Figure 2. Anterograde and retrograde comets originate from specific sites within the dendritic arbor.

EB1-GFP comets growing anterogradely into a branch primarily originate from one of three sources: a parent branch, within the branch, or a branchpoint. Black arrows indicate the direction of the soma or distal tip for each montage. (A) EB1-GFP comets can be directed from the parent branch into a smaller branch. The red arrow identifies a comet that is guided into the smaller daughter branch from the parent branch, while the blue arrow follows a comet that bypasses the daughter branch. The red arrow in the corresponding kymograph indicates the point at which three comets are directed into the daughter branch. (B) Anterograde comets can originate from a specific branchpoint structure of a nascent branch. Red arrows indicate the branchpoint site of nucleation in both the montage and kymograph. (C) Anterograde comets originating within a branch also grow from specific sites (See also Movie S1). The orange arrows point to the identical origin of multiple EB1 comets. (D) and (E) Bar graphs depicting the percent of total anterograde comets that originate from each source, and that the source of EB1 comets for a branch depends on its length. (F) Retrograde EB1-GFP comets growing from a terminal branch originate from one of two sources: within the branch or from the distal tip (light and dark blue arrows, respectively in the montage and kymograph) (See also Figure S2). (G) and (H) Bar graphs depicting the percent of total retrograde comets that originate from each source, and that the source of EB1 comets for a branch depends on its length. Montage scale bars are 3 μm. Kymograph scale bars are 5 μm (x axis) and 30 s (y axis) for (A) and (C), 1.5 μm and 20 s for (B), and 2 μm and 30 s for (F). Data are means ± s.e.m.; n = 26 neurons and 133 comets for anterograde quantification and 21 neurons and 50 comets for retrograde quantification.