Septin filament organization models and corresponding changes in dipole orientation. (A) Representations of a single septin protofilament shown associated with the cortex (blue) with the conGFP-tagged septin (green) shown with a possible GFP dipole orientation (black). C-terminal coiled-coil domains are shown as rectangles extending from the three septins that are predicted to have these domains. The left and right half of a filament are related by a 180° rotation around a vertical axis shown in the side view as a dotted line and red arrow. The summed angle for all possible dipole orientations is noted on the right. (B) Representations of paired septin filaments. Top and bottom filaments are related by a 180° rotation around a horizontal axis. The summed angle for all possible dipole orientations is noted on the right. (C) Paired filament models show polymerization of filament if it processes straight or twisted relative to the cortex. Corresponding dipole angles of tagged subunits are represented by the arrows. (D) The same filament procession and relative dipole angles that could be captured in the axial resolution of a 1.4 NA objective (∼500 nm) when viewed in cross section. The dipole orientations for each organizational scenario is shown below the filament and noted for anisotropy. (E) Model for filament organization in the S. cerevisiae hourglass (left), transition (middle), and split ring (right) states that is consistent with anisotropy measurements through time.