Figure 1

The stages of clathrin-coated vesicle formation. (A) Inititation and early invagination: a clathrin-coated pit is formed and cargo-specific adaptors are selected. Late invagination: further clathrin is recruited and polymerizes in hexagons and pentagons to form the clathrin coat. Constriction: dynamin is recruited to the neck of the forming vesicle where it forms helical structures, and induces membrane scission. Fission: an endocytic vesicle is produced containing cargo molecules. Dynasore inhibits the GTPase activity of dynamin, blocking constriction and fission. (B) The steps leading to macropinocytosis. During the vesicular trafficking process, cellular membranes undergo dynamic morphological changes, in particular at the vesicle generation and fusion steps. Macropinocytosis involves the eruption of membrane ruffles from the cell surface that can fuse with the plasma membrane to engulf surrounding cargo, a process that requires extensive actin mobilization. Macropinosomes then fuse with compartments of the normal endocytic pathway. Dynasore reduces plasma membrane cholesterol, inhibiting mobilization of the cellular membrane.