Three-dimensional microtubule behavior in Xenopus egg extracts reveals four dynamic states and state-dependent elastic properties.
Although microtubules are key players in many cellular processes, 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, growth and shrinkage. However, several studies have indicated that such a model does not provide a comprehensive quantitative and qualitative description of microtubule behavior. Using three-dimensional laser light-sheet fluorescence microscopy and a three-dimensional sample preparation in spacious Teflon cylinders, 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 favor an extended four-state model with two independent metastable 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 timescales 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 toward 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.
Keller
Philipp J
PJ
Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany. keller@embl.de
Pampaloni
Francesco
F
Lattanzi
Gianluca
G
Stelzer
Ernst H K
EH
D000818:Animals; D004548:Elasticity; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008870:Microtubules / Q000737:chemistry* / Q000648:ultrastructure*; D010063:Ovum / Q000737:chemistry*; D013314:Stress, Mechanical; D014982:Xenopus laevis