Fluid-phase uptake by macropinocytosis in Dictyostelium.
To study fluid-phase endocytosis in living cells and its relationship to changes in the cell cortex, we have used a green fluorescent protein (GFP)-tagged version of coronin, an actin-associated protein that localises to dynamic regions of the Dictyostelium cell cortex. In the confocal microscope, internalisation of fluorescently labelled dextran as a fluid-phase marker can be recorded simultaneously with the recruitment of the coronin-GFP fusion-protein from the cytoplasm of the phagocyte. At crown-shaped surface protrusions, extracellular medium is taken up into vesicles with an average diameter of 1.6 microns, which is significantly larger than the 0.1 microns diameter of clathrin-coated pinosomes. The observed frequency of macropinosome formation can account for a large portion, if not all, of the fluid-phase uptake. The redistribution of coronin-GFP strongly resembles cytoskeletal rearrangements during phagocytosis. Scanning-electron micrographs indicate that crown-shaped cell-surface extensions can undergo shape changes, without a particle bound, that are similar to shape changes that occur during phagocytosis. In quantitative assays, the uptake of particles and fluid are about equally dependent on F-actin and coronin.
Hacker
U
U
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Albrecht
R
R
Maniak
M
M
D000199:Actins / Q000378:metabolism*; D000818:Animals; D004023:Dictyostelium / Q000502:physiology*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000493:pharmacokinetics; D008840:Microfilament Proteins / Q000235:genetics / Q000493:pharmacokinetics*; D010873:Pinocytosis; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000493:pharmacokinetics
D000199:Actins; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; C072061:coronin proteins; D049452:Green Fluorescent Proteins