Microtubule Organization in Three-Dimensional Confined Geometries:Evaluating the Role of Elasticity Through a Combined In Vitro and Modeling Approach

¹ UMR168 - Institut Curie
² Physics Department, Utrecht University
³ Wageningen University, Laboratory of Plant Cell Biology
⁴ FOM Institute AMOLF

^* To whom correspondence should be addressed. E-mail: mcl{at}curie.fr.

Submitted on November 7, 2005
Revised on December 19, 2005
Accepted on 16 October 2006

	Abstract

Microtubules or microtubule bundles in cells often grow longer than the size of the cell, which causes their shape and organization to adapt to constraints imposed by the cell geometry. We test the reciprocal role of elasticity and confinement in the organization of growing microtubules in a confining box-like geometry, in the absence of other (active) microtubule-organizing processes. This is inspired, for example, by the cortical microtubule array of elongating plant cells, where microtubules are typically organized in an aligned array transverse to the cell elongation axis. The method we adopt is a combination of analytical calculations, in which the polymers are modeled as inextensible filaments with bending elasticity confined to a two dimensional surface that defines the limits of a three-dimensional space, and in vitro experiments, in which microtubules are polymerized from nucleation seeds in micro-fabricated chambers. We show that these features are sufficient to organize the polymers in aligned, coiling configurations as for example observed in plant cells. Though elasticity can account for the regularity of these arrays, it cannot account for a transverse orientation of microtubules to the cell’s long axis. We therefore conclude that an additional active, forcegenerating process is necessary to create a coiling configuration perpendicular to the long axis of the cell.

Key Words: cytoskeleton, in vitro, microtubules, modeling, organization, plant cell