Circulation of the plasma membrane in Dictyostelium

We have developed a fluorimetric assay with the use of the dye FM1-43 to determine the rate at which Dictyostelium amoebae endocytose their surface membrane. Our results show that they do so about once each 4-10 min. A clathrin null mutant takes its surface up only similar to 30% more slowly, showing that this membrane uptake cannot be caused by clathrin-coated vesicles. Surprisingly, Ax2 and its parent, NC4, which differ in their rates of fluid-phase internalization by similar to 60-fold, take up their surfaces at the same rates. These results show that,in axenic cells, the uptake of fluid and Of surface area are separate processes. The large activity: of this new endocytic cycle in both Ax2 and NC4 amoebae appears capable of delivering, sufficient new surface area to advance the cells' fronts during migration.