Cycles of periodic protrusions and retractions of a lamellipodium in the proximity of maturing filopodia adhesions.

<p><b>A.</b> The β3-integrin-EGFP (green) expressing REF52 fibroblast on a FN coated glass surface was time-lapse tracked with confocal microscopy. The cell membrane was stained by the fluorophore DiI (red). <b>B.</b> Magnified views of the white rectangle region in A showed the filopodia adhesion at the start (left) and end (right) of the time-lapse tracking sequence (20 min–47 min after seeding, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107097#pone.0107097.s008" target="_blank">Video S3</a>). <b>C.</b> Time-lapse montages of the white rectangle region in A. At the time point indicated by the grey asterisk, we had to increase the laser (488 nm) intensity to compensate for photobleaching. To better visualize lamellipodium activities, the presented montage was stretched vertically 2×. <b>D.</b> Histograms of the distances, durations and speeds of the cyclic protrusions (black bars) and retractions (brown bars) of lamellipodia in proximity to filopodia adhesions. Values in the parenthesis gave the number of measurements (at 14 filopodia adhesions in 5 cells). Scale bars: 1 µm (B), 10 µm (A). The horizontal grey bar indicates the width of a single image frame in the montage in C (2.5 µm).