Bridging Kinesin Properties with System-scale Characteristics of Microtubule-Motor Assemblies

Abstract

In a dividing cell, multiple subfamilies of kinesin and dynein motors work together to form the mitotic spindle out of microtubule filaments. This complex structure has incited much study into how it is formed and regulated. Knockdown experiments in cells yielded a number of insights, however, the complex environment of the cell prevents a detailed quantitative picture connecting biophysical motor properties to the resulting mesoscopic phenomena. However, in vitro, reconstituted systems of few purified components strip away the other reactions occuring within the cell, creating the opportunity to work from the bottom up. We use an optogenetic system wherein motor interactions are controlled by light to form microtubule structures such as asters. We connect length and speed scales of microtubule structures to motor properties such as speed and processivity by performing experiments with various kinesin motors. With this approach, we develop and test a model explaining how contraction speed varies with network size and motor speed. We also observe how the motors are distributed within microtubule structures and how that varies depending on the motor used. Further, we arrange competition between kinesins that walk towards opposite ends of the microtubules and demonstrate how this competition yields unique structures with properties that depend on both motors. This work is a step towards bridging microscopic motor properties to mesoscopic system-scale characteristics and answering the question of how cooperation between various kinesins can result in the generation of cellular structures.