Figure 10

Myosin-II engagement in particle release. Cells interacting with budded yeast express GFP -myosin-II heavy chains (green) and the mRFP -LimEΔ label for filamentous actin (red). Positions of the yeast mother cells are indicated by open or closed circles. Time is indicated in seconds. (a) Complete uptake of a particle, showing no myosin-II associated with the phagocytic cup, except a slight enrichment at the plasma membrane when the phagosome is closing (109 seconds). The cell has a long tail rich in myosin-II, which is shown in full length during its retraction at 109 and 134 seconds. (b) Attempted uptake and release of a particle carrying a small bud pointing toward the cell. Myosin-II does not associate with the cup as long as it grows (30 and 71 seconds), but strongly accumulates during retraction of the cup and release of the particle (124 to 285 seconds). (c) Partial uptake of a yeast particle (open circles) showing no accumulation of myosin-II during extension of the cup (0 frame). Subsequently myosin-II is recruited to the plasma membrane surrounding the retracting cup (88 seconds, closed arrowheads), but even then not to the actin-rich neck region. Myosin-II accumulation is again observed during retraction of a second cup (closed circles). Finally, the second particle is engulfed by another cell, where myosin-II is again missing during cup extension (198 seconds). (d) Simultaneous release of one particle (closed circles) and partial uptake of another (open circles). Actin, which strongly accumulates at the neck of the first particle, is not accompanied by myosin-II (84 seconds, open arrowhead). Eventually, the second particle is also released. The enrichment of myosin-II in the retracting cups occurs asynchronously for the two particles. Bar = 10 μm for all images.