Characterization of a microtubule assembly inhibitor from Xenopus oocytes

The dynamic properties of microtubules (MTs) are important for a wide varie ty of cellular processes, including cell division and morphogenesis. MT ass embly and disassembly in vivo are regulated by cellular factors that influe nce specific parameters of MT dynamics. Here, we describe the characterizat ion of a previously reported MT assembly inhibitor activity from Xenopus oo cytes [Gard and Kirschner, 1987: J. Cell Biol. 105.2191-2201]. Video micros copy measurements reveal that the inhibitor specifically decreases the plus end growth rate of MTs and increases the critical concentration for tubuli n. However, catastrophe frequency, rescue frequency, and shrinkage rates ar e not affected by the activity. Chromatography on Mono Q and hydroxyapatite columns has shown that the activity cofractionates with a subpopulation of tubulin. This tubulin subpopulation and the MT assembly inhibitor activity also co-migrate with a large S value (25-308) on sucrose gradients. The hi gh molecular weight tubulin complex and the MT assembly inhibitor activity are both developmentally regulated and disappear after oocyte maturation wi th progesterone. Cell Motil. Cytoskeleton 45.51-57, 2000. (C) 2000 Wiley-Li ss, Inc.