ABSTRACT
Axons and dendrites are long and often ramified neurites that need particularly intense plasma membrane (PM) expansion during the development of the nervous system. Neurite growth depends on non-fusogenic Sec22b–Stx1 SNARE complexes at endoplasmic reticulum (ER)–PM contacts. Here, we show that Sec22b interacts with members of the extended synaptotagmin (E-Syt) family of ER lipid transfer proteins (LTPs), and this interaction depends on the longin domain of Sec22b. Overexpression of E-Syts stabilizes Sec22b–Stx1 association, whereas silencing of E-Syts has the opposite effect. Overexpression of wild-type E-Syt2, but not mutants unable to transfer lipids or attach to the ER, increase the formation of axonal filopodia and ramification of neurites in developing neurons. This effect is inhibited by a clostridial neurotoxin cleaving Stx1, and expression of the Sec22b longin domain and a Sec22b mutant with an extended linker between the SNARE and transmembrane domains. We conclude that Sec22b–Stx1 ER–PM contact sites contribute to PM expansion by interacting with LTPs, such as E-Syts.
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Footnotes
Author contributions
Conceptualization: C.V., T.G.; Methodology: A.G., L.D., F.G., T.B., C.V.; Software: L.D.; Validation: T.G.; Formal analysis: F.G., B.H.; Investigation: A.G., L.D., F.G., B.H., C.V.; Data curation: A.G.; Writing - original draft: A.G., L.D., C.V., T.G.; Writing - review & editing: A.G., T.G.; Supervision: T.G.; Project administration: T.G.; Funding acquisition: T.G.
Funding
This work was funded by grants from the Association Française contre les Myopathies (Research Grant 16612), the French National Research Agency (Agence Nationale de la Recherche; NeuroImmunoSynapse ANR-13-BSV2-0018-02; MetDePaDi ANR-16-CE16-0012), the Institut National du Cancer (PLBIO 2018-149), the Fondation pour la Recherche Médicale (FRM), Who am I? Labex (Idex ANR-11-IDEX-0005-01), awards of the Association Robert Debré pour la Recherche Médicale and Fondation Bettencourt-Schueller, Idex USPC (‘Conventional And Unconventional Secretion In Neurite Growth’) to T.G.
