Three-dimensional architecture of presynaptic terminal cytomatrix.
Presynaptic terminals are specialized for mediating rapid fusion of synaptic vesicles (SVs) after calcium influx. The regulated trafficking of SVs likely results from a highly organized cytomatrix. How this cytomatrix links SVs, maintains them near the active zones (AZs) of release, and organizes docked SVs at the release sites is not fully understood. To analyze the three-dimensional (3D) architecture of the presynaptic cytomatrix, electron tomography of presynaptic terminals contacting spines was performed in the stratum radiatum of the rat hippocampal CA1 area. To preserve the cytomatrix, hippocampal slices were immobilized using high-pressure freezing, followed by cryosubstitution and embedding. SVs are surrounded by a dense network of filaments. A given vesicle is connected to approximately 1.5 neighboring ones. SVs at the periphery of this network are also linked to the plasma membrane, by longer filaments. More of these filaments are found at the AZ. At the AZ, docked SVs are grouped around presynaptic densities. Filaments with adjacent SVs emerge from these densities. Immunogold localizations revealed that synapsin is located in the presynaptic bouton, whereas Bassoon and CAST (ERC2) are at focal points next to the AZ. In synapsin triple knock-out mice, the number of SVs is reduced by 63%, but the size of the boutons is reduced by only 18%, and the mean distance of SVs to the AZ is unchanged. This 3D analysis reveals the morphological constraints exerted by the presynaptic molecular scaffold. SVs are tightly interconnected in the axonal bouton, and this network is preferentially connected to the AZ.
Siksou
Léa
L
Inserm U789, Ecole Normale Supérieure, 75005 Paris, France.
Rostaing
Philippe
P
Lechaire
Jean-Pierre
JP
Boudier
Thomas
T
Ohtsuka
Toshihisa
T
Fejtová
Anna
A
Kao
Hung-Teh
HT
Greengard
Paul
P
Gundelfinger
Eckart D
ED
Triller
Antoine
A
Marty
Serge
S
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D049229:Dendritic Spines / Q000378:metabolism / Q000648:ultrastructure*; D005109:Extracellular Matrix / Q000378:metabolism / Q000648:ultrastructure*; D006624:Hippocampus / Q000378:metabolism / Q000648:ultrastructure*; D019044:Image Cytometry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009924:Organ Culture Techniques; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016704:Synapsins / Q000235:genetics / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D014057:Tomography, X-Ray Computed
D048868:Adaptor Proteins, Signal Transducing; C113688:Bsn protein, rat; C479909:ERC1 protein, rat; D009419:Nerve Tissue Proteins; D016704:Synapsins