Motor function in interpolar microtubules during metaphase

TL;DR

This study models microtubule fluctuations driven by opposing kinesin motors as a one-dimensional random walk, aligning theoretical predictions with experimental data and exploring motor concentration effects on spindle length control.

Contribution

It introduces a stochastic model of microtubule dynamics influenced by antagonistic motors, linking experimental observations to a random walk framework and analyzing motor concentration impacts.

Findings

Fluctuation amplitudes match experimental observations.

Antagonistic motors can restrict microtubule movement but not perfectly.

Varying motor concentrations enhances spindle length control.

Abstract

We analyze experimental observations of microtubules undergoing small fluctuations about a "balance point" when mixed in solution of two different kinesin motor proteins, KLP61F and Ncd. It has been proposed that the microtubule movement is due to stochastic variations in the densities of the two species of motor proteins. We test this hypothesis here by showing how it maps onto a one-dimensional random walk in a random environment. Our estimate of the amplitude of the fluctuations agrees with experimental observations. We point out that there is an initial transient in the position of the microtubule where it will typically move of order its own length. We compare the physics of this gliding assay to a recent theory of the role of antagonistic motors on restricting interpolar microtubule sliding of a cell's mitotic spindle during prometaphase. It is concluded that randomly positioned antagonistic motors can restrict relative movement of microtubules, however they do so imperfectly. A variation in motor concentrations is also analyzed and shown to lead to greater control of spindle length.