NBEAL2 and SEC22B are required for α-granule formation in imMKCL cells. Transmission electron micrographs of representative cells show abundant electron-dense α-granules (arrow heads in magnified insets) visible in WT (A) and empty lentiviral transduced (mock) (B) cells. Additional imMKCL cells are shown in supplemental Figure 4. α-granules were not observed in NBEAL2-KO (C) or SEC22B-KO (D) cells, indicating both proteins are required for granule formation (bars = 2 μm). Thin sections were cut and stained with uranyl acetate and lead citrate, and samples were examined with a JEOL JEM-1011 electron microscope at 80 kV. Images were captured with a side-mounted Advantage HR CCD camera.