Editorial: Membrane and Cytoskeleton Mechanics

As two main structural components of a cell, the lipid bilayer membrane [1] and cytoskeleton [2] are responsible for stabilizing the cell shape as well as playing key roles in different cellular functions. For example, important processes like cell migration [3–6], division [7, 8], and embryo development [9, 10] are all driven by internal forces generated within the cytoskeleton. In addition, various mechanosensitive proteins in the membrane allow cells to probe their microenvironment and perform functions such as mechano-transduction [11, 12] and volume regulation [13, 14]. For these reasons, extensive efforts have been devoted in the past few decades to elucidating key factors dictating the mechanical response of the lipid membrane and cytoskeleton [15–18] as well as connecting them to the capability of cells to perform biological duties or the progression of diseases such as cancer [19] and malaria [20]. This research topic intends to present a collection of substantial advances made in this field recently. The paper by Burgos-Bravo et al. shows that proteoglycan receptor Syndecan-4 can form a ternary complex with αVβ3 integrin and the neuronal protein Thy-1, increase the lifetime of Thy-1 – αVβ3 integrin binding, modulate their mechano-transduction function, and eventually result in faster neurite retraction and suppressed neurite outgrowth under pro-inflammatory conditions. The paper by Ricketts et al. focuses on how ionic conditions influence the rearrangement of networks of actin and microtubules. Specifically, the authors show that the bulk contraction of both actin and actin-microtubule networks increases when Mg concentrations varies from 2 to 20 mM. Interestingly, actin networks begin to contract at lower Mg concentrations and shorter times than actin-microtubule networks. These results shed light on how varying environmental conditions can dynamically tune the morphology of the cytoskeleton without the help of motor proteins. The paper by Bashirzadeh et al. discusses how the properties of actin crosslinkers and surrounding confinement geometry regulate the formation of actin bundles and bundle networks. Specifically, depending on the size of giant unilamellar vesicles (GUVs) encapsulating actin and concentration of fascin, a short crosslinker, straight F-actin bundles, or crosslinked bundle networks can be formed. In addition, the authors also show that the presence of a long crosslinker, α-actinin, impacts fascininduced GUV shape changes and significantly impairs the formation of filopodia-like protrusions. The paper by Dasanna et al. presents how the contrast/ratio of viscosities between RBC cytosol and blood plasma affects the shape and dynamics of RBCs via mesoscopic hydrodynamics simulations. Interestingly, it is found that distinct RBC shapes, including tumbling cells, parachutes, and tank-treading slippers, can all appear depending on the values of viscosity contrast, flow rate, and tube diameter. Furthermore, the authors demonstrate that the tumbling-to-slipper transition, as well as the size of the parachute region, is strongly affected by viscosity contrast. The paper by Galluzzi et al. discusses the influence of photothermal effects of fluorescent dyes on the mechanical response and stability of membranes. Specifically, the authors show a 30 min laser Edited and reviewed by: Ralf Metzler, University of Potsdam, Germany