Filament-forming cytoskeletal GTPase. Forms a filamentous structure with SEPTIN12; SEPTIN6; SEPTIN2 and probably SEPTIN4 at the sperm annulus which is required for the structural integrity and motility of the sperm tail during postmeiotic differentiation (PubMed:25588830). Required for normal organization of the actin cytoskeleton. Plays a role in the biogenesis of polarized columnar-shaped epithelium by maintaining polyglutamylated microtubules; thus facilitating efficient vesicle transport; and by impeding MAP4 binding to tubulin. Required for the progression through mitosis. Forms a scaffold at the midplane of the mitotic splindle required to maintain CENPE localization at kinetochores and consequently chromosome congression. During anaphase; may be required for chromosome segregation and spindle elongation. Plays a role in ciliogenesis and collective cell movements. In cilia; required for the integrity of the diffusion barrier at the base of the primary cilium that prevents diffusion of transmembrane prot