Filament-forming cytoskeletal GTPase (By similarity). 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 (PubMed:24213608). 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 (PubMed:25588830). May play a role in cytokinesis (Potential). 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 (By similarity). Interacts with SEPTIN6 and SEPTIN11. Self-associates. Component of a septin core 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 respective GTP-binding domains (PubMed:25588830). Interacts with SPAG4 and LMNB1 (PubMed:25775403). Associates with alpha- and beta-tubulins (PubMed:24213608). At interphase, forms a filamentous structure in the cytoplasm. During anaphase, translocates to the central spindle region and to the midbody during cytokinesis. Found in the sperm annulus. Colocalized with SPAG4 at the nuclear periphery in round spermatids, at sperm neck in elongated spermatids and at midpiece regions in ejaculated spermatozoa. Widely expressed. Expressed in lymph node. At the first step of spermiogenesis concentrated around the acrosome. Afterwards expressed between the edge of the acrosome and the perinuclear mantle of the manchette. Next, encircles the upper site of the acrosome and forms the rim of the sperm nucleus. With the formation of mitochondria and mature spermatozoa, localized at the neck and annulus regions. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.