title: Fast turnover of L1 adhesions in neuronal growth cones involving both surface diffusion and exo/endocytosis of L1 molecules.
abstract: We investigated the interplay between surface trafficking and binding dynamics of the immunoglobulin cell adhesion molecule L1 at neuronal growth cones. Primary neurons were transfected with L1 constructs bearing thrombin-cleavable green fluorescent protein (GFP), allowing visualization of newly exocytosed L1 or labeling of membrane L1 molecules by Quantum dots. Intracellular L1-GFP vesicles showed preferential centrifugal motion, whereas surface L1-GFP diffused randomly, revealing two pathways to address L1 to adhesive sites. We triggered L1 adhesions using microspheres coated with L1-Fc protein or anti-L1 antibodies, manipulated by optical tweezers. Microspheres coupled to the actin retrograde flow at the growth cone periphery while recruiting L1-GFP molecules, of which 50% relied on exocytosis. Fluorescence recovery after photobleaching experiments revealed a rapid recycling of L1-GFP molecules at L1-Fc (but not anti-L1) bead contacts, attributed to a high lability of L1-L1 bonds at equilibrium. L1-GFP molecules truncated in the intracellular tail as well as neuronal cell adhesion molecules (NrCAMs) missing the clathrin adaptor binding sequence showed both little internalization and reduced turnover rates, indicating a role of endocytosis in the recycling of mature L1 contacts at the base of the growth cone. Thus, unlike for other molecules such as NrCAM or N-cadherin, diffusion/trapping and exo/endocytosis events cooperate to allow the fast renewal of L1 adhesions.
authors.affiliation: Unité Mixte de Recherche Centre National de la Recherche Scientifique 5091, Institut François Magendie, Université Bordeaux 2, 33077 Bordeaux, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Dequidt
authors.forename: Lydia
authors.initials: L
authors.lastname: Danglot
authors.forename: Philipp
authors.initials: P
authors.lastname: Alberts
authors.forename: Thierry
authors.initials: T
authors.lastname: Galli
authors.forename: Daniel
authors.initials: D
authors.lastname: Choquet
authors.forename: Olivier
authors.initials: O
authors.lastname: Thoumine
mesh_terms: D000268:Adhesiveness; D000818:Animals; D019556:COS Cells; D016764:Cell Polarity; D002522:Chlorocebus aethiops; D004058:Diffusion; D004705:Endocytosis; D005089:Exocytosis; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D020439:Growth Cones / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008863:Microspheres; D008954:Models, Biological; D039842:Neural Cell Adhesion Molecule L1 / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D011961:Receptors, Fc / Q000378:metabolism; D013499:Surface Properties
chemical_list: D039842:Neural Cell Adhesion Molecule L1; D011961:Receptors, Fc; D049452:Green Fluorescent Proteins