Filament-forming cytoskeletal GTPase (By similarity). Involved in the morphogenesis of sperm heads and the elongation of sperm tails probably implicating the association with alpha- and beta- tubulins (PubMed:24213608). Facilitates the formation of Septin filament structures with SEPTIN7, SEPTIN6, SEPTIN2 and SEPTIN4 at the sperm annulus (PubMed:25588830, PubMed:28346465). Correct formation of the annulus is required for development of normal structural morphology and motility of the sperm during steps 13 to 16 of spermiogenesis (PubMed:25588830). Essential component of the LMNB1/SUN5/SEPT12 bridge that connects the sperm proximal centriole to the implantation fossa, the bridge functions to prevent detachment of the proximal centriole from the posterior nucleus during steps 13 to 16 of spermiogenesis (PubMed:38870534). Required for PLCZ1 localization at the sperm acrosome during spermiogenesis (By similarity). May also play a role in the initiation of calcium oscillations in embryos (By similarity). {ECO:0000250|UniProtKB:A0A2R8VJU7, ECO:0000250|UniProtKB:Q9NVA2, ECO:0000269|PubMed:24213608, ECO:0000269|PubMed:25588830, ECO:0000269|PubMed:28346465, ECO:0000269|PubMed:38870534}. This is the function of SEPTIN12 (septin 12, Ensembl gene identifier ENSG00000140623).