Distinct roles of nonmuscle myosin II isoforms for establishing tension and elasticity during cell morphodynamics

Abstract

Nonmuscle myosin II (NM II) is an integral part of essential cellular processes, including adhesion and migration. Mammalian cells express up to three isoforms termed NM IIA, B, and C. We used U2OS cells to create CRISPR/Cas9-based knockouts of all three isoforms and analyzed the phenotypes on homogeneous and micropatterned substrates. We find that NM IIA is essential to build up cellular tension during initial stages of force generation, while NM IIB is necessary to elastically stabilize NM IIA-generated tension. The knockout of NM IIC has no detectable effects. A scale-bridging mathematical model explains our observations by relating actin fiber stability to the molecular rates of the myosin crossbridge cycle. We also find that NM IIA initiates and guides co-assembly of NM IIB into heterotypic minifilaments. We finally use mathematical modeling to explain the different exchange dynamics of NM IIA and B in minifilaments, as measured in FRAP experiments.

Cell Shape and Forces in Elastic and Structured Environments: From Single Cells to Organoids

“…[120] As seen in Figure 3a, cell shapes in 3D collagen gels also show the invaginated arcs found for cells on adhesive micropatterns (compare Figures 1a and 2a), because the same competition between cortical surface tension and line tension in the contour is at play in 3D as in 2D. [94,121] Similar to 2D traction force microscopy, beads can be placed in the hydrogel to measure the displacement and use it to calculate the forces exerted by the cell, but the technical challenges are much larger in 3D than in 2D, due to the required 3D imaging and the complicated mechanical properties of the 3D gels, which necessarily have to be porous to allow for nutrient supply. [122] A different approach to using hydrogels to observe cellular force sensing is to spatiotemporally change the hydrogel stiffness with light and to observe cellular reactions to stiffness changes.…”

“…This can be explained with the introduction of an additional elastic line tension [93] or with a dynamical version of the interplay between tension and elasticity. [94] Recently, elliptical arcs have been described for the case when the stress fibers do not line the periphery, but pull toward the cell body. [95] Contour models can often be solved analytically and the dependance of input parameters on the solution as well as their biological meaning follow directly from the model.…”

Lack of skeletal muscle contraction disrupts fibrous tissue morphogenesis in the developing murine knee

“…For instance, when a sharp drop in tension occurs, cells activate a catabolic program resulting in matrix remodeling 38,39 and in certain cases can activate their non-muscle myosin mediated contractile machinery to correct the overall tension back to homeostatic levels. 40 Similarly, in cell constructs, changes in external tension are sensed, and coordinately contracted against, by the collective cell population. 41 Thus, loss of muscle contraction could cause a decrease in nascent tension that the patterned cells attempt to correct by collectively contracting-leading to the observed hyperelongated state (Figure 4).…”

Printed Electronic Devices and Systems for Interfacing with Single Cells up to Organoids

“…[175] More recently, this system has been applied to study the distinct roles of non-muscle myosin II isoforms for establishing cellular tension and during cellular homeostasis. [176] The vascularization of intricate cell cultures, such as organoids, has historically posed challenges. Nevertheless, Grebenyuk and co-workers have made notable progress in this area by introducing a synthetic 3D soft microfluidic system, fabricated through two-photon hydrogel polymerization.…”