The overarching goal of this proposal is to establish the mechanisms responsible for proper segregation of chromosomes during cell division. High vs. low fidelity of chromosome segregation is a characteristic difference between normal vs. cancer cells and understanding the mechanisms responsible for this difference is an essential step towards developing novel anti-cancer therapeutics and treatments strategies. For proper segregation, each chromosome must attach to the microtubules of mitotic apparatus (termed the 'spindle') and this attachment is mediated by special macromolecular assemblies on the chromosome's body known as the 'kinetochores'. The project is enabled by recent demonstrations that geometric constraints of microtubule/kinetochore interactions play a vital role in ensuring proper formation of the mitotic spindle essential for faithful chromosome segregation. These geometric constraints are established by the distribution and orientation of molecular complexes within the kinetochore and this project is designed to reveal how the architecture of the kinetochore, and the orientation of individual molecular complexes within that architecture, adapt to rapidly changing conditions within the mitotic spindle.
We aim to dissect the nature of structural reorganizations known to occur within the kinetochore during different stages of mitosis and different physiological states of the kinetochore. To achieve these goals we use a unique approach in which high- resolution electron-microscopy analyses are conducted on the kinetochores whose behavior and movements were followed in live cells up to the moment of fixation. This approach, termed correlative LM/EM allows us evaluate the structure of kinetochores that are in known functional state thus revealing the exact structural changes that occur during transitions between various physiological states. We will also perform comparative structural analyses of kinetochores upon two functionally-characterized experimental conditions: 1) treatment with low concentration of taxol, a condition known to allow satisfaction of the mitotic checkpoint despite the lack of centromere tension vs. 2) treatment with low concentration of nocodazole, a condition known to prevent satisfaction of the SAC despite highly-stretched centromeres. Together, these studies will allow us to create an accurate model for the structure of the kinetochore and determine how the architecture and the distribution of molecular components within the kinetochore adapt in response to various types of microtubule attachment and various types of chromosome movements.

Public Health Relevance

This project aims to reveal the mechanisms that ensure proper segregation of chromosomes during cell division (mitosis). We use sophisticated light and electron microscopy to investigate how molecular architecture of the kinetochore, an organelle that attaches chromosomes to the spindle microtubules, adapts to various types of microtubule attachment and various types of chromosome movements. Detailed understanding of these adaptations is essential for finding new means to prevent or repair problems in chromosome segregation that are a hallmark feature of cancer.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Special Emphasis Panel (ZGM1-CBB-0 (MI))
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Gindhart, Joseph G
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Wadsworth Center
United States
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Magidson, Valentin; He, Jie; Ault, Jeffrey G et al. (2016) Unattached kinetochores rather than intrakinetochore tension arrest mitosis in taxol-treated cells. J Cell Biol 212:307-19
Tikhonenko, Irina; Irizarry, Karen; Khodjakov, Alexey et al. (2016) Organization of microtubule assemblies in Dictyostelium syncytia depends on the microtubule crosslinker, Ase1. Cell Mol Life Sci 73:859-68
Magidson, Valentin; Paul, Raja; Yang, Nachen et al. (2015) Adaptive changes in the kinetochore architecture facilitate proper spindle assembly. Nat Cell Biol 17:1134-44
Atilgan, Erdinc; Magidson, Valentin; Khodjakov, Alexey et al. (2015) Morphogenesis of the Fission Yeast Cell through Cell Wall Expansion. Curr Biol 25:2150-7
Heald, Rebecca; Khodjakov, Alexey (2015) Thirty years of search and capture: The complex simplicity of mitotic spindle assembly. J Cell Biol 211:1103-11
Sikirzhytski, Vitali; Magidson, Valentin; Steinman, Jonathan B et al. (2014) Direct kinetochore-spindle pole connections are not required for chromosome segregation. J Cell Biol 206:231-43
Magidson, Valentin; Khodjakov, Alexey (2013) Circumventing photodamage in live-cell microscopy. Methods Cell Biol 114:545-60
Tikhonenko, Irina; Magidson, Valentin; Graf, Ralph et al. (2013) A kinesin-mediated mechanism that couples centrosomes to nuclei. Cell Mol Life Sci 70:1285-96
Schilling, Z; Frank, E; Magidson, V et al. (2012) Predictive-focus illumination for reducing photodamage in live-cell microscopy. J Microsc 246:160-7
Leo, Meredith; Santino, Diana; Tikhonenko, Irina et al. (2012) Rules of engagement: centrosome-nuclear connections in a closed mitotic system. Biol Open 1:1111-7

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