Dictyostelium AX2 cell expressing VatM-GFP viewed by fluorescence (green) and interference reflection microscopy (red). The interconversion of vacuolar and tubular elements can be seen as the vacuoles empty. The frames were collected at 1 second intervals.

Phagocytosis of yeast particles by Dictyostelium cells whose endosomes had previously been labeled with TRITC-dextran. The upper cell is ingesting a yeast particle on its left in the first frame; the yeast particle becomes surrounded by endosomes in subsequent frames. Arrows mark the appearance of TRITC-dextran at the bud neck, which is indicative of endosome fusion. In the meantime, the lower cell has also ingested a yeast particle (outlined). The phagosome containing this particle presently fuses with a pre-existing multi-particle phagosome. TRITC-dextran (arrow) collects at the site of fusion as well as at the bud neck. In the last frame (9 minutes after uptake), the VatM-GFP fluorescence in the membrane of the new phagosome resembles that of earlier phagosomes. Frames were collected at 5 second intervals.

Exocytosis of the indigestible remnants of a yeast particle. This Dictyostelium cell has two yeast-filled phagosomes with VatM-GFP-labeled membranes and a third phagosome that has no label (top). As the movie progresses, the focus is shifted from the upper region of the cell, where the phagosomes are located, to a plane close to the substratum, to reveal the bright labeling of the contractile vacuole system. Returning to the phagosome-rich focal plane, a ring of TRITC-dextran can be seen at the neck of the unlabeled phagosome, demonstrating that it is a late phagosome from which vacuolar proton pumps have been retrieved. A few frames later, the digested yeast particle is exocytosed. Frames were collected at 5 second intervals.

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