Morphological and molecular heterogeneity in release sites of single neurons.
We have previously shown that labelling intensities for synaptic proteins vary strongly among synaptic boutons. Here we addressed the questions as to whether there are heterogeneous levels of integral membrane synaptic vesicle proteins at distinct active release sites of single neurons and if these sites possess the ultrastructural features of synapses. By double-immunostaining with specific antibodies against synaptophysin, synaptotagmin I, VAMP1 and VAMP2, we identified different relative levels of these integral membrane proteins of synaptic vesicles in comparison to boutons of the same rat cortical neuron. This heterogeneity could also be observed between the two isoforms VAMP1 and VAMP2. By studying pairs of these proteins implicated in neurotransmitter release, including both VAMP isoforms, we also show that the sites that contained predominantly one protein were nevertheless functional, as they internalized and released FM1-43 upon potassium stimulation. Using electron microscopy, we show that these active sites could have either synaptic specializations, or the features of vesicle-containing varicosities without a postsynaptic target. Different varicosities of the same neuron showed different intensities for synaptic vesicle proteins; some varicosities were capable of internalizing and releasing FM1-43, while others were silent. These results show that integral membrane synaptic vesicle proteins are differentially distributed among functional release sites of the same neuron.
Morgenthaler
Florence D
FD
Institut de Biologie Cellulaire et de Morphologie (IBCM), Rue du Bugnon 9, 1005 Lausanne, Switzerland. Florence.Morgenthaler@epfl.ch
Knott
Graham W
GW
Floyd Sarria
J-C
JC
Wang
Xin
X
Staple
Julie K
JK
Catsicas
Stefan
S
Hirling
Harald
H
D000818:Animals; D000831:Animals, Newborn; D002135:Calcium-Binding Proteins; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism; D058969:Contactin 2; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D050683:R-SNARE Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D013570:Synaptic Membranes / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism; D016708:Synaptophysin / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D050863:Synaptotagmin I; D050857:Synaptotagmins; D013997:Time Factors
D002135:Calcium-Binding Proteins; D015816:Cell Adhesion Molecules, Neuronal; C548676:Cntn2 protein, rat; D058969:Contactin 2; C073804:FM1 43; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D050683:R-SNARE Proteins; C079052:SVP-38 protein, rat; C494210:Snap25 protein, rat; D016708:Synaptophysin; D050825:Synaptosomal-Associated Protein 25; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; D050857:Synaptotagmins; D011188:Potassium