Endocytosis assays in intact and permeabilized cells.

Clathrin-coated pits and vesicles represent the major ports of entry into most eukaryotic cells. As well as performing housekeeping functions (e.g., allowing cells to take up essential nutrients), the endocytic pathway participates in a number of tissue-specific events such as synaptic-vesicle recycling, control of morphogen gradients during development, downregulation of receptor tyrosine kinases, and immune surveillance. To understand the role played by clathrin-mediated uptake, it is therefore essential to have robust endocytosis assays in intact cells. The clathrin-coated vesicle cycle requires a complicated interplay of proteins and lipids that is regulated in space and time. Reconstitution assays in permeabilized cells provide a powerful approach to understanding how this complex process is regulated.