Emergence of Large-Scale Cell Morphology and Movement from Local Actin Filament Growth Dynamics
(A) The distributions of VASP (gray line in the graph) and F-actin (black line in the graph) were measured along the length of the leading edge of cells (position indicated by the arrow). The cell shown has VASP enriched at its smooth leading edge (VASP peak-to-base ratio = 1.84). The distribution of F-actin along the leading edge of this smooth cell is peaked in the middle and strongly correlates with that of VASP (r2 = 0.82, p < 0.0001). Scale bar = 20 μm.
(B) A keratocyte with rough leading edge and very weak VASP at the leading edge (VASP peak-to-base ratio = 0.76) has a very flat distribution of VASP (gray line in the graph) and F-actin (solid black line in the graph) measured along the leading edge (arrow). The distributions of VASP and F-actin along the leading edge of this cell strongly correlate with each other (r2 = 0.81, p < 0.0001). Additionally, the distributions of VASP and F-actin of the entire population of keratocytes strongly correlate (<r> = 0.71, SD = 0.23, p < 0.0001, n = 43).
(C) The F-actin density along the leading edge of a representative coherent cell with high VASP peak-to-base ratio—2.79 (gray line)—is increased compared to that of a decoherent cell with low VASP peak-to-base ratio—1.13 (black line). Mean intensity values are not normalized and were obtained from keratocytes imaged from the same coverslip. F-actin distributions between different cells were compared by calculating a ratio (F-actin peak ratio) of the mean F-actin intensity values from the middle half of the leading edge (0.25 to 0.75 position along the edge, indicated by the thick regions of each line in the graph), which generally correspond to the highest intensity values in peaked F-actin distributions, to the mean of the F-actin values from the rest of the leading edge (positions 0 to 0.25 and 0.75 to 1.00 along the edge, indicated by the thin regions of each line). Cells with peaked F-actin distributions had larger F-actin peak ratios than did cells with flat distributions. The F-actin peak ratio of the coherent cell (gray line) is 1.45, whereas that of the decoherent cell (black line) is 0.94. Also compare the cells in (A) and (B), which have F-actin peak ratios of 1.56 and 0.94, respectively.
(D) VASP peak-to-base ratios significantly correlate with F-actin peak ratios (r2 = 0.31, p = 0.0001, n = 43, solid line).
(E, F) For comparisons of F-actin and Arp3, mean intensity values were measured along lines (∼0.5 μm wide) positioned along the leading edge of keratocytes, immediately interior to cell edge. Anti-Arp3 mean fluorescence intensities measured along the leading edge of keratocytes are consistent with those of F-actin. A representative smooth cell (E) exhibits peaked Arp3 and F-actin distributions along the leading edge while a rough cell (F) has flat distributions. Scale bar = 10 μm.