Superfluous Role of Mammalian Septins 3 and 5 in Neuronal Development and Synaptic Transmission

Abstract

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.

ACKNOWLEDGMENTS

C.W.T. was supported by a Doctoral Research Award from the Canadian Institutes of Health Research, the RESTRCOMP Trainee Award from the Hospital for Sick Children, and the Joe A. Connolly Memorial Award from the Faculty of Medicine at the University of Toronto (Toronto, ON, Canada). W.S.T. and L.Y.W. are the recipients of Canada Research Chairs and are supported by the Canadian Institutes of Health Research (FRN 13465 and FRN 143867, respectively). P.J.R. is supported by grants from the Australian National Health and Medical Research Council.

We thank Audrey Lam (The Hospital for Sick Children) for growing, electroporation, and selection of ES clones; Linda Wei (The Hospital for Sick Children) for aggregation and animal breeding during the generation of the Sept3 knockout; Nancy Simpson (The University Health Network, Toronto, ON, Canada) for help with animal husbandry; Robert Temkin at the Advanced Bioimaging Center (The Hospital for Sick Children) for assistance with electron microscopy; and Yanchun Wang (Toronto Centre for Phenogenomics) and Bonnie Welsh (The Hospital for Sick Children) for their assistance with perfusion-fixation of mouse brains. We also thank Mathew Estey, Xiao-Rong Peng, Carol Froese, and Laura Pritzker for technical assistance and critical reading of the manuscript; Sergio Grinstein for the use of the digital image acquisition system; and especially Doris L. Fortin and Richard H. Kramer for their support during the revision of the manuscript.