Differential requirements for actin during yeast and mammalian endocytosis

Abstract

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.

Endocytic Accessory Factors and Regulation of Clathrin-Mediated Endocytosis

“…This may be attributable to physical constraints placed on the endocytic machinery in these two very different types of cells. For instance, it has been proposed that actin plays an obligatory role in walled yeast endocytosis because high membrane tension resulting from turgor pressure elicits more work to invaginate the membrane as compared with mammalian cells (Meckel et al 2004;Aghamohammadzadeh and Ayscough 2009;Boulant et al 2011). Indeed, there is evidence that membrane tension may modulate the requirement for actin in mammalian CME and yeast protoplasts wherein regimes of high membrane tension, generated by hyperosmotic challenge or physical stretching, invoke a requirement for actin (Aghamohammadzadeh and Ayscough 2009;Boulant et al 2011).…”

A High Precision Survey of the Molecular Dynamics of Mammalian Clathrin-Mediated Endocytosis

“…The fact that other proteins such as the BAR domain proteins endophilin2 or BIN1 were detected at only a subset of scission events suggests that there were inherent limitations of recruitment detection, since these proteins are thought to be essential for scission [9,54]. However, it remains possible that there were genuine molecular differences between scission events, perhaps through the influence of other types of (unlabelled) receptor cargo [63], in response to changes in physical parameters, such as membrane tension [69] or because of genuine underlying variability in the core mechanism of CME [53]. Nonetheless, and based on the data presented here, at optical resolution potential molecular differences between scission events in NIH-3T3 cells did not correlate with obvious differences in CCS behaviour.…”

Proteins with prion-like domains can form viscoelastic condensates that enable membrane remodeling and endocytosis

“…One such process is clathrin-mediated endocytosis 38 (CME) a fundamental mechanism of cell surface membrane receptor turnover and recycling, 39 nutrient uptake and synaptic vesicle regeneration, among others (Conner and Schmid 2003). The 40 mechanism of membrane invagination in CME has most convincingly been demonstrated to be 41 growth of membrane-bound branched actin, however CME has also been shown to occur under 42 conditions where actin polymerization is absent and the mechanisms by which this happens 43 remain unclear (Aghamohammadzadeh andAyscough 2009, Li, Shao et al 2015).…”

“…If, however, turgor pressure is eliminated, CME can also occur independent 58 of actin polymerization (Aghamohammadzadeh andAyscough 2009, Li, Shao et al 2015).…”