Harnessing actin dynamics for endocytic trafficking

Abstract

Until recently, the actin cytoskeleton and the endocytic machinery were thought to operate independently. However, the actin cytoskeleton is an integral part of the cell cortex and there is growing evidence in diverse eukaryotes that F‐actin plays a direct role during endocytic internalization. Genetic studies in Saccharomyces cerevisiae have demonstrated that Arp2/3‐mediated F‐actin assembly is required specifically for the internalization step of endocytosis. Using real‐time image analysis, we recently defined a pathway for receptor‐mediated endocytosis in budding yeast. We have extended this analysis to the functions of some 60 proteins, and have analyzed the dynamic appearance, movement and disappearance of about 30 proteins at endocytic sites. A major conclusion of this work is that the proteins analyzed to date can be grouped into four functional modules involved in endocytic internalization. We are now analyzing in depth the molecular mechanisms responsible for actin's endocytic role. For example, we are performing experiments to distinguish the contributions of actin assembly versus myosin motor activity to endocytic internalization forces, and the specific roles of different activators of the Arp2/3 complex.