Fig. 6.

Substrate stress relaxation regulates filopodia dynamics. a, HT-1080 siR-actin labeled cells on fast and slow-relaxing substrates. Scale bar is 10 μm. Scale bar of time sequence of region of interest is 5 μm. b,c,d, Motor-clutch simulations of filopodia length and lifetime for fast and slow-relaxing substrates. Data compared to fast-relaxing hydrogel, Kolmogorov-Smirnov, two-sided, ****p<0.0001; n = 57, 68 (fast, slow) cells examined over 20 independent simulations. e,f,g, Quantification of filopodia length and lifetime for fast and slow-relaxing substrates from experiments with siR-actin labeled HT-1080 cells. Data compared to fast-relaxing hydrogel, Kolmogorov-Smirnov, two-sided, for filopodia length and lifetime, ***p=0.0006, ****p<0.0001; n = 41, 34 (fast, slow) cells examined over 2 independent samples. All statistical tests two-sided. d,g, r is Pearson correlation coefficient. h, Schematic highlights effect of substrate stress relaxation on cell migration in current work. White region: non-motile cells; blue region: motile cells. Cell-substrate bonds experience a faster loading rate on slow relaxing substrates relative to fast relaxing substrates resulting in a shorter lifetime and fewer bonds. The short bond lifetime causes smaller adhesion and reduced filopodia lifetime, allowing cells to change migration direction more frequently. This reduces the persistence of cell migration and impairs migration.