Small endocytic vesicle hot-spots at the lateral margins of lamellipodia. (A) Time-lapse confocal images of FM 5-95 internalization show endocytosis at the lateral margin of a lamellipodium as the growth cone narrows. The boxed area is magnified in the panels on the right and the time after the initial membrane labeling (minutes:seconds) is indicated in each frame. The static dashed line represents the lamellipodial margin at t = 0:07. In subsequent frames, the lamellipodium remodels to form a dye-rich membrane ruffle (red arrows, 0:19, 0:21). Within seconds, numerous small vesicles form (yellow arrowheads, frames 0:22, 0:23). The corresponding time-lapse movie is shown in Additional file 2. (B) Similar ridge formation at a lamellipodial lateral margin observed by time-lapse DIC microscopy. See Additional file 3 for the corresponding time-lapse movie. Scale bars, 5 μm (left), 1 μm (right).