Figure 7.

Endosome-endosome fusion. Wild-type cells were fed with rhodamine-green dextran for 30 min and briefly washed with buffer; time-lapse series were recorded with TIRM. The cell boundaries are outlined in the first frame. (A) Two bigger vacuoles that moved together through the cell for some minutes finally fused with each other (arrowheads). The accompanying Movie 6 shows a longer time course (252 s) of the same cell. (B) A big vacuole (asterisk and then arrowhead), that was barely visible in the first frames, repeatedly fused with small vesicles, and thereby was slowly filled with fluid phase marker in roughly 4 min. (C) Higher magnification of the vacuole marked in B, small vesicles fusing with this vacuole are marked by arrowheads. The accompanying Movie 7 shows a longer time course (242 s) of the same cell. The movies play at 6 fps; bars, 2 μm (A), 5 μm (C), and 10 μm (B). (C) Ultrastructure of fusion events between endocytic vacuoles in wild-type D. discoideum cells (arrowheads). Note the plumes of differentially electron-dense lumenal material (arrows) diffusing through some of the fusion pores. M, mitochondria. Bar, 1 μm.