Mitotic Acetylation of Microtubules Promotes Centrosomal PLK1 Recruitment and Is Required to Maintain Bipolar Spindle Homeostasis

Sylvia Fenosoa Rasamizafy,Nathalie Morin,Juliette van Dijk,Gabriel Rabeharivelo,Julien Cau,Claude Delsert

doi:10.3390/cells10081859

Abstract

Tubulin post-translational modifications regulate microtubule properties and functions. Mitotic spindle microtubules are highly modified. While tubulin detyrosination promotes proper mitotic progression by recruiting specific microtubule-associated proteins motors, tubulin acetylation that occurs on specific microtubule subsets during mitosis is less well understood. Here, we show that siRNA-mediated depletion of the tubulin acetyltransferase ATAT1 in epithelial cells leads to a prolonged prometaphase arrest and the formation of monopolar spindles. This results from collapse of bipolar spindles, as previously described in cells deficient for the mitotic kinase PLK1. ATAT1-depleted mitotic cells have defective recruitment of PLK1 to centrosomes, defects in centrosome maturation and thus microtubule nucleation, as well as labile microtubule-kinetochore attachments. Spindle bipolarity could be restored, in the absence of ATAT1, by stabilizing microtubule plus-ends or by increasing PLK1 activity at centrosomes, demonstrating that the phenotype is not just a consequence of lack of K-fiber stability. We propose that microtubule acetylation of K-fibers is required for a recently evidenced cross talk between centrosomes and kinetochores.

Highlights

Microtubules (MTs) are long hollow tubes made of 13 protofilaments, formed by the polymerization of αβ-tubulin heterodimers [1]
To better observe centrosomes of ATAT1-depleted MT spindles, we co-stained siATAT1 cells for the centrosomal component γ-tubulin and the microtubule-associated protein TPX2 which is crucial for spindle formation. γ-Tubulin staining of ATAT1-depleted spindles can be resolved as two dots that are either in different planes or in the same plane while TPX2 decorates MTs in close proximity to the centrosomes (Figure 1b)
We decided to analyze whether MT acetylation of subsets of spindle MTs contributes to mitotic spindle plasticity

Summary

Introduction

Microtubules (MTs) are long hollow tubes made of 13 protofilaments, formed by the polymerization of αβ-tubulin heterodimers [1]. Elongation and shrinkage of MTs results from polymerization/depolymerization of tubulin subunits. Controlled and differential regulation of MT dynamics results in the arrangement of strikingly different MT networks, allowing specific cell functions. Examples are the long bundled MTs which regulate the elongation of axons in neurons, while, in mitosis, chromatid alignment and their subsequent faithful separation depends upon the organization of MTs into a mitotic spindle. MT behavior and specialization requires binding of microtubule-associated-proteins (MAPs) and molecular motors. It is generally accepted that specific tubulin isotypes and post-translational modifications (PTMs) mark MTs for spatial and temporal recruitment of specific MAPs and motors, exemplifying the “tubulin code” [2]

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