Filament-forming cytoskeletal GTPase (By similarity). May play a role in cytokinesis (Potential). Involved in spermatogenesis. Involved in the morphogenesis of sperm heads and the elongation of sperm tails probably implicating the association with alpha- and beta-tubulins. Forms a filamentous structure with SEPTIN7, 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 (By similarity). Septins polymerize into heterooligomeric protein complexes that form filaments, and can associate with cellular membranes, actin filaments and microtubules. GTPase activity is required for filament formation. Interacts with SEPTIN6 and SEPTIN11. Self-associates. Component of a octomeric complex consisting of SEPTIN12, SEPTIN7, SEPTIN6 and SEPTIN2 or SEPTIN4 in the order 12-7-6-2-2-6-7-12 or 12-7-6-4-4-6-7-12 and located in the sperm annulus; the octomer polymerizes into filaments via the SEPTIN12 N- and C-termini; the SEPTIN12:SEPTIN7 association is mediated by the GTP-binding domains. Interacts with SPAG4 and LMNB1. Associates with alpha- and beta-tubulins (By similarity). At interphase, forms a filamentous structure in the cytoplasm. During anaphase, translocates to the central spindle region and to the midbody during cytokinesis (By similarity). Found in the sperm annulus. Predominantly expressed in testis and epididymis. Component of the sperm tail annulus (at protein level). In developing testis, expression increases steadily until sexual maturity (approximately 49 days postpartum) where it remains expressed at a relatively constant level. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.