Filament-forming cytoskeletal GTPase. Required for normal organization of the actin cytoskeleton. Required for normal progress through mitosis. Involved in cytokinesis (By similarity). Plays a role in ciliogenesis and collective cell movements including convergent extension during gastrulation. Controls cell elongation but not polarization during convergent extension. Monomer, and homodimer. Nucleotide binding promotes oligomerization. Can form heterooligomers with other family members and form filaments (By similarity). Expressed in the mesoderm during gastrulation. Expressed in the notochord of neurula stage embryos. Coordinated expression with septin2 and septin6. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.