Superfluous role of mammalian septins 3 and 5 in neuronal development and synaptic transmission.

The septin family of GTPases, first identified for their roles in cell division, are also expressed in postmitotic tissues. SEPT3 (G-septin) and SEPT5 (CDCrel-1) are highly expressed in neurons, enriched in presynaptic terminals, and associated with synaptic vesicles. These characteristics suggest that SEPT3 or SEPT5 might be important for synapse formation, maturation, or synaptic vesicle traffic. Since Sept5(-/-) mice do not show any overt neurological phenotypes, we generated Sept3(-/-) and Sept3(-/-) Sept5(-/-) mice and found that SEPT3 and SEPT5 are not essential for development, fertility, or viability. Changes in the expression of septins were noted in the absence of SEPT3, SEPT5, and both septins. SEPT5 association with other septins in brain tissue was unaffected by the removal of SEPT3. No abnormalities were observed in the gross morphology and synapses of the hippocampus. Similarly, axon development and synapse formation were unaffected in vitro. In cultured hippocampal neurons, the size of the recycling synaptic vesicle pool was unaltered in the absence of SEPT3. Furthermore, synaptic transmission at two different central synapses was not significantly affected in Sept3(-/-) Sept5(-/-) mice. These results indicate that SEPT3 and SEPT5 are dispensable for neuronal development as well as for synaptic vesicle fusion and recycling.