The actin cytoskeleton at the leading edge of MDA-MB-231 is characterized by a high mobile fraction and dynamics.

<p>A) MDA-MB-231 cells transfected with GFP-actin, double stained with Phalloidin-Alexa 594 (a). Actin fluorescence accumulates mainly at the leading edge area. Scale bar 5 µm. Notice that MDA-MB-231 cells have a conspicuous lack of actin stress fibers. Rigth: Detailed section of the leading edge, showing the accumulation of GFP-actin (b) and actin filaments (c). Scale bar 2 µm. B) Representative picture frames from sequential FRAP experiments. Before FRAP (pre-bleaching), after high-intensity laser exposure (bleaching), during the initial phase of recovery (5 s) and at the end of the stable part of the curve (30 s). The bleached leading edge area is indicated by the white box (4×6 µm). C) Example of a FRAP experiment; fluorescence recovers to an average value of 71.5±4% following a monoexponential time course (fit depicted by a red dotted line). Incubation with cytochalasin D (90 nM) inhibits fluorescence recovery (CytD). D) Summary graph of the mean mobile fractions from MDA-MB-231 cells. Stable transfected cells (s, n = 44), high GFP-actin expressers (high, n = 10), low GFP-actin expressers (low, n = 10) and transiently transfected cells (231t, n = 6). Mean values of mobile fraction do not show statistical differences under any experimental conditions when compared with the stable transfected cell line (Student's t-test).