Linear Correlation between Active and Resistive Stresses Provides Information on Force Generation and Stress Transmission in Adherent Cells

Dynamics of centipede locomotion revealed by large-scale traction force microscopy

We present a novel approach to traction force microscopy (TFM) for studying the locomotion of 10 cm long walking centipedes on soft substrates. Leveraging the remarkable elasticity and ductility of kudzu starch gels, we use them as a deformable gel substrate, providing resilience against the centipedes' sharp leg tips. By optimizing fiducial marker size and density and fine-tuning imaging conditions, we enhance measurement accuracy. Our TFM investigation reveals traction forces along the centipede's longitudinal axis that effectively counterbalance inertial forces within the 0-10 mN range, providing the first report of non-vanishing inertia forces in TFM studies. Interestingly, we observe waves of forces propagating from the head to the tail of the centipede, corresponding to its locomotion speed. Furthermore, we discover a characteristic cycle of leg clusters engaging with the substrate: forward force (friction) upon leg tip contact, backward force (traction) as the leg pulls the substrate while stationary, and subsequent forward force as the leg tip detaches to reposition itself in the anterior direction. This work opens perspectives for TFM applications in ethology, tribology and robotics.

Impact of baculoviral transduction of fluorescent actin on cellular forces

Live staining of actin brings valuable information in the field of mechanobiology. Gene transfer of GFP-actin has been reported to disturb cell rheological properties while gene transfer of fluorescent actin binding proteins was not. However the influence of gene transfer on cellular forces in adhered cells has never been investigated. This would provide a more complete picture of mechanical disorders induced by actin live staining for mechanobiology studies. Indeed, most of these techniques were shown to alter cell morphology. Change in cell morphology may in itself be sufficient to perturb cellular forces. Here we focus on quantifying the alterations of cellular stresses that result from baculoviral transduction of GFP-actin in MDCK cell line. We report that GFP-actin transduction increases the proportion of cells with large intracellular or surface stresses, especially in epithelia with low cell density. We show that the enhancement of the mechanical stresses is accompanied by small perturbations of cell shape, but not by a significant change in cell size. We thus conclude that this live staining method enhances the cellular forces but only brings subtle shape alterations.