Septins are cytoskeletal proteins conserved from algae and protists to mammals. A unique feature of septins is their presence as heteromeric complexes that polymerize into filaments in solution and on lipid membranes. Although animal septins associate extensively with actin-based structures in cells, whether septins organize as filaments in cells and if septin organization impacts septin function is not known. Customizing a tripartite split-GFP complementation assay, we show that all septins decorating actin stress fibers are octamer-containing filaments. Depleting octamers or preventing septins from polymerizing leads to a loss of stress fibers and reduced cell stiffness. Super-resolution microscopy revealed septin fibers with widths compatible with their organization as paired septin filaments. Nanometer-resolved distance measurements and single-protein tracking further showed that septin filaments are membrane bound and largely immobilized. Finally, reconstitution assays showed that septin filaments mediate actin–membrane anchoring. We propose that septin organization as octamer-based filaments is essential for septin function in anchoring and stabilizing actin filaments at the plasma membrane.
Human septins organize as octamer-based filaments and mediate actin-membrane anchoring in cells
Disclosures: The authors declare no competing interests exist.
P. Verdier-Pinard's and A. Badache’s current affiliation is Aix Marseille Univ, INSERM, MMG, U1251, Marseille, France.
- Award Id(s): ANR-17-CE13-0014,ANR-17-CE09-0026-01,ANR-20-CE42-0003
- Award Id(s): ARCDOC42020010001242
- Award Id(s): ANR-10-INBS-04
- Award Id(s): 723241,772257,812772
- Award Id(s): R01GM122375,1S10RR026866-01,1S10OD018136-01
- Award Id(s): 024.003.019
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Carla Silva Martins, Cyntia Taveneau, Gerard Castro-Linares, Mikhail Baibakov, Nicolas Buzhinsky, Mar Eroles, Violeta Milanović, Shizue Omi, Jean-Denis Pedelacq, Francois Iv, Léa Bouillard, Alexander Llewellyn, Maxime Gomes, Mayssa Belhabib, Mira Kuzmić, Pascal Verdier-Pinard, Stacey Lee, Ali Badache, Sanjay Kumar, Cristel Chandre, Sophie Brasselet, Felix Rico, Olivier Rossier, Gijsje H. Koenderink, Jerome Wenger, Stéphanie Cabantous, Manos Mavrakis; Human septins organize as octamer-based filaments and mediate actin-membrane anchoring in cells. J Cell Biol 6 March 2023; 222 (3): e202203016. doi: https://doi.org/10.1083/jcb.202203016
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