Forces inside cells play a fundamental role in cell behavior, for example in cancer cell migration. We focus on the vinculin protein which is involved in the stabilization of cell adhesion.
Through fluorescence transfer (FRET), forces within vinculin can be measured with picoNewton sensitivity. We measure these internal forces while applying a calibrated external force with a laser-based optical tweezer via a microbead attached to the cell.
Our most recent results using fibroblast cells show that the force applied with the optical tweezer induces the recruitment of vinculin and the formation of focal adhesions on the bead within a few minutes. Once the bead is attached to the cell, we record its trajectory and infer the force exerted by the cell. We correlate this force with the FRET efficiency of the force sensor.
SignificanceForces inside cells play a fundamental role in tissue growth, affecting important processes such as cancer cell migration or tissue repair after injury. Förster resonance energy transfer (FRET)-based tension sensors are a remarkable tool for studying these forces and should be made easier to use.AimWe prove that absolute FRET efficiency can be measured on a simple setup, an order of magnitude more cost-effective than a standard FRET microscopy setup, by applying it to vinculin tension sensors (VinTS) at the focal adhesions of live CHO-K1 cells.ApproachOur setup located at Université Paris-Saclay acquires donor and acceptor fluorescence in parallel on two low-cost CMOS cameras and uses two LEDs for rapid switching of the excitation wavelength at a reduced cost. The calibration required to extract FRET efficiency was achieved using a single construct (TSMod). FRET efficiencies were measured for VinTS and the tail-less control VinTL, lacking the actin-binding domain of vinculin. Measurements were confirmed on the same cell type using a more standard intensity-based setup located at Rutgers University.ResultsThe average FRET efficiency of VinTS (22.0 % ± 4 % ) over more than 10,000 focal adhesions is significantly lower (p < 10 − 6) than that of VinTL (30.4 % ± 5 % ), our control that is insensitive to force, in agreement with the force exerted on vinculin at focal adhesions. Attachment of the CHO-K1 cells on fibronectin decreases FRET efficiency, thus increasing the force, compared with poly-lysine. FRET efficiency for the VinTL control is consistent with all measurements currently available in the literature, confirming the validity of our measurements and hence of our simpler setup.ConclusionsForce measurements, resolved spatially inside a cell, can be achieved using FRET-based tension sensors with a cost effective intensity-based setup. This will facilitate combining FRET with techniques for applying controlled forces such as optical tweezers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.