Figure 4

Small vesicle endocytic hot-spots triggered by filopodial - lamellipodial contacts. (A) Time-lapse confocal images of FM 5-95 internalization show a detached filopodium collapse atop the dorsal surface of the growth cone and trigger an endocytic hot-spot. The boxed region is magnified in the right panels and the time after the initial membrane labeling (minutes:seconds) is indicated in each frame. The dashed arrows (white) are static and indicate the initial position of the filopodium. The detached filopodium lifts out of the focal plane (0:15 to 0:20, red arrows) and within seconds collapses atop the growth cone body (yellow bracket, 0:21), eliciting a streak of small vesicles (yellow arrowheads, 0:22). See Additional file 4 for the corresponding time-lapse movie. (B) Time-lapse DIC images show a similar loss of filopodia atop the dorsal surface of the growth cone. Detached filopodia (blue and red arrows) approach lamellipodia and rapidly disappear. One filopodium (red arrow) lifts out of the focal plane (0:46 to 56), collapses atop a lamellipodium (0:58 to 1:06), and disappears as in (A). The corresponding time-lapse movie is shown in Additional file 5. Scale bars, 5 μm (left), 1 μm (right).