Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Abstract

Significance Animal cells continuously move, divide, and transmit forces by actively reorganizing their internal scaffold or cytoskeleton. Molecular motors pull actin filaments together and generate contraction of the cytoskeleton underneath the cell membrane. We address the detailed mechanism of contraction by using a minimal in vitro assay: a liposome membrane to which we attach actin filaments and molecular motors in a controlled manner. We reproduce contraction like in cells. We show that the scaffold needs to be tightly attached to the membrane for efficient contraction, but, under some conditions, efficient contraction can lead to liposome destruction. These results suggest that cells must precisely control their contractility to remain intact during cellular events.

Cytoskeletal Symmetry Breaking and Chirality: From Reconstituted Systems to Animal Development

“…The latter findings and the tunability of physical parameters of actin networks by small changes in cross-linker concentrations [87] might explain how contractile networks can undergo fast remodeling in vivo. This is also consistent with the interpretation from the Sykes laboratory that symmetry breaking in reconstituted systems can be attributed to rupture of spherical actin networks when cortical tension surpasses a certain threshold [100]. The threshold is determined by a concentration window of capping protein that limits growth of branched networks nucleated by the Arp2/3 complex, and by a sufficient number of motors that pull on actin filaments [101].…”

Apical constriction: themes and variations on a cellular mechanism driving morphogenesis

“…Despite having initially random F-actin orientations, reconstituted actin-myosin networks contract on length scales that are typical of a cell apex (∼10 μm) (Bendix et al, 2008;Soares e Silva et al, 2011;Murrell and Gardel, 2012;Carvalho et al, 2013). This suggests that an inherent actin filament polarity in the network is not a prerequisite for contraction.…”

Wrinkling of a spherical lipid interface induced by actomyosin cortex

“…tinct structures, such as network, cortex, and aster formations [15,[19][20][21][22]. However, the fundamental issues regarding the actomyosin cortex, i.e., how the mechanical contractile forces exerted by the actomyosin affect the deformable plasma membrane and its shape, remain poorly understood because of the difficulties of in vitro reconstruction, such as those posed by the establishment of effective coupling between actomyosin and membranes [20][21][22].…”

“…However, the fundamental issues regarding the actomyosin cortex, i.e., how the mechanical contractile forces exerted by the actomyosin affect the deformable plasma membrane and its shape, remain poorly understood because of the difficulties of in vitro reconstruction, such as those posed by the establishment of effective coupling between actomyosin and membranes [20][21][22]. Therefore, we sought to develop a model system that can exhibit the primitive aspects of cell membrane deformation due to the contractile force generated by membrane-coupled actomyosin.…”