Theory of cytoskeletal rearrangement and force generation*

Cytoskeletal networks that include microtubules, crosslinkers, and kinesin motors are the basis of the mitotic spindle and cytoplasmic transport. The large separation of time scales between motor and crosslinker activity (sub-second to second) and network function (minutes to hours) is a challenge for theoretical approaches. We developed a minimal model, building on the separation of time scales between relatively fast crosslinker and motor rearrangement and relatively slow filament movement. The model reproduces experimentally measured force, torque, and self-organization in cytoskeletal networks of different length scales. With this model, we study mitotic spindle assembly from a monopolar initial condition and compare the mechanisms of motor- versus crosslinker-mediated spindle assembly. The results show how torque-balance and force-balance properly align microtubule bundles. In another study, we propose that oscillating optically trapped microtubule pairs crosslinked with motors and/or crosslinkers can be used to determine the kinetics and mechanics of crosslinking proteins.