The unusual polymerization behavior of microtubules known as dynamic instability is thought to play an important role in morphogenesis. The means by which this behavior is regulated in vivo is very poorly understood. Experiments are proposed to look at global regulation of microtubule stability in cells, and in particular to look at the effect of partial ATP depletion and microinjection of specific kinases and phosphatases. Additional proteins that show phosphorylation-dependent or ATP-dependent binding to microtubules in vitro will be sought, and the relationship of microtubule stability as measured by nocodazole sensitivity (the basis for almost all previous analyses), and stability, as measured by the incorporation of biotin-labelled tubulin, will be explored. Further studies are planned to determine whether stable microtubules in vivo are capped at their ends or inhibited from depolymerization by binding of proteins along the length of the polymer. The detailed mechanisms by which microtubule associated proteins and microtubule motor proteins contribute to microtubule stability will be explored by transfection and biotin-tubulin injection. In these experiments a study of the structure of specific microtubule-associated proteins will be combined with in vivo studies of physiological regulation of microtubules in the hope of understanding how the morphogenesis of microtubule arrays is generated. "Microtubules" are sub-microscopic structures, small tubes, within cells that serve as a component of the internal "skeleton" that determines a cell's shape. Microtubules also serve as tracks, along which other sub-cellular structures move. Microtubules are unstable structures that polymerize or depolymerize in response to changing physiological conditions within the cell. This US-USSR cooperative research involves two of the world's leading experts on microtubule structure and function in a study of the mechanisms that control microtubule stability. The results of this collaborative research should provide important new information concerning the biochemical factors that determine where, within cells, microtubules form, how many form, and what determines their length. This knowledge will be an important contribution to our fundamental understanding of how cells function.
