Fig. 7

Filament extension rate is decreased during invasive growth. a A PDMS substrate stiffness limit for filament penetration. Percentage of invading cells from time-lapse experiments (4 independent experiments for each PDMS stiffness, Young’s modulus indicated, 40:1 and 30:1) was quantified (n = 50–60 cells per determination from a total of 900–1200 cells) using wide-field microscopy. Bars indicate SD and ****p < 0.0001. b Filament extension rate is linear during surface and invasive growth. Cells grown on or in PDMS at indicated stiffness (35:1 and 40:1) over 2 h, with images every 5 min. Filament length was determined from the sum projection GFP images and normalized to an initial length of 10–12 μm. c Filament extension rate is reduced upon invasive growth. The extension rate was determined from the time-lapse acquisition of cells grown within PDMS at indicated stiffness (35:1 and 40:1). Surface growth was carried out on PDMS with a stiffness 190-85 kPa (30:1–40:1). Quantification from 2 to 4 independent experiments, n = 20–30 cells per PDMS stiffness. Bars indicate SD with ****p < 0.0001 and *p < 0.05. d Invasively growing filaments do not undergo substantial changes in the z-position. Cells expressing plasma membrane GFP were imaged (green; middle panel) after growth in ~ 150 kPa PDMS (35:1), chambers that were labeled with Alexa-633 ConA (magenta; left panel), and 100 × 0.2 μm z-sections were acquired with DIC image shown (right panel). XY (upper panels) and XZ maximum projections are shown with dotted lines indicating the upper and lower limits of the microchamber and the green arrow indicating the center in the z-axis of the filament tip