Figure 3. The release of at least 20 Netrin-1 molecules is sufficient to induce filopodia growth.

(a) With 130 Netrin-1 molecules inside the vesicle (N_v = 130), after VB several new filopodia grew towards L_v (red arrows).(b) as in a but for N_v = 40. (c) as in a but for N_v = 20. (d) as in a but for N_v = 8. Black crosses indicate L_v (e) Collected data showing the relation between N_v and N_newfilo. The least square fit of the experimental data (red curve) with a straight line of parameters a = 1.24 and b = 0.045 (chi-square two-tailed significance = 0.05) suggests that the presence of approximately 22 Netrin-1 molecules inside vesicles are sufficient to drive the growth of a single filopodium. Data were confirmed by statistical significance. Note that the results of N = 14 control experiments are illustrated by mean value and dispersion bar. Scale bar: 10 µm.