Fig. 2: Nanocluster fusion is more stable in the circumferential direction.

a Time-lapse fluorescent images and binarized images of lifeact::GFP expressing tracheal cells with 0.32-s intervals at stage 15. The fusion sites of clusters were labeled with magenta (see Supplementary Fig. 2 and “Fusion stability”). The right-most images are the temporal projection of the six frames, color-coded with Spectrum. Upper: Actin pattern at −40 min. Actin nanoclusters change in shape and size dynamically. Lower: Actin pattern at 0* min. Although the circumferential cables become apparent, the cables are still unstable. Scale bar, 0.5 µm. b Duration of the fusion of the nanoclusters with respect to the orientation. The duration of circumferential fusion became significantly longer than that of the diagonal fusion at 0* min. 0° corresponds to the longitudinal axis, whereas 90° indicates the circumferential axis of the tube. The numbers of fusions (n) are written below. Boxplots represent the median (bar), mean (black diamond) plus minima and maxima with lower and upper quantiles. For statistical analysis, the two-sided Kruskal–Wallis test (shown in parentheses, P = 0.565 in −40 min, P = 0.322 in −30 min, P = 0.193 in −20 min, P = 0.0343 in −10 min, and P = 0.0382 in 0* min) followed by a pairwise comparison using the two-sided Wilcoxon rank-sum test with Bonferroni adjustment of the P value (shown with bar) was performed. ^∗P < 0.05. See “Fusion stability” for detail. c Model for actin nanocluster-to-cable transition. Through repetitive fusion and fission of the nanoclusters, circumferential fusion is slightly stabilized, thereby leading to circumferential cable formation in a steady state. Source data are provided as a Source Data file.