Figure 6. Sept9_i2 is incorporated into short septin filaments.

(a) Septin 2 and 9 co-localization indicative of septin polymers was assessed in in MCF7 cells stably expressing Sept9_i1,_i2 or_i3. GFP-Sept9_i1 was incorporated in long Sept2-filaments (mainly aligned with microtubules as depicted in Supplementary Fig. S4). GFP-Sept9_i2 was incorporated in very short and disorganized Sept2-filaments (aligned with actin fibers as depicted in Supplementary Fig. S5). GFP-Sept9_i3 was incorporated in long Sept2-filaments (aligned with actin fibers as depicted in Supplementary Fig. S5). White arrowheads point to septin filaments in cells negative for GFP-Sept9_i2 expression (delimited by dashed white lines). Framed regions are zoomed at the bottom of each image. White bars correspond to 10 μm and 5 μm in image and zoomed regions, respectively. (b) HUVEC cells, which expressed only the Sept9_i2 long isoform as indicated by Western blotting (left panel). Immunolabeling with pan-Sept9 antibody showed that Sept9_i2 was concentrated in very small clusters associated with actin stress fibers. White bars correspond to 10 μm.