The relationship between time until catastrophe and growth velocity is the same in the presence (circles) or absence (triangles) of force.
In the article, Janson et al. use an in vitro assay to show that force on microtubules leads to microtubule shortening. The group measured the time required for microtubules to reach catastrophe, the point at which growing polymers start to shorten. Microtubules that contacted a synthetic barrier experienced forces that hastened catastrophe. Stronger forces had increasingly larger effects on growth velocity, by lowering the rate of tubulin addition. The relationship between growth velocity and the time until catastrophe was the same in the presence or absence of force. Thus, force's only contribution to shortening is to decrease growth velocity. A delay before addition of the next tubulin dimer could...
