Microtubule Dynamics during the Cell Cycle: The Effects of Taxol and Nocodazole on the Microtubule System of Pt K2 Cells at Different Stages of the Mitotic Cycle

Abstract

Nocodazole is a rapidly penetrating and easily reversible microtubule (MT) assembly inhibitor that allows a closer approach to real in vivo dynamics during the cell cycle. Taxol, a diterpenoid isolated from Taxus brevifolia, has rapidly gained a unique position as an experimental tool in the field of microtubule research. It is the first and the only low-molecular-weight compound (except for ubiquitous, endogenous cofactors such as GTP) that promotes microtubule assembly in vitro. It inhibits the subunit dissociation rate constants identically at both ends of microtubules without any apparent effect on the association rate constants. The effects of taxol on living cells of various origins (mammals, plants, sea urchin eggs, protozoa) were invariably related to alterations in the MT system. The changes induced depend on the cell type, the concentration of taxol, and the treatment time. This chapter describes the immediate and late alterations induced by taxol added at different stages of the cell cycle to marsupial (Pt K2) cells in culture. The effects of a complete dose range, from inactive concentrations to those at the limit of solubility are presented in this chapter. The chapter also explains how the drug alters neoformation of microtubules in cells pretreated with nocodazole, with and without removal of the latter before addition of taxol. In addition, the implications of the alterations in the MT system for various aspects of cell polarity, organization, and motility are described. The chapter also describes the present state of the art by proposing a biased view of microtubule assembly throughout the mitotic cycle.