Repetitive stretching of giant liposomes utilizing the nematic alignment of confined actin

Shunsuke Tanaka,Masahito Hayashi,Kingo Takiguchi

doi:10.1038/s42005-018-0019-2

Shunsuke Tanaka, Masahito Hayashi + Show 1 more

Open Access

https://doi.org/10.1038/s42005-018-0019-2

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Abstract

Giant liposomes encapsulating cytoskeletons have been constructed to further understand the mechanisms of cell movement and develop cell-sized chemical machineries. Innovative studies demonstrating liposomal movements using microtubules and the molecular motors kinesin/dynein have been reported. However, no one has succeeded in generating repetitive motions controlled by external stimuli. Here we show that if the actin concentration in liposomes is comparable to that of cytoplasm of living cells, the liposomes can be deformed into spindle shapes by encapsulating only actin filaments, even without the molecular motor myosin. Furthermore, their shapes can be changed reversibly between spindle and sphere shapes by adjusting osmotic pressure or by light irradiation of fluorescent-labeled actin. In the latter case, the repetitive shape changes are accompanied with stretching and shrinking of filopodia- or acrosome projection-like extensions. Our results indicate that filamentous polymer of variable length like actin filament is a potential material for the reproduction of cell-like movement.

Highlights

Giant liposomes encapsulating cytoskeletons have been constructed to further understand the mechanisms of cell movement and develop cell-sized chemical machineries
We demonstrate that liposomes encapsulating F-actin at high concentrations comparable to the cytoplasm of living cells deform to a spindle shape, which is attributable to the nematic liquid crystal formation of F-actin
This study demonstrated that if actin filaments are contained in cell-sized giant liposomes at high concentrations comparable to the cytoplasmic level, the liposomes spontaneously deform to spindle-like shapes even without any actin-binding proteins such as gelation or bundling factors or molecular motor myosins

Summary

Introduction

Giant liposomes encapsulating cytoskeletons have been constructed to further understand the mechanisms of cell movement and develop cell-sized chemical machineries. We show that if the actin concentration in liposomes is comparable to that of cytoplasm of living cells, the liposomes can be deformed into spindle shapes by encapsulating only actin filaments, even without the molecular motor myosin Their shapes can be changed reversibly between spindle and sphere shapes by adjusting osmotic pressure or by light irradiation of fluorescent-labeled actin. Brief irradiation with strong excitation light can sever F-actin containing fluorescent-labeled monomers but they can subsequently repolymerize or anneal spontaneously, resulting in filament length switching and a reversible deformation between spindle-shaped liposomes and sphere-shaped liposomes possessing filopodia- or acrosome projection-like extensions. Those extensions can pull the liposome body during contraction

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