Fast turnover of L1 adhesions in neuronal growth cones involving both surface diffusion and exo/endocytosis of L1 molecules

作者：Dequidt Caroline; Danglot Lydia; Alberts Philipp; Galli Thierry; Choquet Daniel; Thoumine Olivier^*

来源：Molecular Biology of the Cell, 2007, 18(8): 3131-3143.

DOI：10.1091/mbc.E06-12-1101

We investigated the interplay between surface trafficking and binding dynamics of the immunoglobulin cell adhesion molecule Ll at neuronal growth cones. Primary neurons were transfected with Ll constructs bearing thrombin-cleavable green fluorescent protein (GFP), allowing visualization of newly exocytosed Ll or labeling of membrane Ll molecules by Quantum dots. Intracellular L1-GFP vesicles showed preferential centrifugal motion, whereas surface L1-GFP diffused randomly, revealing two pathways to address Ll to adhesive sites. We triggered Ll 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]ability 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 Ll 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 Ll adhesions.

• 出版日期2007-8