Endosome fusion and microtubule-based dynamics in the early endocytic pathway of dictyostelium.
Dictyostelium amoebae, like mammalian macrophages, take up fluid by macropinocytosis. The present study used fluorescent fluid-phase markers and GFP-labeled microtubules to visualize the uptake, dynamics, and fusion of early endosomes in Dictyostelium. Consecutive labeling with two fluorescent fluid-phase markers demonstrated that within the first few minutes after uptake, new macropinosomes underwent fusion with pre-existing endosomes. The fusing endosomes, which represent the mixing compartment, displayed extreme shape changes and rapid transport about the cell in association with microtubules. The great plasticity of endosomes at this stage of maturation was also evident by electron microscopy. The constant undulatory motion of microtubules was implemental in establishing contact with endosomes. Treatment of cells with agents that selectively disrupted either actin filaments or microtubules confirmed that endosome dynamics were microtubule based. Further maturation of endosomes led to loss of pleiomorphy in favor of a spherical shape, inability to fuse with new macropinosomes, and diminished motility.
Clarke
Margaret
M
Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA. clarkem@omrf.ouhsc.edu
Köhler
Jana
J
Heuser
John
J
Gerisch
Günther
G
D000199:Actins / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism* / Q000648:ultrastructure; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D006735:Horseradish Peroxidase / Q000378:metabolism / Q000493:pharmacokinetics; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D015739:Nocodazole / Q000494:pharmacology; D010873:Pinocytosis; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D014404:Tubulin / Q000378:metabolism
D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003911:Dextrans; D008164:Luminescent Proteins; D011500:Protein Synthesis Inhibitors; D013844:Thiazoles; D053778:Thiazolidines; D014404:Tubulin; D049452:Green Fluorescent Proteins; D006735:Horseradish Peroxidase; D015739:Nocodazole; C037067:latrunculin A