Figure 4. EGFP-ZBP1 Forms Granules which Exhibit Dynamic Anterograde and Retrograde Movements within Live Neurons

(A) EGFP-ZBP1 was observed in the form of granules (displayed in black) that were distributed throughout the neurites. Two regions of interest are indicated within blue (RI) and magenta (RII) boxes.

(B) Higher magnification view of RI. EGFP-ZBP1 granules were noted of varying sizes. The larger granules frequently were stationary or oscillatory, and accumulated at branch points or bifurcations between neurites (white arrows). The smaller granules were more motile, and exhibited dynamic anterograde and retrograde movements. Six motile granules were tracked in a short neurite which projected from the bifurcation (1–6, blue arrows; see also Movie 1 as supplemental data). Three other granules were tracked in an adjacent neurite (7–9, blue arrows). The arrows indicate the net direction of each trajectory.

(C) Higher magnification view of RII shows four granules (1–4, magenta arrows) that were tracked in a retrograde direction.

(D and E) Examples of EGFP-ZBP1 granule (shown in green) movements from (B) with high temporal resolution. (D) Granule 1, anterograde movement, white arrow indicates initial location, green arrow movement at depicted times. (E) Granule 2, retrograde movement, red arrow indicates movement at depicted times.

(F) EGFP-ZBP1 granules exhibiting bidirectional movements. Instantaneous velocities (between two consecutive frames) of each granule were plotted versus the time period that the granule could be tracked (movements of six granules are plotted).