Filament-forming cytoskeletal GTPase (Probable). Pro-apoptotic protein involved in LGR5-positive intestinal stem cell and Paneth cell expansion in the intestines, via its interaction with XIAP (By similarity). May also play a role in the regulation of cell fate in the intestine (By similarity). Positive regulator of apoptosis involved in hematopoietic stem cell homeostasis; via its interaction with XIAP (By similarity). Negative regulator of repair and hair follicle regeneration in response to injury, due to inhibition of hair follicle stem cell proliferation, potentially via its interaction with XIAP (By similarity). Plays an important role in male fertility and sperm motility (By similarity). During spermiogenesis, essential for the establishment of the annulus (a fibrous ring structure connecting the midpiece and the principal piece of the sperm flagellum) which is a requisite for the structural and mechanical integrity of the sperm (By similarity). Involved in the migration of cortical neurons and the formation of neuron leading processes during embryonic development (By similarity). Required for dopaminergic metabolism in presynaptic autoreceptors; potentially via activity as a presynaptic scaffold protein (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 SEPTIN8 (By similarity). 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 (By similarity). Interacts with SEPTIN14 (via C-terminus) (By similarity). Interacts with DYRK1A (By similarity). Interacts with SLC6A3/DAT and SNCA/alpha-synuclein (By similarity). Interacts with STX1A; in the striatum (By similarity). Interacts with XIAP (via BIR3 domain) following the induction of apoptosis (By similarity). Interacts with AREL1 (via HECT domain); in the cytoplasm following induction of apoptosis (By similarity). In platelets, found in areas surrounding alpha-granules (By similarity). Found in the sperm annulus, a fibrous ring structure connecting the midpiece and the principal piece of the sperm flagellum (By similarity). Expressed and colocalized with SLC6A3 and SNCA in axon terminals, especially at the varicosities (By similarity). Ubiquitinated by AREL1. Phosphorylated by DYRK1A. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.