Myosin-dependent actin stabilization as revealed by single-molecule imaging of actin turnover

Abstract

How mechanical stress applied to the actin network modifies actin turnover has attracted considerable attention. Actomyosin exerts the major force on the actin network, which has been implicated in actin stability regulation. However, direct monitoring of immediate changes in F-actin stability on alteration of actomyosin contraction has not been achieved. Here we reexamine myosin regulation of actin stability by using single-molecule speckle analysis of actin. To avoid possible errors attributable to actin-binding probes, we employed DyLight-labeled actin that distributes identical to F-actin in lamellipodia. We performed time-resolved analysis of the effect of blebbistatin on actin turnover. Blebbistatin enhanced actin disassembly in lamellipodia of fish keratocytes and lamellar of Xenopus XTC cells at an early stage of the inhibition, indicating that actomyosin contraction stabilizes cellular F-actin. In addition, our data show a previously unrecognized relationship between the actin network-driving force and the actin turnover rates in lamellipodia. These findings point to the power of direct viewing of molecular behavior in elucidating force regulation of actin filament turnover.

Regulation and dynamics of force transmission at individual cell-matrix adhesion bonds

“…4f). This velocity is approximately one-third the magnitude of Factin speeds measured in the lamellipodia of Xenopus XTC cells, a difference that may reflect a decrease in F-actin velocities near adhesions (31). Simulations produced a power-law distribution of F-actin velocities that was qualitatively similar to experimental observation, providing independent evidence that the model could capture the essential aspects of force transduction.…”

Regulation and dynamics of force transmission at individual cell-matrix adhesion bonds

“…The mean speed for F-actin within both adhesions and linear F-actin-rich structures (e.g., stress fibers) was 7.9 nm/s (95% confidence interval: 7.6-8.1 nm/s; 9 cells, 2355 tracks), comparable to the mean velocity of 5 nm/s observed in reversible crosslinker simulations. These measured and simulated velocities are approximately one-half to one-third the magnitude of F-actin speeds measured in the lamellipodia of Xenopus XTC cells, respectively, dif-ferences that may reflect a decrease in F-actin velocities near adhesions (36).…”

Talin-mediated force transmission and talin rod domain unfolding independently regulate adhesion signaling

“…In addition, many cellular processes are regulated by the level of mechanical tension transmitted through the actin cytoskeleton and adhesion complexes. Such processes include the assembly of fibronectin fibrils in the ECM, the severing of relaxed actin filaments by cofilins and the overall regulation of actin filament turnover (Hayakawa et al, 2011;Weinberg et al, 2017;Yamashiro et al, 2018). Through these force-dependent mechanisms, the mechanical linkage completed by a talin modulates the dynamics of adhesion proteins and regulates the stability and signaling of the adhesion complex.…”