Abstract
Constriction of the cytokinetic ring, a circular structure of actin filaments, is an essential step during cell division. Mechanical forces driving the constriction are attributed to myosin motor proteins, which slide actin filaments along each other. However, in multiple organisms, ring constriction has been reported to be myosin independent. How actin rings constrict in the absence of motor activity remains unclear. Here, we demonstrate that anillin, a nonmotor actin crosslinker, indispensable during cytokinesis, autonomously propels the contractility of actin bundles. Anillin generates contractile forces of tens of pico-Newtons to maximise the lengths of overlaps between bundled actin filaments. The contractility is enhanced by actin disassembly. When multiple actin filaments are arranged into a ring, this contractility leads to ring constriction. Our results indicate that passive actin crosslinkers can substitute for the activity of molecular motors to generate contractile forces in a variety of actin networks, including the cytokinetic ring.
Highlights
Constriction of the cytokinetic ring, a circular structure of actin filaments, is an essential step during cell division
We show in a minimal reconstituted system that constriction of actin rings can be solely propelled by anillin, a nonmotor actin crosslinking and scaffolding protein highly enriched in the contractile ring during cytokinesis[22,23,24]
We found mobile filaments moving diffusively along the immobilised filaments (Fig. 1g, h, Movie 1), showing that anillinGFP generates a diffusible link between actin filaments
Summary
Constriction of the cytokinetic ring, a circular structure of actin filaments, is an essential step during cell division. Mechanical forces driving the constriction are attributed to myosin motor proteins, which slide actin filaments along each other. Theoretical and experimental works suggest that possible sources of the driving force underlying myosin-independent constriction mechanisms could depend on actin-crosslinking proteins and actin filament disassembly[15,16,17,18,19,20,21]. We show in a minimal reconstituted system that constriction of actin rings can be solely propelled by anillin, a nonmotor actin crosslinking and scaffolding protein highly enriched in the contractile ring during cytokinesis[22,23,24]. We demonstrate that diffusible filament crosslinkers, such as anillin, can generate contractile forces in actin networks, substituting for molecular motor activity
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