Three-dimensional microtubule behaviour in Xenopus egg extracts reveals four dynamic states and state-dependent elastic properties
Philipp J Keller 1*, Francesco Pampaloni 1, Gianluca Lattanzi 2 and Ernst HK Stelzer 1
1 European Molecular Biology Laboratory (EMBL)
2 University of Bari
* To whom correspondence should be addressed. E-mail: keller{at}embl.de.
Submitted on December 21, 2007
Revised on February 13, 2008
Accepted on 3 April 2008
 |
Abstract |
|---|
Although microtubules are key players in many cellular processes (1), very little is known about their dynamic and mechanical properties in physiological three-dimensional environments. The conventional model of microtubule dynamic instability postulates two dynamic microtubule states (2,3), growth and shrinkage. However, several studies have indicated that such a model does not provide a comprehensive quantitative and qualitative description of microtubule behaviour (4-6). Using three-dimensional laser light-sheet fluorescence microscopy (7,8) and a three-dimensional sample preparation in spacious Teflon cylinders (6), we measured microtubule dynamic instability and elasticity in interphase Xenopus laevis egg extracts. Our data are inconsistent with a two-state model of microtubule dynamic instability and favour an extended four-state model with two independent meta-stable pause states over a three-state model with a single pause state. Moreover, our data on kinetic state transitions rule out a simple GTP-cap model as the driving force of microtubule stabilization in egg extracts on time scales of a few seconds or longer. We determined the three-dimensional elastic properties of microtubules as a function of both the contour length and the dynamic state. Our results indicate that pausing microtubules are less flexible than growing microtubules and suggest a growth speed dependent persistence length. These data might hint towards mechanisms that enable microtubules to efficiently perform multiple different tasks in the cell and suggest the development of a unified model of microtubule dynamics and microtubule mechanics.
Key Words:
GTP-cap model, Xenopus laevis egg extracts, laser light-sheet based fluorescence microscopy, microtubule dynamic instability, microtubule elasticity, three-dimensional time-lapse imaging
