Imaging of CCPs by combined ICM and confocal microscopy and TEM. (A) Topographical image of a fixed Cos-7 cell (left) and corresponding fluorescent image (right) of the same clathrin-EGFP–transfected cell superimposed onto the topographical image but inverted and presented in a red palette, as previously described (Shevchuk et al., 2008). The image reveals that the pit topography matches the Clc-EGFP fluorescence. (B) Zoomed topographical and fluorescent images of the areas boxed in A show clathrin fluorescent signal associated with the protrusions on the cell surface. (C) TEM image of cell plasma membrane protrusion associated with a CCP in the Cos-7 cell. (D) A sequence of HPICM topographical images shows the formation of a protrusion before CCP closure in a Cos-7 cell. (E) A TEM image shows the protrusion of cell plasma membrane associated with CCP in an NIH 3T3 cell. (B–E) Red arrows point at membrane protrusions associated with CCPs. (F) A TEM image shows a CCP without distinct protrusion in an NIH 3T3 cell. (E and F) TEM images were reproduced with permission from Bretscher et al. (1980). (G) The sequence of HPICM topographical images shows CCP closure with the formation of a protrusion in an NIH 3T3 cell.