DNA-Based Optical Sensors for Forces in Cytoskeletal Networks

Mechanical forces are relevant for many biological processes, from wound healing and tumor formation to cell migration and differentiation. Cytoskeletal actin is largely responsible for responding to forces and transmitting them in cells, while also maintaining cell shape and integrity. Here, we describe a FRET-based hybrid DNA-protein tension sensor that is designed to sample transient forces in actin networks by employing two actin-binding motifs with a fast off-rate attached to a central DNA hairpin loop. Such a sensor will be useful to monitor rapidly changing stresses in the cell cytoskeleton. We use fluorescence lifetime imaging to determine the FRET efficiency and thereby the conformational state of the sensor, which makes the measurement robust against intensity variations. We demonstrate the applicability of the sensor by confocal microscopy and by monitoring crosslinking activity in in vitro actin networks by bulk rheology.