Figure 1

(a) Confocal fluorescence image of a GFP-actin transfected neuronal NG108-15 growth cone. The edge position was determined from each image by extracting a line profile along an angle dependent direction taken from the c.m. To get subpixel position resolution, a Gaussian function was fitted to the derivative of each of these line profiles (b). The fit properties were used to determine the reliability of the detection, visualized in (a) by white dots for unreliably detected and black for reliably detected edge positions. The 95% confidence interval for the fit gives an error of $<6\mathrm{nm}$.Reuse & Permissions

Figure 2

Statistics of lamellipodial fluctuations. (a) The measured velocity probability distribution (bars) of a growth cone typically shows two prominent protrusion and retraction velocities. For the fitting of the histogram, we assume a favored protrusion and retraction velocity, influenced by the inherent noise of a biological system. Thus, it is adequate to fit Gaussians to the histograms and we determined the respective maxima at $-2.36\pm 0.11\mu \mathrm{m}/\min$ (dotted line) and $2.42\pm 0.18\mu \mathrm{m}/\min$ (solid line) with the displayed fits. (b) presents a log plot of the residence time distribution (bars), and an exponential fit-function (solid line) $\mathrm{const}\times \exp (-r_{M}t)$, where $r_M$ denotes the measured decay rate and $t$ time. The decay rates in this example are $0.08\pm 0.01{\mathrm{s}}^{-1}$ for the retraction and $0.11\pm 0.01{\mathrm{s}}^{-1}$ for the protrusion. (Errors, and error bars represent the 95% confidence interval for fits used.)Reuse & Permissions

Figure 3

(a) Calculated potential using Eq. (4). The arrows visualize the stochastic switching between a retraction (left) and a protrusion (right) state. $\alpha$ and $\gamma$ denote the potential minima, and $\beta$ the potential maxima. The potential can be used to infer the noise parameter for switching from retraction to protrusion and vice versa. (b) The resulting noise parameters for 23 experiments. ${\eta }_{\mathrm{rp}}$ is presented by a circle and ${\eta }_{\mathrm{pr}}$ by a cross. [For better readability, one experiment with values ${\eta }_{\mathrm{rp}}=16.6\pm 8.2(\frac{\mu \mathrm{m}}{\min }{)}^2{\mathrm{s}}^{-1}$ and ${\eta }_{\mathrm{pr}}=15.2\pm 7.7(\frac{\mu \mathrm{m}}{\min }{)}^2{\mathrm{s}}^{-1}$ was omitted in the graph.]Reuse & Permissions

Figure 4

(a) Fluorescent image of a GFP-actin transfected growth cone, translocating in the direction of the arrow. The two marked areas, $\alpha$ and $\beta$, are independently analyzed, and the measured potentials are presented in (b). Whereas the potential perpendicular to the direction of growth (solid line) favors the retraction states, the potential in the direction of growth presents a tilted potential that favors the growth of the lamellipodium.Reuse & Permissions