Endocytosis of elongated tubules in the growth cone periphery. (A) Time-lapse confocal images of FM 5-95 internalization show immediate dye incorporation into an elongated tubule (yellow static arrow) near the base of a filopodium. In subsequent frames, the endocytic tubule is transported retrogradely toward the growth cone central domain. The boxed area is magnified in the panels at the right and the time after the initial membrane labeling (minutes:seconds) is indicated in each frame. See Additional file 8. (B) Time-lapse confocal images of fluorescent dextran internalization show similar endocytosis of an elongated tubule (red arrows) near the base of a filopodium. The focal pulse (10 s) of fluorescent dextran was applied at 0:00 and the initial frame shows nascent endocytic vesicles immediately after the removal of uninternalized dextran (0:15). Endocytic vesicles originating in the peripheral domain move retrogradely and fuse with other dextran-containing vesicles near the transitional- or central domains of the growth cone within one minute. See Additional file 12. Scale bars, 5 μm (left), 1 μm (right).