Abstract
Cytokinesis in eukaryotic cells is often accompanied by actomyosin cortical flow. Over 30 years ago, Borisy and White proposed that cortical flow converging upon the cell equator compresses the actomyosin network to mechanically align actin filaments. However, actin filaments also align via search-and-capture, and to what extent compression by flow or active alignment drive furrow formation remains unclear. Here, we quantify the dynamical organization of actin filaments at the onset of ring assembly in the C. elegans zygote, and provide a framework for determining emergent actomyosin material parameters by the use of active nematic gel theory. We characterize flow-alignment coupling, and verify at a quantitative level that compression by flow drives ring formation. Finally, we find that active alignment enhances but is not required for ring formation. Our work characterizes the physical mechanisms of actomyosin ring formation and highlights the role of flow as a central organizer of actomyosin network architecture.
Highlights
Cytokinesis begins in late anaphase, triggered by regulatory pathways with feedback from the mitotic spindle that ensure appropriate positioning of the molecular machinery
We set out to address this question in the one cell embryo of the nematode C. elegans which forms two constricting ingressions, first a pseudocleavage furrow during polarity establishment, and a cytokinetic furrow during cytokinesis (Figure 1—figure supplement 1a, Video 1) (Munro and Bowerman, 2009; Rose et al, 1995)
Cell Biology Biophysics and Structural Biology eLife digest Just under the surface of every animal cell, a thin and dynamic network of filaments called the cell cortex acts as a scaffold and determines the cell’s shape
Summary
Cytokinesis begins in late anaphase, triggered by regulatory pathways with feedback from the mitotic spindle that ensure appropriate positioning of the molecular machinery (reviewed in Fededa and Gerlich, 2012; Green et al, 2012). The small regulatory GTPase RhoA (Piekny et al, 2005; Tse et al, 2012) and the molecular motor myosin (Shelton et al, 1999; Werner and Glotzer, 2008) are enriched in an equatorial band (Piekny et al, 2005; Werner and Glotzer, 2008). Myosin can directly organize the actin network (Miller et al, 2012; Soares e Silva et al, 2011; Vavylonis et al, 2008), and if myosin-based active alignment (e.g. via search-and-capture [Vavylonis et al, 2008]) or flow-based compression as proposed by White and Borisy (White and Borisy, 1983; Rappaport, 1996) drive furrow formation and cytokinesis in eukaryotes remains unclear (Green et al, 2012; Bray and White, 1988; Levayer and Lecuit, 2012; Mendes Pinto et al, 2013; Cao and Wang, 1990; Murthy and Wadsworth, 2005; Zhou and Wang, 2008)
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