Differential control of the releasable vesicle pools by SNAP-25 splice variants and SNAP-23.
The SNARE complex, consisting of synaptobrevin, syntaxin, and SNAP-25, is essential for calcium-triggered exocytosis in neurosecretory cells. Little is known, however, about how developmentally regulated isoforms and other cognate SNARE components regulate vesicular fusion. To address this question, we examined neuroexocytosis from chromaffin cells of Snap25 null mice rescued by the two splice variants SNAP-25a and SNAP-25b and the ubiquitously expressed homolog SNAP-23. In the absence of SNAP-25, vesicle docking persisted, but primed vesicle pools were empty and fast calcium-triggered release abolished. Single vesicular fusion events showed normal characteristics, except for a shorter duration of the fusion pore. Overexpression of SNAP-25a, SNAP-25b, and SNAP-23 resulted in three distinct phenotypes; SNAP-25b induced larger primed vesicle pools than SNAP-25a, whereas SNAP-23 did not support a standing pool of primed vesicles. We conclude that three alternative SNARE components support exocytosis, but they differ in their ability to stabilize vesicles in the primed state.
Sørensen
Jakob B
JB
Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. jsoeren@gwdg.de
Nagy
Gábor
G
Varoqueaux
Frederique
F
Nehring
Ralf B
RB
Brose
Nils
N
Wilson
Michael C
MC
Neher
Erwin
E
D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D019439:Chromaffin Cells / Q000378:metabolism* / Q000648:ultrastructure; D005089:Exocytosis / Q000235:genetics*; D005333:Fetus; D008561:Membrane Fusion / Q000235:genetics; D008565:Membrane Proteins / Q000172:deficiency* / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000235:genetics; D009489:Neurosecretion / Q000235:genetics*; D009490:Neurosecretory Systems / Q000378:metabolism* / Q000648:ultrastructure; D010641:Phenotype; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D022142:Secretory Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D050825:Synaptosomal-Associated Protein 25
D002352:Carrier Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human; C107017:Snap23 protein, mouse; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D002118:Calcium