Differential requirements for actin during yeast and mammalian endocytosis

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Abstract
The actin cytoskleteon is essential for endocytosis in budding yeast but it is less significant in mammalian cells. Actin is shown to be required during plasma membrane invagination in yeast endocytosis due to the turgor pressure that is characteristic of yeast cells Key features of clathrin-mediated endocytosis have been conserved across evolution. However, endocytosis in Saccharomyces cerevisiae is completely dependent on a functional actin cytoskeleton, whereas actin appears to be less critical in mammalian cell endocytosis. We reveal that the fundamental requirement for actin in the early stages of yeast endocytosis is to provide a strong framework to support the force generation needed 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 in normal endocytosis. Conversely, increased turgor pressure in specific yeast mutants correlated with a decreased rate of endocytic patch invagination.