Figure 4.

Density and spatial distribution of actin nodes. A, The node rank counts the number of branches that meet at anode. B, Node rank prevalence (for rank >2), calculated for the entire population (mean and STD). C, Nearest neighbor analysis of branch ends within 10 nm of a membrane. The mean nearest neighbor distance between branch ends is slightly smaller than if they were randomly placed (p = 0.02). D, Pairwise comparisons of the rank-3 node density. Bar plots show mean and STD. The surface-to-volume ratio is a good predictor of the average node density within a spine (Extended Data Fig. 4-1). E, Rank-3 node density for the entire population, shown separately for head and neck regions. Sample size indicated by gray numbers. F–I, Spatial density of rank 3 (F), rank 4 (G), nodes of rank >4 (H), and branch ends (I) as a function of their distance to the nearest membrane given by the distance transform (Fig. 3E). The node density is constant throughout the inner regions and drops near the boundary. Branch ends are preferentially found close to the membrane. Lines indicate mean values and colored regions the STD.