Force‐ and kinesin‐8‐dependent effects in the spatial regulation of fission yeast microtubule dynamics

Abstract

Microtubules (MTs) are central to the organisation of the eukaryotic intracellular space and are involved in the control of cell morphology. For these purposes, MT polymerisation dynamics are tightly regulated. Using automated image analysis software, we investigate the spatial dependence of MT dynamics in interphase fission yeast cells with unprecedented statistical accuracy. We find that MT catastrophe frequencies (switches from polymerisation to depolymerisation) strongly depend on intracellular position. We provide evidence that compressive forces generated by MTs growing against the cell pole locally reduce MT growth velocities and enhance catastrophe frequencies. Furthermore, we find evidence for an MT length-dependent increase in the catastrophe frequency that is mediated by kinesin-8 proteins (Klp5/6). Given the intrinsic susceptibility of MT dynamics to compressive forces and the widespread importance of kinesin-8 proteins, we propose that similar spatial regulation of MT dynamics plays a role in other cell types as well. In addition, our systematic and quantitative data should provide valuable input for (mathematical) models of MT organisation in living cells.

Contributions of Microtubule Dynamic Instability and Rotational Diffusion to Kinetochore Capture

“…The torque can cause the MT tip to slip along the edge of the envelope, reorienting the MT, as has been measured and modeled previously for MTs interacting with microchamber boundaries (33)(34)(35). In addition, MTs that grow into a boundary exhibit increased catastrophe frequency (36). The force component along the MT long axis increases the catastrophe frequency, as measured previously (37,38).…”

Role and regulation of kinesin-8 motors through the cell cycle

“…One possibility is that the rate of Klp5-Klp6 movement on the lattice is set just below the maximum rate of microtubule tip growth so that Klp5-Klp6 motors only accumulate at the plus tips of paused microtubules. This is consistent with the observations that both the pausing of microtubule growth, microtubule catastrophe, and the accumulation of Klp5-Klp6 at the plus tips of interphase microtubules is more prevalent when microtubule tips near the cell end cortex, irrespective of microtubule length (Tischer et al 2009). Indeed it has been suggested that compressive forces, imposed by physical interaction of the growing microtubule tips with the cell end, may cause microtubules to pause by physically inhibiting new tubulin dimer incorporation into the microtubule tip (Tischer et al 2009).…”

“…This is consistent with the observations that both the pausing of microtubule growth, microtubule catastrophe, and the accumulation of Klp5-Klp6 at the plus tips of interphase microtubules is more prevalent when microtubule tips near the cell end cortex, irrespective of microtubule length (Tischer et al 2009). Indeed it has been suggested that compressive forces, imposed by physical interaction of the growing microtubule tips with the cell end, may cause microtubules to pause by physically inhibiting new tubulin dimer incorporation into the microtubule tip (Tischer et al 2009). Although such a model is difficult to disprove it does not explain why microtubules in cells lacking the Tea1 cell polarity factor fail to pause at cell ends (Mata and Nurse 1997).…”

A theory of microtubule catastrophes and their regulation

“…However, it has been proposed that motors from the depolymerizing kinesin-8 family induce catastrophes in a microtubule lengthdependent manner by walking processively to the plus end and removing the terminal tubulin subunit (18,19). These in vitro data are supported by live-cell imaging experiments in Schizosaccharomyces pombe that indicate that kinesin-8 motors induce catastrophe with a rate that depends on microtubule length (20).…”