Fig. 6. Relative dynamics of IRSp53 and WAVE2 in lamellipodia and filopodia. Panels show video frames of a B16 cell that was cotransfected with EGFP-IRSp53 and WAVE2-DsRed. Lamellipodium formation was induced by microinjection of constitutively active Rac1L61 a few minutes before imaging. (a) Fluorescence channel for EGFP-IRSp53; (b) fluorescence channel for WAVE2-DsRed; (c) phase contrast. Arrowheads indicate filopodium tip. Fluorescence intensity was measured between white and black brackets. The profiles of fluorescence intensity of the filopodium and lamellipodium are represented in the corresponding image as fil and lam, respectively. Arrow in the profile indicates the axis of fluorescence intensity. The fluorescence intensity of EGFP-IRSp53 at the filopodium tip decreases before retraction and for DsRed-WAVE2 only during retraction. Double arrowhead at time 1:24 indicates the tip position at 0:49. (d) The specific fluorescence intensity (I) at the tip was obtained by the subtraction of background fluorescence from the tip fluorescence. IR corresponds to the ratio between fluorescence intensities at n seconds (In) and that after i seconds (In+i). Time is in minutes and seconds. Bar, 10 µm. See supplementary video.