An actin–myosin-II interaction is involved in maintaining the contractile ring in fission yeast

Abstract

The actomyosin-based contractile ring, which assembles at the cell equator, maintains its circularity during cytokinesis in many eukaryotic cells, ensuring its efficient constriction. Although consistent maintenance of the ring is one of the mechanisms underpinning cytokinesis, it has not yet been fully addressed. We here investigated the roles of fission yeast myosin-II proteins [Myo2 and Myo3 (also known as Myp2)] in ring maintenance during cytokinesis, with a focus on Myo3. A sitedirected mutational analysis showed that the motor properties of Myo3 were involved in its accumulation in the contractile ring. The assembled ring was often deformed and not properly maintained under conditions in which the activities of myosin-II proteins localizing to the contractile ring were decreased, leading to inefficient cell division. Moreover, Myo3 appeared to form motile clusters on the ring. We propose that large assemblies of myosin-II proteins consolidate the contractile ring by continuously binding to F-actin in the ring, thereby contributing to its maintenance.

Molecular form and function of the cytokinetic ring

“…In contrast, adding a motor-defective HMM mutant decreases the likelihood of ring formation, as does adding a passive crosslinker, such as α-actinin, although this can be rescued by the addition of HMM (Miyazaki et al, 2015). This finding is consistent with other observations showing that the levels of crosslinkers in the CR must be carefully balanced (Mukhina et al, 2007;Reichl et al, 2008;Mishra et al, 2013;Mavrakis et al, 2014;Takaine et al, 2015;Li et al, 2016;Descovich et al, 2018).…”

“…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.…”

Ginsenoside Rg1 Protects against Oxidative Stress-induced Neuronal Apoptosis through Myosin IIA-actin Related Cytoskeletal Reorganization

“…Myosin II is a molecular motor that binds and contracts filamentous actin (F-actin) by hydrolysis of ATP, converting chemical energy into mechanical forces 13. The forces also contribute to numerous cellular activities in a variety of cell types, including motility 14, 15, adhesion 16, neuritogenesis 17 and cytokinesis 18. In neuronal cells, myosin II induces synaptic dysfunction, growth cone collapse and the subsequent neurite retraction under various stimuli 19, 20.…”

Fission yeast myosin Myo2 is down-regulated in actin affinity by light chain phosphorylation

“…The binding partners of this region of Myo2 in the nodes are not established, but IQGAP Rng2 and anillin-like Mid1 have been implicated, based on localization dependency and immunoprecipitation experiments (4,11). Unlike the two other myosins in the contractile ring (Myp2, an uncharacterized class-II myosin, and Myo51, an unusual singleheaded class-V myosin) (12), Myo2 localization to the division site does not depend on actin filaments (11,13,14). Although Myo2's interactions with other node proteins are unresolved at the molec-ular level, a plausible model for Myo2 function is that it forms clusters by being stably anchored to nodes.…”