Mitosis is the process by which a replicated set of chromosomes is equally distributed between two daughter cells. Because cells require a complete genetic blueprint to function properly, it is essential for mitosis to occur without error mis-segregation of even a single chromosome can be the cause of genetic disease, cancer, and death. Chromosomes are segregated by a microtubule-based cellular machine termed the spindle. A key feature of the spindle is its bipolar geometry, an organization that naturally allow chromosomes to be segregated in two directions. Other organizational states, such as monopolarity or multipolarity, are largely incompatible with life and cause cell death via apoptosis. This renewal application is focused on how spindle bipolarity is both established and maintained. Spindle bipolarity in most eukaryotic cells is established by Eg5, a kinesin-5 motor. However, we discovered in the previous grant cycle that bipolarity in human cancer cells can be established through a novel Eg5-indpendent mechanism. This finding has important clinical implications, as kinesin-5 inhibitors (K5Is) have not performed well as anti-cancer agents in early stage clinical trials. Our work suggests that the inefficacy of K5Is may stem from alternative, compensatory spindle assembly pathways. Once the spindle has formed, it must remain bipolar despite the presence of forces that act in opposition to Eg5. The source, magnitude and temporal fluctuations of Eg5-opposing/assisting forces are not well-characterized, but our data implicate the involvement of kinetochore-attached microtubules (K- MTs). In this grant, we will: 1) Determine when and how K-MTs contribute to bipolarity maintenance; 2) Study features of a second kinesin (Kif15) key for Eg5-independent spindle assembly; and 3) Further characterize non-canonical spindle assembly mechanisms and their physiological shortcomings. This work will advance our understanding of spindle mechanics and have immediate relevance to the development of anti-mitotic chemotherapeutic strategies.

Public Health Relevance

Bipolarity is an essential feature of the mitotic spindle, a microtubule-based machine that segregates a replicated set of chromosomes among two daughter cells during mitosis. Spindle bipolarity is established and maintained by forces from ill-defined sources that ultimately position centrosomes at opposite ends of a dividing cell. In this application, we will: 1) Determine when and how K-MTs enforce bipolarity maintenance; and 2) Study non-canonical, Eg5-independent mechanisms that establish spindle bipolarity.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
7R01GM086610-08
Application #
9589090
Study Section
Nuclear and Cytoplasmic Structure/Function and Dynamics Study Section (NCSD)
Program Officer
Gindhart, Joseph G
Project Start
2010-05-01
Project End
2020-04-30
Budget Start
2017-09-01
Budget End
2018-04-30
Support Year
8
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
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Sturgill, Emma G; Das, Dibyendu Kumar; Takizawa, Yoshimasa et al. (2014) Kinesin-12 Kif15 targets kinetochore fibers through an intrinsic two-step mechanism. Curr Biol 24:2307-13
Gayek, A Sophia; Ohi, Ryoma (2014) Kinetochore-microtubule stability governs the metaphase requirement for Eg5. Mol Biol Cell 25:2051-60

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