Figure 2

Decision making in the phagocytic response to positive and negative curvature. Fluorescence images of PHcrac-GFP (green) and mRFP-LimEΔ (red) are superimposed on greyscale brightfield images that show the shape of budded yeast particles. The two lobes of each particle are marked by dots or circles in the first and last frames of each series. Time is indicated in seconds. (a) Interplay of a Dictyostelium cell with a budded yeast, ending in severing of the particle. The cup extends halfway around the distal lobe of the particle (frame at 106 seconds) before retreating to the neck, where actin strongly accumulates (154 to 520 seconds). Finally, the particle is severed (544 to 729 seconds) and one lobe is internalized. (b) A similar sequence of events, but ending with complete uptake of the budded yeast labeled with dots. First, the cup extends up to part of the distal lobe (79 seconds). Subsequently the cup draws back to the neck of the particle (130 and 177 seconds) where actin strongly accumulates (445 seconds). Eventually the actin disassembles and the cup extends again (500 and 559 seconds), until the particle is completely engulfed (673 seconds). A third variant of interaction with a particle is exemplified by the budded yeast marked with circles at the left of the cell. Here the cup progresses continuously around the entire particle without a strong accumulation of actin at the neck. The complete series are shown in Additional files 2 and 3. Bar = 10 μm.