Robust gap repair in the contractile ring ensures timely completion of cytokinesis

Abstract

Using laser microsurgery, Silva et al. show that gaps in the contractile ring can be repaired at any stage of constriction, allowing for successful and timely cytokinesis. Their results support a contractile unit model for constriction of the cytokinetic ring.

Actin turnover maintains actin filament homeostasis during cytokinetic ring contraction

“…In addition, turnover of actin filaments has been proposed to generate contractile stress independently of myosin II ( Zumdieck et al, 2007 ; Mendes Pinto et al, 2012 ). Although experimental results that are consistent with a role for turnover in actomyosin ring contraction exist ( Pelham and Chang, 2002 ; Silva et al, 2016 ), experiments that test this hypothesis are scarce. Thus, the functional significance of turnover of actin and other ring proteins remains unknown.…”

Cytokinetic rings mind the gap

“…Most studies have focused on how this ring assembles at the right time and place, but how the ring behaves as it constricts remains largely unknown. reveal that the actomyosin ring can be rapidly repaired as it contracts, and their data favor the idea that the ring is composed of autonomous contractile units that make cytokinesis a highly robust process (2).…”

“…Ana Carvalho and colleagues at the i3S/IBMC/University of Porto decided to study constriction by using laser microsurgery to create gaps in the cytokinetic ring as it contracts. Led by postdoc Ana Silva, the researchers were able to sever GFP-myosin II–labeled rings formed in early C. elegans embryos, without damaging the neighboring plasma membrane (2). “We saw that the rings snapped open, but only to a limited extent; they didn’t fall apart,” Carvalho explains.…”

Molecular form and function of the cytokinetic ring

“…Myosin-II motors arranged at an angle to each other and bound to different actin filaments would slide the intact filaments past one another. The idea of myosin-II bouquets functioning as a motor unit is attractive because of the observed myosin-II clustering (Schroeder, 1990;Stachowiak et al, 2014;Takaine et al, 2015;Wollrab et al, 2016;McDonald et al, 2017) and the proposal that contractile units exist in the CRs of multiple organisms (Carvalho et al, 2009;Silva et al, 2016;Thiyagarajan et al, 2017). However, the finding that furrow ingression initiates while F-actin is still randomly oriented at the division plane (Spira et al, 2017) suggests that an alternative mode of contraction could be at work, at least early in cytokinesis.…”

“…Plasma membrane deposition and cortical architecture and dynamics must be coordinated with CR formation and contraction. Furthermore, although the CR generates force, other mechanisms of force generation likely exist given that yeast, amoebas and animal cells are able to divide in the absence of a robust CR under certain circumstances (Zang et al, 1997;Kanada et al, 2005;Carvalho et al, 2009;Ma et al, 2012;Mendes Pinto et al, 2012;Silva et al, 2016;Davies et al, 2018;Dix et al, 2018).…”