Proteins enriched in FIT2-induced ER bubbles. (A) COS-7 cells were transfected with FIT2-HA and stained with anti-HA antibodies and LipidTOX. Representative images were captured by 3D-SIM. A lateral view of a 3D bubble-like structure is shown on the right. Scale bars, 10 µm. (B) COS-7 cells were cotransfected with FIT2-HA and the indicated ER tubule proteins and stained with anti-HA antibodies alone or together with anti-Myc antibodies. Representative images were captured by 3D-SIM. Lateral views of 3D bubble-like structures are shown on the right. Scale bars, 10 µm. (C) As in B, but with COS-7 cells coexpressing FIT2-HA and Flag–Climp-63. The insets show magnified details in white squares. Scale bars: 10 µm; 2 µm (inset). (D and E) Distribution of endogenous septin 2 filaments (red) visualized in COS-7 cells expressing FIT2-HA (green). The bottom images show enlargements of the boxed regions on FIT2-induced ER bubbles. The line scans of the red and green fluorescence intensities indicate the colocalization of septin 2 filaments and FIT2-induced ER bubbles. Scale bar, 10 µm; 2 µm (inset).