Tension-dependent Myosin Dynamics on Contractile Actomyosin Structures

The actomyosin cytoskeleton powers dynamic cellular processes by generating mechanical tension. Myosin dynamics must be regulated to maintain proper mechanical tension. Tension itself has been proposed to regulate myosin dynamics. Although in vitro studies have shown that myosin detaches slower from F-actin under resisting load, it is unclear whether mechanical tension can regulate myosin dynamics in cells. In this work, we assess myosin turnover dynamics on stress fibers with fluorescence recovery after photobleaching (FRAP) experiments. We reduce global cellular tension with pharmacological inhibitors at non-saturating doses, which decreases the total traction force while preserving the overall actomyosin architecture. Myosin recovers much faster after photobleaching under reduced tension, suggesting that myosin dissociates faster. The smaller immobile fraction suggests that non-exchanging myosin molecules become dynamic when tension is reduced. Indeed, quasi-sarcomeric myosin bands along individual stress fibers are more disordered and dynamic under reduced tension. Furthermore, we directly modulate tension on stress fibers by inducing strain sites. Myosin FRAP recovery adjacent to the strain site would shed light on the role of mechanical tension regulating myosin dynamics.