Mechanisms of Mitotic Fidelity

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Project Summary The major goal of mitosis is to distribute the genetic material accurately between two daughter cells. Defects in meiosis or mitosis lead to aneuploidy, which is a significant cause of birth defects and is a hallmark of tumorigenesis. Critical to this process is the mitotic spindle, which is a cellular macromolecular machine tasked with both alignment and segregation of the genetic material. Even though the spindle structure and molecular players are highly conserved across organisms, the detailed organization of the spindle and protein function can vary even between cell types within an organism. This variation suggests that cells have evolved multiple pathways to ensure the proper distribution of genetic material. My lab has a long-standing interest in understanding how molecular motor proteins organize spindle structure, regulate microtubule dynamics in the spindle, and contribute to accurate chromosome segregation during mitosis. These studies are important because motor proteins not only play fundamental roles in spindle organization and function, but also because they are often overexpressed in cancer cells and may be valuable targets for therapeutic development. In the next five years, our studies will focus on three key questions. 1) How is molecular motor activity spatially and temporally regulated? An important goal is to understand not only how molecular motors function individually, but also how groups of motors cooperate with their binding partner to regulate spindle function. Our studies will define critical networks between biochemical activities of motors and cellular readouts of that activity. 2) How do regulated microtubule dynamics and centrosome clustering enhance mitotic fidelity? The current model is that cancer cells generate low levels of aneuploidy to drive their survival while limiting severe aneuploidy that would ensure cell death. We will uncover how key molecular motors impact mitotic fidelity by dissecting their function in mitosis and DNA damage repair. In addition, we will examine how centrosome clustering restricts severe aneuploidy in cells with amplified centrosomes. 3) How is accurate chromosome segregation impacted by increased chromosome load in cells with altered ploidy? An important but understudied problem is to elucidate how the normal complement of cellular proteins handles aneuploidy in both normal and cancer cells and how changes in the relative expression levels of key players impact accurate segregation of the genetic material. We will take advantage of our ability to generate cells with different levels of ploidy to understand how changing expression of key molecular motors is impacted by increased chromosome load and how that affects mitotic fidelity. Our proposed studies take advantage of our toolbox of key molecules, rigorous biochemical assays, high quality imaging, and diverse model systems to define the function of motors and regulatory networks that control mitotic fidelity. The outcome of these studies will define mechanisms by which distinct protein-protein interaction networks impact spindle morphogenesis and will provide new insights into how cells maintain genome integrity.