Lateral Communication between Stress Fiber Sarcomeres Facilitates a Local Remodeling Response

Actin stress fibers (SFs) are load-bearing and mechanosensitive structures. To our knowledge, the mechanisms that enable SFs to sense and respond to strain have not been fully defined. Acute local strain events can involve a twofold extension of a single SF sarcomere, but how these dramatic local events affect the overall SF architecture is not believed to be understood. Here we have investigated how SF architecture adjusts to episodes of local strain that occur in the cell center. Using fluorescently tagged zyxin to track the borders of sarcomeres, we characterize the dynamics of resting sarcomeres and strain-site sarcomeres. We find that sarcomeres flanking a strain site undergo rapid shortening that directly compensates for the strain-site extension, illustrating lateral communication of mechanical information along the length of a stress fiber. When a strain-site sarcomere extends asymmetrically, its adjacent sarcomeres exhibit a parallel asymmetric shortening response, illustrating that flanking sarcomeres respond to strain magnitude. After extension, strain-site sarcomeres become locations of new sarcomere addition, highlighting mechanical strain as a trigger of sarcomere addition and revealing a, to our knowledge, novel type of SF remodeling. Our findings provide evidence to suggest SF sarcomeres act as strain sensors and are interconnected to support communication of mechanical information.