Imaging endocytic clathrin structures in living cells.

Our understanding of the clathrin-dependent endocytic pathway owes much to new visualization techniques. Budding coated pits and clathrin-coated structures are transient molecular machines with distinctive morphological characteristics, and fluorescently labeled versions of a variety of marker proteins have given us a tantalizing glimpse of the dynamics of the system in living cells. Recent live-cell imaging studies have revealed unexpected modes of coat assembly, with distinct kinetics, distinct recruitment of associated proteins, distinct requirements for the participation of actin and its accessory proteins, and apparently distinct mechanisms of membrane deformation. A crucial issue is to connect the events detected by light microscopy with the structures and properties of the molecular constituents. Here, I outline descriptions of coat assembly in different circumstances that are consistent with what is known from X-ray crystallography and electron microscopy.