Microtubule plus-ends act as physical signaling hubs to activate RhoA during cytokinesis.

Vikash Verma,Thomas J Maresca

doi:10.7554/elife.38968

Abstract

Microtubules (MTs) are essential for cleavage furrow positioning during cytokinesis, but the mechanisms by which MT-derived signals spatially define regions of cortical contractility are unresolved. In this study cytokinesis regulators visualized in Drosophila melanogaster (Dm) cells were found to localize to and track MT plus-ends during cytokinesis. The RhoA GEF Pebble (Dm ECT2) did not evidently tip-track, but rather localized rapidly to cortical sites contacted by MT plus-tips, resulting in RhoA activation and enrichment of myosin-regulatory light chain. The MT plus-end localization of centralspindlin was compromised following EB1 depletion, which resulted in a higher incidence of cytokinesis failure. Centralspindlin plus-tip localization depended on the C-terminus and a putative EB1-interaction motif (hxxPTxh) in RacGAP50C. We propose that MT plus-end-associated centralspindlin recruits a cortical pool of Dm ECT2 upon physical contact to activate RhoA and to trigger localized contractility.

Highlights

Cell division ends with the formation of an actomyosin contractile ring, positioned midway between the segregated chromosomes
It has long been known that the centralspindlin complex and chromosomal passenger complex (CPC) are highly enriched in the midzone during cytokinesis (Glotzer, 2009); previous studies in Drosophila and mammalian cells as well as Xenopus embryos have reported MT plus-tip localization of the centralspindlin complex as well as the CPC component Aurora B kinase (ABK) (Breznau et al, 2017; Nishimura and Yonemura, 2006; Vale et al, 2009)
We had previously shown that contractile myosin rings assembled normally on concanavalin A (Con A) (Ye et al, 2016), but since such a treatment could interfere with furrow formation, the effects of Con A on cytokinesis was further assessed by overnight time-lapse imaging of Schneider 2 (S2) cells seeded on Con A

Summary

Introduction

Cell division ends with the formation of an actomyosin contractile ring, positioned midway between the segregated chromosomes. The spindle apparatus specifies the position of the cleavage furrow during anaphase (Rappaport, 1961), and it is widely accepted that the cleavage plane is positioned via microtubule (MT)-dependent mechanisms (Rappaport, 1996); there is lack of consensus regarding the nature and molecular composition of the MT-derived positioning signals and how they are delivered While it has been posited in different models that distinct MT populations spatially regulate stimulation or relaxation of cortical contractility, decades of work on the topic have revealed the existence of redundant pathways that contribute to furrow positioning to various degrees in different organisms and developmental stages. Present understanding of how the population of MTs examined in this study (astral MTs) contributes to the robustness of cleavage furrow positioning in unperturbed mitoses is limited

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Conclusion