Two XMAP215/TOG Microtubule Polymerases, Alp14 and Dis1, Play Non-Exchangeable, Distinct Roles in Microtubule Organisation in Fission Yeast.

Masashi Yukawa,Tomoki Kawakami,Takashi Toda,Corinne Pinder

doi:10.3390/ijms20205108

Masashi Yukawa, Tomoki Kawakami + Show 2 more

Open Access

https://doi.org/10.3390/ijms20205108

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Abstract

Proper bipolar spindle assembly underlies accurate chromosome segregation. A cohort of microtubule-associated proteins orchestrates spindle microtubule formation in a spatiotemporally coordinated manner. Among them, the conserved XMAP215/TOG family of microtubule polymerase plays a central role in spindle assembly. In fission yeast, two XMAP215/TOG members, Alp14 and Dis1, share essential roles in cell viability; however how these two proteins functionally collaborate remains undetermined. Here we show the functional interplay and specification of Alp14 and Dis1. Creation of new mutant alleles of alp14, which display temperature sensitivity in the absence of Dis1, enabled us to conduct detailed analyses of a double mutant. We have found that simultaneous inactivation of Alp14 and Dis1 results in early mitotic arrest with very short, fragile spindles. Intriguingly, these cells often undergo spindle collapse, leading to a lethal “cut” phenotype. By implementing an artificial targeting system, we have shown that Alp14 and Dis1 are not functionally exchangeable and as such are not merely redundant paralogues. Interestingly, while Alp14 promotes microtubule nucleation, Dis1 does not. Our results uncover that the intrinsic specification, not the spatial regulation, between Alp14 and Dis1 underlies the collaborative actions of these two XMAP215/TOG members in mitotic progression, spindle integrity and genome stability.

Highlights

Microtubules (MTs) play diverse roles in a wide range of biological processes including cell cycle progression, development and differentiation pathways [1]
The seminal advancement of our understanding of the XMAP215/TOG family was the discovery that XMAP215 is a MT polymerase [11]; this protein is capable of incorporating α/β-tubulin heterodimers at the plus end of pre-existing MTs
To explore the physiological and phenotypic consequences resulting from simultaneous inactivation of two XMAP215/TOG paralogues in fission yeast, we sought to isolate temperaturesensitive mutants of alp14 in the dis1 deletion background

Summary

Introduction

Microtubules (MTs) play diverse roles in a wide range of biological processes including cell cycle progression, development and differentiation pathways [1]. The bipolar spindle functions as the division apparatus for sister chromatids, generating pulling forces to move them towards opposite poles to ensure equal partition of genetic material. Errors in this process can lead to cell death and/or aneuploidy, a major risk factor for miscarriage, birth defects and tumourigenesis [2,3]. This activity has been proven for other members of the family from a diverse range of organisms [8] Consistent with this notion, depletion or mutational inactivation of XMAP215/TOG family members generally results in the emergence of shorter, unstable MTs in various cell types [8]

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