Composite image of slices from several tomograms. Tomograms collected following treatment with AuNP-FGF21 for 1 h at 4°C, show (a) a lamellopodium decorated with clusters of AuNP pairs, (b) AuNP pairs clustered (right panel) on top of an invaginated membrane (middle panel) above a clathrin pit (left panel), and (c) a clathrin-coated vesicle; left panel showing AuNP pairs inside the vesicle, and right panel showing the clathrin cage. (d) Tomogram after 1 h treatment at 37°C, shows an endosome, tightly associated with actin filaments, with AuNP pairs inside, and (e) a vesicle presumably dividing, although merging cannot be ruled out. (f) Tomogram following overnight treatment at 37°C, shows a microtubule between a MVB, with unpaired AuNP inside (right panel) and other vesicle, with no AuNPs inside (putative late endosome). (For a complete mapping of AuNPs see Figure 4). AuNPs indicated by yellow arrows.