Septins localize to macropinosomes and their contact/fusion sites. (A) Confocal images of MDCKs stained for SEPT2 and F-actin with or without treatment with 0.1% Triton X-100 before fixation. (B) Bar graph shows the sum intensity (mean ± SEM) of SEPT2 per cell area (n = 15). AU, arbitrary units. (C and D) 3D-rendered confocal microscopy (C) and SIM (D) images of MDCK-PM-mCherry cells stained for endogenous SEPT2. Dashed lines outline the cell edge, and arrows point to SEPT2 at the contact sites of macropinocytic vacuoles. (E) MDCK-PM-mCherry cells were incubated with FITC-dextran and stained for SEPT2. 3D-rendered confocal images show SEPT2 at the periphery and in between (arrow) macropinosomes/endosomes. (F) MDCK-PM-mCherry cells were transfected with SEPT2-GFP and imaged live with wide-field deconvolution microscopy. Still frames show SEPT2 accumulation (arrows) at the site of fusion between two macropinosomes.