Geometry and network connectivity govern the mechanics of stress fibers

Abstract

Actomyosin stress fibers (SFs) play key roles in driving polarized motility and generating traction forces, yet little is known about how tension borne by an individual SF is governed by SF geometry and its connectivity to other cytoskeletal elements. We now address this question by combining single-cell micropatterning with subcellular laser ablation to probe the mechanics of single, geometrically defined SFs. The retraction length of geometrically isolated SFs after cutting depends strongly on SF length, demonstrating that longer SFs dissipate more energy upon incision. Furthermore, when cell geometry and adhesive spacing are fixed, cell-to-cell heterogeneities in SF dissipated elastic energy can be predicted from varying degrees of physical integration with the surrounding network. We apply genetic, pharmacological, and computational approaches to demonstrate a causal and quantitative relationship between SF connectivity and mechanics for patterned cells and show that similar relationships hold for nonpatterned cells allowed to form cell-cell contacts in monolayer culture. Remarkably, dissipation of a single SF within a monolayer induces cytoskeletal rearrangements in cells long distances away. Finally, stimulation of cell migration leads to characteristic changes in network connectivity that promote SF bundling at the cell rear. Our findings demonstrate that SFs influence and are influenced by the networks in which they reside. Such higher order network interactions contribute in unexpected ways to cell mechanics and motility.cytoskeleton | active cable model | actin | myosin | cell migration

Stress fibers are embedded in a contractile cortical network

“…Previous work has suggested that discrete connections of a peripheral stress fiber to other internal fibers can affect its relaxation pattern after severing (Kassianidou et al, 2017(Kassianidou et al, , 2019. However, the incomplete relaxation pattern of the severed peripheral stress fibers we observed here was not systematically associated with interconnections with internal fibers, as illustrated by the absence of visible fibers connected to the peripheral stress fibers in Figure 2a.…”

“…Hence, directional forces along specific actomyosin bundles can propagate to other bundles with which they are inter-connected. As a consequence, the tension in a stress fiber does not only depend on forces produced in that fiber but also on the connection and orientation of adjacent fibers (Kassianidou et al, 2017). This high degree of connection between actomyosin bundles can provide the mechanical coherence at the level of the cell (Chapin et al, 2012;Rossier et al, 2010;Smith et al, 2010).…”

Cytoskeletal Anisotropy Controls Geometry and Forces of Adherent Cells

“…n · T = 0). As shown by Kassianidou et al [35], isolated stress fibers can also exert localized contractile forces on the cell contour, leading to kinks and piecewise constant curvature. Consistent with our experiments, here we consider the case in which the density of the stress fibers is sufficiently high and uniform to approximate their mechanical effect in terms of a continuous anisotropic stress.…”

Traction forces control cell-edge dynamics and mediate distance-sensitivity during cell polarization

“…They are believed to drive cell motion, shape changes, and extracellular matrix remodeling [1][2][3]. However, most of the traction force analysis has been performed on stationary cells, investigating forces at the level of individual focal adhesions or linking them to static cell parameters such as area and edge curvature [4][5][6][7][8][9][10]. It is not well understood how traction forces are related to shape changes and motion, e.g.…”