Assembly of synapses by neuronal adhesion molecules: single molecule studies

Transcription

1 Assembly of synapses by neuronal adhesion molecules: single molecule studies Olivier Thoumine Interdisciplinary Institute of Neurosciences CNRS - University of Bordeaux

2 Connectivity in the brain 300 nm Micheva et al. Neuron 2010

3 Molecular determinants of synapse formation Ziv and Garner Current Opinion in Neurobiology 2001

4 Experimental approach Spontaneous contacts Low spatial and temporal resolution Coexistence of multiple molecules Unknown stoichiometry Biomimetic contacts Use purified proteins Control surface density Control position and time of contact

5 Biomimetic assays Purified Neurexin1 Fc Quantum dots (20 nm) kd Microspheres (1 µm) Micro-patterns (2 µm) Primary hippocampal neurons

6 Outline 1. Growth cone migration 2. Post-synaptic morphing 3. Synapse formation

7 Axis 1: Growth cone motility Central domain - + Filopodia Lamellipodium F-actin Microtubules Myosin II Actin flow 0.2 µm

8 The molecular clutch mechanism: focus on N-cadherin Myosin Actin flow Clutch Membrane protrusion 1. Binding Cadherins Adhesion 2. Coupling p120 Membrane -catenin -catenin Vinculin F-actin 3. Force Myosin Boggon et al. Science 2002 Giannone, Mège, Thoumine Trends Cell Biol 2009

9 Bead displacement (µm) N-cadherin based molecular clutch in the growth cone Optical trap 2,5 Ncad-Fc 2 1 µg/cm 2 Escape 1,5 Actin flow N-cadherin 1 0,5 0 Ncad-Fc 0.1 µg/cm 2 Breaking events Bard, et al. J. Neurosci , Time (sec) Fc 1 µg/cm 2

10 Mapping the actin flow in growth cones Cell PEG Glass N-cadherin Anti-Fc TIRF 5 µm Garcia et al., unpublished

11 Korobova & Svitkina Mol Biol Cell 2010 Axis 2: Dendritic spine morphing

12 Rationale Axon Filopodium Spine Dendrite N-cadherin Catenins F-actin Protrusion F-actin flow Myosin II Microtubules

13 Subspine localization and dynamics N-cadherin-GFP Myosin-GFP RFP F-actin Actin retraction upon myosin stimulation 1 µm 0 min 10 min Chazeau et al., in preparation

14 Optical tweezers experiments <0 min 0 min 2 min 1 µm 0 min 10 min Actin-GFP Bead N-cadherin

15 Axis 3: Synapse differentiation via neurexin/neuroligin adhesion CASK Vesicle Neurexin-1 Binding Neuroligin-1 Glutamate AMPA receptor Sudhof, Nature 2008 Craig & Kang, Curr Opin Neurobiol 2007 PSD-95 Signaling Fonction

16 Detachment of neurexin-coated Quantum dots Quantum dot Neurexin-1 Neuroligin-1 Cell k on k off GFP Cell membrane Individual detachment event 2 µm Saint-Michel et al., Biophys J 2009

17 Fraction of attached QD A sensitive method to probe protein interactions 1,2 1 0,8 0,6 0,4 Anti-HA Nrx1β-Fc Nrx1β-Fc + soluble Nrx1β-Fc 0,2 0 Nrx1β-Fc + EGTA Time (min) 5 µm 2 µm

18 Assembly of functional post-synapses Iontophoretic pipette DIC PSD95-mCherry Synaptotagmin Patch pipette 2 µm bead Pipet Neurite Synapse Neurexin Glutamate bead Neuroligin PSD-95 AMPAR 50 pa 50 ms Heine et al. PNAS 2008

19 AMPA receptor diffusion (µm²/s) Neuroligin-1 expression decreases AMPAR lateral diffusion Quantum dot Neuroligin-1 Control + Neuroligin-1 AMPA receptor 0.4 5µm GluA2 *** *** GluA ns Nlg1 WT

20 Nlg1 KO Nlg1 WT AMPA receptor diffusion (µm²/s) +Nlg1 +shnlg1 Neuroligin-1 bi-directionally modulates AMPAR lateral diffusion +shnlg1 & GFP 0.15 *** *** *** 4 µm Nlg1 WT 0.00 Nlg1 WT Nlg1 KO Mondin et al., J. Neurosci, 2011

21 Summary Synapse AMPA receptor Neurexin-1 Neuroligin-1 PSD-95 Diffusion Trapping Competition

22 Model parameters Model Trapping Membrane Diffusion k on k off Endo/exocytosis AMPA receptor PSD Simulation 1 µm Czöndör et al. PNAS 2012

23 Ashby et al., J Neurosci 2006 Frischknecht et al., Nat Neurosci 2009 Predicting FRAP experiments

24 AMPAR enrichment at synapses Projection Synapse size PSD= 0.1 µm 0.2 µm 0.4 µm Tanaka et al., J Neurosci 2005

25 Synaptic AMPAR exocytosis Synaptic exocytosis+ High trapping High trapping Synaptic exocytosis Kennedy et al., Cell 2010; Patterson et al. PNAS 2011

26 Introducing AMPAR endocytosis Extra-synaptic endocytosis Low trapping Synaptic endocytosis Low trapping + Synaptic endocytosis Racz et al., Nat Neurosci 2004

27 Conclusions A sequential scenario: 1. Growth cones migrate to find their targets 2. Synapses are assembled 3. Synapses undergo morphological and functional plasticity

28 Acknowledgments Biophysics of Adhesion & Cytoskeleton M. Mondin K. Czöndör M. Garcia A. Chazeau F. Néca B. Tessier O. Rossier G. Giannone Reagents CYTOO SA A. Fuchs A. Argento Collaborators M. Heine R. Frischknecht J.B.Sibarita E. Hosy D. Choquet V. Labrousse C. Mulle P. Scheiffele N. Brose F. Varoqueaux O. Schlüter M.Ehlers R.M.-Mège Bordeaux Imaging Center C. Poujol P. Legros F. Levet S. Marais Animal care A. Vimeney A. Lacquement N. Grosjean Cell culture C. Breillat D. Bouchet A. Frouin R. Sterling Funding