Figure 1.

Matrix interaction defines individual motility of B lymphocytes. (A) JY cells were seeded at low density (40 cells mm⁻²) over 1,5 μg ml⁻¹ collagen IV or 10 μg ml⁻¹ fibronectin and imaged after 2 h with combined widefield and TIRF illumination to reveal LifeAct-GFP, respectively throughout the cell body and at the cell/matrix interface. Scale bar, 10 μm. (B) The proportion of the surface of LifeAct-GFP detected in the TIRF versus widefield images was measured for each cell (collagen IV, 87 cells; fibronectin, 101 cells; data pooled from 3 independent experiments). Bars show mean values. ***p < 0.001, Student-t test. (C) Cell shape volatility represents the standard deviation of each cell aspect ratio changes over consecutive frames (track length, 20 min; time interval, 1 min) over collagen IV and fibronectin (respectively, 23 and 25 cells; data pooled from 3 independent experiments). Bars show mean values. **p < 0.01, Student-t test. (D) JY cells were recorded after 2 h of seeding for 12 h at 12 frames min⁻¹. Images show representative 1-h tracks with color-coded speed (displacement over 1-min intervals). Scale bar, 100 μm. (E) One-hour tracks of 40 cells per condition were normalized to their x,y starting location and color-coded for their speed. (F) To quantify diffusion properties, the mean square displacement was plotted as a function of time interval (1-min increment). Data stem from 318 cell tracks on collagen IV and 1700 cell tracks on fibronectin. Diffusion coefficient D was calculated as the slope of the curve. See also Supplementary Figures S1 and S2 and Video S1.