Dynamic instability of microtubules: effect of catastrophe-suppressing drugs

Microtubules are stiff filamentary proteins that constitute an important component of the cytoskeleton of cells. These are known to exhibit a dynamic instability. A steadily growing microtubule can suddenly start depolymerizing very rapidly; this phenomenon is known as ``catastrophe''. However, often a shrinking microtubule is ``rescued'' and starts polymerizing again. Here we develope a model for the polymerization-depolymerization dynamics of microtubules in the presence of {\it catastrophe-suppressing drugs}. Solving the dynamical equations in the steady-state, we derive exact analytical expressions for the length distributions of the microtubules tipped with drug-bound tubulin subunits as well as those of the microtubules, in the growing and shrinking phases, tipped with drug-free pure tubulin subunits. We also examine the stability of the steady-state solutions.Comment: Minor corrections; final published versio

A Polarised Population of Dynamic Microtubules Mediates Homeostatic Length Control in Animal Cells

An analysis of cells grown on micro-patterned lines, and of cells during zebrafish development, identifies a population of microtubules that align along the long axis of cells to mediate homeostatic length control

Effects of the Tubulin-Colchicine Complex on Microtubule Dynamic Instability

Original article can be found at: http://pubs.acs.org/journals/bichaw/index.html Copyright American Chemical Society DOI: 10.1021/bi00176a007 [Full text of this article is not available in the UHRA]The effects of the tubulin-olchicine complex (Tu-Col) on the dynamic behavior of microtubules have been examined under steady-state conditions in vitro. The addition of Tu-Col to tubulin microtubules at steady state results in only partial microtubule disassembly. Nevertheless, both the rate and the extent of tubulin exchange into microtubules are markedly suppressed by concentrations of Tu-Col which are low relative to the total amount of free tubulin. In addition, the time-dependent changes in microtubule length distribution, characteristic of dynamic instability, are suppressed by the addition of Tu-Col. Examination by video-enhanced dark-field microscopy of individual microtubules in the presence of Tu-Col shows that the principal effect of this complex is to reduce the growth rate at both ends of the microtubule. We have used computer simulation to rationalize the action of Tu-Col in terms of its effects on the experimentally observable parameters, namely, the rates of growth and shortening and the mean lifetimes of growth and shortening, which provide an empirical description of the dynamic behavior of microtubules. The results have been interpreted within the framework of the lateral cap formulation for microtubule dynamic instability [Martin, S. R., Schilstra, M. J., & Bayley, P. M. (1993) Biophys. J. 65, 578-5961, The simplest model mechanism requires only that Tu-Col binds to the microtubule end and inhibits further addition reactions in either the 5-start or the %start direction of the microtubule lattice. Monte Carlo simulations show that Tu-Col can, in this way, cause major suppression of the dynamic transitions of microtubules without inducing bulk microtubule disassembly. This type of mechanism could be important for the regulation of microtubule dynamics in vivo.Peer reviewe

Phaeobacter caeruleus sp nov., a blue-coloured, colony-forming bacterium isolated from a marine electroactive biofilm

Three isolates (LMG 24369(T), LMG 24370 and R-26156) obtained from a marine electroactive biofilm that was grown on a cathodically polarized electrode were investigated by using a polyphasic taxonomic approach. Whole-cell fatty acid methyl ester and 16S rRNA gene sequence analyses indicated that the isolates were members of the genus Phaeobacter, class Alphaproteobacteria. Genotypic and phenotypic analyses demonstrated that the three isolates represent a novel species of the genus Phaeobacter, for which the name Phaeobacter caeruleus sp. nov. is proposed. The type strain is LMG 24369(T) (=CCUG 55859(T)). The DNA G + C content of strain LMG 24369(T) is 63.6 mol%