XMAP215 activity sets spindle length by controlling the total mass of spindle microtubules

Abstract

Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate their morphology and function. Today, we understand many details of microtubule assembly, the role of microtubule-associated proteins, and the action of molecular motors. Ultimately, the challenge remains to understand how the collective behaviour of these nanometre-scale processes gives rise to a properly sized spindle on the micrometre scale. By systematically engineering the enzymatic activity of XMAP215, a processive microtubule polymerase, we show that Xenopus laevis spindle length increases linearly with microtubule growth velocity, whereas other parameters of spindle organization, such as microtubule density, lifetime and spindle shape, remain constant. We further show that mass balance can be used to link the global property of spindle size to individual microtubule dynamic parameters. We propose that spindle length is set by a balance of non-uniform nucleation and global microtubule disassembly in a liquid-crystal-like arrangement of microtubules.

Spindle Size Scaling Contributes to Robust Silencing of Mitotic Spindle Assembly Checkpoint

“…Nonkinetochore microtubules (non-kMT) are the highly dynamical microtubules that seed throughout the spindle (41)(42)(43)(44). Non-kMTs likely assume largely an even density profile, similar to that observed in bipolar spindle self-assembled in Xenopus egg extract without centrosomes (17). While different interpretations are possible and not necessarily exclude each other, for brevity, we will call the two groups of microtubules kMT and non-kMT in the rest of the article.…”

“…Great efforts have been devoted to understanding the mechanics of spindle assembly pertaining to the first question-in particular, how different molecules modulate the size and shape of mitotic spindle (17)(18)(19)(20)(21)(22). It is not clear, however, whether the size scaling simply reflects the natural consequences of the mechanical process or additionally fulfills any functional roles in mitosis.…”

Cytoskeletal Symmetry Breaking and Chirality: From Reconstituted Systems to Animal Development

“…It should be pointed out that these gravity-dependent phenomena are restricted to non-physiologically dense in vitro preparations and their in vivo relevance is controversial [50][51][52], especially since forces generated in microtubule assemblies are orders of magnitude greater than those generated by gravity. However, independent of the forces needed to organize microtubules into liquid crystal-like states, there is recent bona fide evidence of liquid crystal-like behavior of microtubules in cells [53,54].…”

Error-prone meiotic division and subfertility in mice with oocyte-conditional knockdown of pericentrin

“…This altered spindle structure supports the idea that Pcnt plays a role in MT anchoring and focusing of meiotic spindle poles. Moreover, it points to potential differences in MT dynamics and the associated proteins that regulate MT length (Bowne-Anderson et al, 2015; Reber et al, 2013) between MTOCdependent and -independent spindle assembly. Live-cell imaging revealed significant delays in MT nucleation around the condensing chromosomes as well as disruption of spindle elongation and organization into a bi-polar structure that resulted in shorter broad spindles.…”