Septins: one ring to bind them

The cytoskeleton is composed of dynamic polymers of actin, tubulin, and intermediate filaments. These proteins are responsible for maintaining cell shape, intracellular organization and transport, cell division, and many other cellular processes. Among the cytoskeletal interacting proteins are septins, a conserved family of GTP binding proteins that polymerize into higher ordered filaments. Septins interact with and regulate the dynamics of both actin and microtubule cytoskeletons. Septins also regulate the processes of cytokinesis and exocytosis. In this study we use COS-7 cells as a model for studying the localization, interaction, and dynamics of SEPT2 and SEPT7. We demonstrate that septins form filaments that colocalize with actin filaments in the cell periphery. Further, we show that actin filaments, but not microtubules, are required for formation of septin filaments in vivo.