Definition of metrics used to characterize clathrin-coated structures. (A) Schematic representation of the timeline to describe the formation of a clathrin-coated pit mediated by the assembly of the clathrin coat (Kirchhausen et al., 2014). The last step mediated by fission of the membrane neck connecting the mature coated pit from the originating membrane results in formation of the fully formed coated vesicle. Metrics of neck width, pit height, full width at half maximum, and major and minor axis of the fitted ellipse used to morphologically describe the clathrin-coated pits are shown. (B) Metrics used to characterize clathrin-coated vesicles. (C) Example of a single plane from a selected endocytic clathrin-coated pit in a cell prepared by HPFS and imaged by FIB-SEM at ∼5 nm isotropic resolution. The darker voxels corresponding to the deformed membrane and the coat surrounding the pit (left panel) were segmented using an Otsu-based intensity threshold approach (Otsu, 1979) to generate a skeletonized binary mask (central panel) which was then used to fit the ellipse (right panel).