Endocytic Clathrin Coats Develop Curvature at Early Stages of Their Formation

Sculpting a flat patch of membrane into an endocytic vesicle requires curvature generation on the cell surface, which is the primary function of endocytic protein complexes. The mechanism through which membrane curvature is imposed during formation of clathrin-coated vesicles is an ongoing controversy. Using super-resolved live cell fluorescence imaging, we demonstrate that curvature generation by clathrin-coated pits can be detected in real time within cultured cells and tissues of developing metazoan organisms. We found that the footprint of clathrin coats increase monotonically during formation of curved pits at different levels of plasma membrane tension. These findings are only compatible with models that predict curvature generation at early stages of endocytic clathrin-coated pit formation. Therefore, curvature generation by clathrin coats does not necessitate a dynamically unstable clathrin lattice that would allow an abrupt flat-to-curved transition.