Mechanisms for building and remodeling microtubule arrays

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Project Summary Control of the internal organization of cells is essential to the form and function of all organisms. This ability rests largely on an intricate protein filament network called the cytoskeleton which serves as a scaffolding structure to pattern cellular contents in space and time. Unlike human-made scaffolding structures, the cytoskeleton is highly dynamic and is able to change its configuration in response to developmental and environmental signals, allowing cells to adapt to changing conditions. Thus, the cytoskeleton is like an ever- changing structural “diagram”, and the goal of my research program is to understand how these diagrams are generated to execute essential cellular activities that underlie growth, development and physiology. Our research focuses on mechanisms for the creation, maintenance and restructuring of the microtubule cytoskeleton using the cortical microtubule array of Arabidopsis thaliana as an experimentally tractable system. We use a multidisciplinary approach and benefit from an extensive network of close collaborators with whom we freely share reagents and ideas. These advantages have allowed us to address previously intractable questions about cytoskeleton structure and function. Here, we will build on our recent progress to focus on four major goals: Goal 1) characterize new regulatory mechanisms that specifically tune the microtubule severing activity of katanin to uncover how various internal and external signals influence the assembly and disassembly of diverse microtubule structures through katanin. Goal 2) elucidate the structural dynamics that determine the functional diversity of MAP65 microtubule crosslinking proteins to gain insight into how evolution selected particular MAP65 sequences for specialized functions and to enable the creation of new tools to manipulate microtubule function in plants and animals. Goal 3) uncover the structure and mechanism of action of a new class of microtubule minus-end regulators to understand how TOG domains, which are typically associated with microtubule plus-end tracking proteins, have been repurposed to recognize and stabilize microtubule minus-ends. Goal 4) develop a new microfluidics chip platform to analyze the complex relationships between sets of microtubule regulatory proteins to obtain a clear and integrated picture of how concurrent molecular activities dynamically pattern microtubule structures. Together, these synergistic projects will provide a mechanistically detailed picture of the inner workings of complex microtubule structures and advance our understanding of their functions in cell biology and disease.