MECHANISM AND REGULATION OF MICROTUBULE TURNOVER

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Microtubules are dynamic structures that are required for several vital processes in eukaryotic cells including mitosis, the establishment and maintenance of cell shape and cell motility. The overall objective of our work is to determine the mechanism(s) by which microtubules are remodelled as cells traverse the cell cycle and locomote and how microtubules contribute to efficient cellular motility. A key feature of our experimental approach is the analysis of microtubules in the living cell. To accomplish this we will use quantitative digital fluorescence microscopy, photoactivation of caged tubulin, fluorescence analog cytochemistry and photobleaching of GFP- tagged proteins. The major aims are to determine the dynamic properties of the minus-ends of centrosomal microtubules; measure nucleation and release of centrosomal microtubules in motile and non-motile cells; determine the mechanism responsible for microtubule transport; determine if centrosome reorientation occurs during motion of fibroblast-like cells and during cell migration into a wounded monolayer; and determine the regulatory pathways that govern microtubule turnover in motile cells. Microtubule dynamics and remodelling will be studied in highly motile keratocytes and in two model systems for mammalian cell motility: migration into a wound and fibroblast-like motion in response to growth factors. The results will elucidate the mechanisms of microtubule turnover in live cells and contribute to our understanding of the role of microtubules in cell polarity and motility. Understanding these processes in normal cells is an important first step towards analysis of cancer cells, where such processes are aberrant.