered. Our goal is to understand the impact of kinetochore microtubule numbers on chromosome movement. We hypothesized that chromosome segregation to the spindle pole requires synchronized shorting of kinetochore microtubules that attach the chromosome to the pole. Therefore, a higher number of kinetochore microtubules in a kinetochore fiber leads to a lower rate of chromosome movement to the pole in anaphase. To test this hypothesis, we used micro-techniques to alter the number of microtubules at the kinetochore and measured its impact on the rate of chromosome segregation using polarization microscopy and computer-assisted tracking technology (Skibbens et al.,1993). We found that in single-chromosome cells created via micromanipulation, the chromosome captured more kinetochore microtubules but had slower rate of segregation than that of the control cells. If however, the chromosome failed to capture more kinetochore microtubules, it segregated at almost the same rate as that of the control cells. To minimize the potential impact of micromanipulation on the rate of chromosome segregation, we directly compared the segregation rates of homologues with altered number of kinetochore microtubules in the same cell. Again, the chromosome with more kinetochore microtubules always segregated slower than its homologue. We conclude that the rate of chromosome segregation in anaphase is inversely proportional to the number of kinetochore microtubules that attach the chromosome to the spindle pole.
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