Two-step interphase microtubule disassembly aids spindle morphogenesis

Nunu Mchedlishvili,Adam Corrigan,Helen K Matthews,Buzz Baum

doi:10.1186/s12915-017-0478-z

Nunu Mchedlishvili, Adam Corrigan + Show 2 more

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https://doi.org/10.1186/s12915-017-0478-z

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Abstract

BackgroundEntry into mitosis triggers profound changes in cell shape and cytoskeletal organisation. Here, by studying microtubule remodelling in human flat mitotic cells, we identify a two-step process of interphase microtubule disassembly.ResultsFirst, a microtubule-stabilising protein, Ensconsin/MAP7, is inactivated in prophase as a consequence of its phosphorylation downstream of Cdk1/cyclin B. This leads to a reduction in interphase microtubule stability that may help to fuel the growth of centrosomally nucleated microtubules. The peripheral interphase microtubules that remain are then rapidly lost as the concentration of tubulin heterodimers falls following dissolution of the nuclear compartment boundary. Finally, we show that a failure to destabilise microtubules in prophase leads to the formation of microtubule clumps, which interfere with spindle assembly.ConclusionsThis analysis highlights the importance of the step-wise remodelling of the microtubule cytoskeleton and the significance of permeabilisation of the nuclear envelope in coordinating the changes in cellular organisation and biochemistry that accompany mitotic entry.

Highlights

Entry into mitosis triggers profound changes in cell shape and cytoskeletal organisation
The interphase microtubule cytoskeleton is remodelled in two discrete steps at mitotic entry In order to explore the kinetics of microtubule remodelling upon entry into mitosis, we began by monitoring changes in the microtubule cytoskeleton organisation relative to loss of the nuclear-cytoplasmic compartment boundary (NEP) in HeLa cells stably expressing histone2B-monomeric red fluorescent protein and monomeric enhanced green fluorescent protein-α-tubulin [33]
In summary, our analysis reveals a two-step process by which interphase microtubules are disassembled upon entry into mitosis

Summary

Introduction

Entry into mitosis triggers profound changes in cell shape and cytoskeletal organisation. Microtubule cytoskeleton remodelling starts before NEP with a dramatic increase in microtubule nucleation at the centrosomes [1], driven by the recruitment and local activation of the gamma tubulin ring complex (γ − TuRC) [2,3,4,5]. Once cells are in prometaphase, highly dynamic microtubules emanating from the centrosomes search cell space for kinetochore attachment sites on which to capture chromosomes [7,8,9]. This stabilises the microtubules, leading to a rise in tubulin polymer levels during mitotic spindle formation [6, 10]. The final size of the spindle is determined by microtubule regulators [18] together with the total available pool of tubulin heterodimers [19]

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