Microtubule motor protein dynein mediates the collapse of the mitotic spindle following ablation in fission yeast S. pombe

A large molecular machine called the mitotic spindle segregates chromosomes during eukaryotic cell division. The spindle of the fission yeast Schizosaccharomyces pombe consists of a bundle of microtubules (protein filaments) within an intact nuclear envelope. During spindle elongation, motor proteins slide antiparallel microtubules apart while resisting the nucleus's compressive forces. We probe this force balance by severing the spindle via laser ablation. Similar to previous studies [1,2], we find that after cutting the spindle in half, the fragments rapidly collapse towards each other, often reattach, and resume elongation. While this behavior has been previously observed, many questions remain about its dynamics, mechanics, and molecular requirements. In this work, we find that previously hypothesized viscoelastic relaxation of the nucleus cannot fully explain spindle shortening in response to laser ablation. Instead, spindle collapse requires microtubule dynamics and is powered at least partly by the motor protein dynein. These results suggest a role for dynein in redundantly supporting force balance and bipolarity in the S. pombe spindle.
[1] Khodjakov et al. Curr Biol 2004. [2] Tolic-Nørrelykke et al Curr Biol 2004.