Filament-forming cytoskeletal GTPase. May play a role in cytokinesis (Potential). May play a role in the cytoarchitecture of neurons, including dendritic arborization and dendritic spines, and in GABAergic synaptic connectivity. Septins polymerize into heterooligomeric protein complexes that form filaments, and can associate with cellular membranes, actin filaments and microtubules (By similarity). Forms homooligomers (By similarity). GTPase activity is required for filament formation (By similarity). Interacts with SEPTIN7 (PubMed:15485874). Interacts with SEPTIN9 and SEPTIN12 (By similarity). Partly colocalizes with stress fibers. Association with microtubules not observed in embryonic fibroblasts. In cultured hippocampal neurons, localizes to 54% of GABAergic and 25% of glutamatergic synapses. Frequently present at the base of dendritic protrusions and at the bifurcation points of the dendritic branches. Expressed at low levels in the axons of mature cultured hippocampal neurons. In embryonic fibroblasts, associated with actin stress fibers. Highly expressed in cerebellum, olfactory bulb, hippocampus, cerebral cortex, thalamus, and corpus striatum. In the hippocampus, strong expression around the pyramidal cells of the stratum pyramidale and in the stratum lucidum of the CA2-CA3 regions. In the olfactory bulb, particularly strong expression in the external plexiform layer. In the cerebellum, concentrates in the molecular layer, particularly in Purkinje cells, where it is found at the base of dendritic spines/protrusions, at the dendritic branching points and in some GABAergic synapses. Expressed in the embryo and in early postnatal weeks. On and before P14, distributes in a homogeneous way, throughout the brain. By P21, high expression observed in the molecular layer of the cerebellum and in the olfactory bulb. The maximum expression and the adult pattern of distribution in the brain occurs by P30. By P30, P45 and P90, highest expression occurs in the molecular layer of the cerebellum and in the olfactory bulb, and relatively high expression in the hippocampus, cerebral cortex, thalamus and corpus striatum. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.