Turn-key super-resolution mapping of cell receptor force orientation and magnitude using a commercial structured illumination microscope

Abstract Many cellular processes, including cell division, development, and cell migration require spatially and temporally coordinated forces transduced by cell surface receptors. Nucleic acid-based molecular tension probes allow one to quantify and visualize the piconewton (pN) forces applied by these receptors. Building on this technology, we recently imaged DNA tension probes using fluorescence polarization imaging to map the magnitude and 3D orientation of receptor forces with diffraction limited resolution (~ 250 nm). Further improvements in spatial resolution are desirable as many force-sensing receptors are organized at the nano-scale in supramolecular complexes such as focal adhesions. Here, we show that structured illumination microscopy (SIM), a super-resolution technique, can be used to perform super-resolution molecular force microscopy (MFM). Using SIM-MFM, we generate the highest resolution maps of both the magnitude and orientation of the pN traction forces applied by cells. We apply SIM-MFM to map platelet and fibroblast integrins forces, as well as T cell receptor forces. The method reveals that platelets dynamically re-arrange the orientation of their integrin forces during activation. Monte Carlo simulations validated the results and provided analysis of the sources of noise. Importantly, we envision that SIM-MFM will be broadly adopted by the cell biology and mechanobiology communities because it can be implemented on any standard SIM microscope without hardware modifications.