Under Pressure: the Differential Requirements for Actin during Yeast and Mammalian Endocytosis

Key features of clathrin-mediated endocytosis have been conserved across evolution. However, endocytosis in Saccharomyces cerevisiae is completely dependent on a functional actin cytoskeleton, while actin appears to be less critical in mammalian cell endocytosis. We reveal that the fundamental requirement for actin in early stages of yeast endocytosis is to provide a strong framework to support force generation required to direct the invaginating plasma membrane into the cell against turgor pressure. By providing osmotic support, pressure differences across the plasma membrane were removed and this reduced the requirement for actin-bundling proteins required for normal endocytosis. Conversely, increased turgor pressure in specific yeast mutants correlated with decreased rate of endocytic patch invagination.