Topography of Lipid Droplet-Associated Proteins: Insights from Freeze-Fracture Replica Immunogold Labeling

Figure 8

Freeze-fracture views of lipid droplet and ER membrane associations in lipid-laden macrophages immunogold-labeled for adipophilin. (a) ER membranes are visible in both P face and E face views. Moderate labeling is seen in the P faces of the ER membranes. (b) Lipid droplet closely associated with ER membranes. Abundant gold label marks the presence of adipophilin in the ER membrane immediately adjacent to the lipid droplet. In contrast, ER membranes adjacent to mitochondria (M) are devoid of label. (c) Lipid droplet situated in a cup formed from ER membranes. The lipid droplet has been convexly fractured and lies beneath (i.e., adjacent to and not within) both ER membranes exposed. (d) Similar view to (c) but with labeling for adipophilin using the FRIL technique. Abundant gold label marks the presence of adipophilin in the ER membrane (P face) immediately adjacent to the lipid droplet. Bars: 0.2 μm.