title: Assembly of presynaptic active zones from cytoplasmic transport packets.
abstract: Little is known about presynaptic assembly during central nervous system synaptogenesis. Here we used time-lapse fluorescence imaging, immunocytochemistry and electron microscopy to study hippocampal neuronal cultures transfected with a fusion construct of the presynaptic vesicle protein VAMP and green fluorescent protein. Our results suggest that major cytoplasmic and membrane-associated protein precursors of the presynaptic active zone are transported along developing axons together as discrete packets. Retrospective electron microscopy demonstrated varied vesicular and tubulovesicular membrane structures. Packets containing these heterogeneous structures were stabilized specifically at new sites of dendrite- and axon-initiated cell-cell contact; within less than one hour, evoked vesicle recycling was observed at these putative nascent synapses. These observations suggest that substantial membrane remodeling may be necessary to produce the uniform vesicles typical of the mature active zone, and that many presynaptic proteins may be united early in their biogenesis and sorting pathways.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Ahmari
authors.forename: J
authors.initials: J
authors.lastname: Buchanan
authors.forename: S J
authors.initials: SJ
authors.lastname: Smith
mesh_terms: D000818:Animals; D001370:Axonal Transport; D002450:Cell Communication; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D020439:Growth Cones / Q000378:metabolism / Q000648:ultrastructure; D006624:Hippocampus / Q000166:cytology / Q000196:embryology; D007150:Immunohistochemistry; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure*; D011498:Protein Precursors / Q000378:metabolism; D050683:R-SNARE Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure*; D014162:Transfection
chemical_list: D008565:Membrane Proteins; D011498:Protein Precursors; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins