Actin blob prelocalization to future branching sites. (A) Time series of images show the movement of an actin blob (green; indicated by yellow arrowheads) in anterograde direction (0–149 s), stalling (298 s), and the emergence of a new branch (317 s) indicated by white arrowheads with dendrites labeled in magenta (Video 6). (B) The actin blob moves out of a retracting dendrite (0–93 s) and stalls (168–409 s) until the emergence of new dendrite (447 s). The retracting dendrite is marked with asterisks, and a newly emerging dendrite is marked by a white arrowhead (Video 7). (C) Two actin blobs (one indicated by yellow arrowheads, and one by yellow arrows) merge at the stalling site (452 s) to induce dendrite emergence (white arrowhead at 657 s and 838 s). The retracting dendrite is marked with asterisks (Video 8). (D) F-actin accumulation (yellow arrowheads in 91–226 s) until a new dendrite emerges (white arrowhead at 861 s; Video 9). (E) Bar graph shows the distribution of actin blob stalling times before branch emergence from 41 stalling/branching events in 10 neurons from seven experiments.