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Differential roles for snapin and synaptotagmin in the synaptic vesicle cycle.

Yu SC, Klosterman SM, Martin AA, Gracheva EO, Richmond JE - PLoS ONE (2013)

Bottom Line: The kinetics of synaptic transmission were unaffected at snpn-1 mutant neuromuscular junctions (NMJs), but the number of docked, fusion competent vesicles was significantly reduced.However, analyses of snt-1 and snt-1;snpn-1 double mutants suggest that the docking role of SNPN-1 is independent of Synaptotagmin.Based on these results we propose that the primary role of Snapin in C. elegans is to promote vesicle priming, consistent with the stabilization of SNARE complex formation through established interactions with SNAP-25 upstream of the actions of Synaptotagmin in calcium-sensing and endocytosis.

View Article: PubMed Central - PubMed

Affiliation: Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America.

ABSTRACT
Evoked synaptic transmission is dependent on interactions between the calcium sensor Synaptotagmin I and the SNARE complex, comprised of Syntaxin, SNAP-25, and Synaptobrevin. Recent evidence suggests that Snapin may be an important intermediate in this process, through simultaneous interactions of Snapin dimers with SNAP-25 and Synaptotagmin. In support of this model, cultured neurons derived from embryonically lethal Snapin mutant mice exhibit desynchronized release and a reduced readily releasable vesicle pool. Based on evidence that a dimerization-defective Snapin mutation specifically disrupts priming, Snapin is hypothesized to stabilize primed vesicles by structurally coupling Synaptotagmin and SNAP-25. To explore this model in vivo we examined synaptic transmission in viable, adult C. elegans Snapin (snpn-1) mutants. The kinetics of synaptic transmission were unaffected at snpn-1 mutant neuromuscular junctions (NMJs), but the number of docked, fusion competent vesicles was significantly reduced. However, analyses of snt-1 and snt-1;snpn-1 double mutants suggest that the docking role of SNPN-1 is independent of Synaptotagmin. Based on these results we propose that the primary role of Snapin in C. elegans is to promote vesicle priming, consistent with the stabilization of SNARE complex formation through established interactions with SNAP-25 upstream of the actions of Synaptotagmin in calcium-sensing and endocytosis.

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The functional defects of snpn-1 and snt-1 mutants are not associated with reduced synaptic density.(A) Representative confocal images of dorsal cord synaptic puncta visualized using the GFP tagged synaptic vesicle protein, Synaptobrevin (SNB-1::GFP). (B–C) Quantification of the mean ± SEM synaptic vesicle density and SNB-1::GFP puncta fluorescence show no significant differences between the snpn-1 and snt-1 mutants relative to wild-type.
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pone-0057842-g003: The functional defects of snpn-1 and snt-1 mutants are not associated with reduced synaptic density.(A) Representative confocal images of dorsal cord synaptic puncta visualized using the GFP tagged synaptic vesicle protein, Synaptobrevin (SNB-1::GFP). (B–C) Quantification of the mean ± SEM synaptic vesicle density and SNB-1::GFP puncta fluorescence show no significant differences between the snpn-1 and snt-1 mutants relative to wild-type.

Mentions: Cultured hippocampal neurons from Snapin mutant mice have significantly fewer synapses [15]. If this phenotype is conserved, it could explain the behavioral and electrophysiological defects observed in C. elegans snpn-1 mutants. To test whether snpn-1 mutants have altered synaptic density, we crossed a transgenic line expressing GFP-tagged Synaptobrevin under the cholinergic neuronal promoter Pacr-2 into the snpn-1 mutant background. GFP puncta along the dorsal nerve cord, where individual cholinergic synapses can be readily discerned, were imaged and scored to provide a measure of synaptic density (Fig. 3). Neither the density (p = 0.51) nor average fluorescence intensity (p = 0.061) of puncta was altered in snpn-1 mutants when compared to the wild type, indicating that the observed locomotory and electrophysiological defects were not the result of altered synaptic number (Fig. 3B,C). Similarly, snt-1 mutants showed normal synaptic density (p = 0.57) and puncta intensity (p = 0.22) (Fig. 3B,C).


Differential roles for snapin and synaptotagmin in the synaptic vesicle cycle.

Yu SC, Klosterman SM, Martin AA, Gracheva EO, Richmond JE - PLoS ONE (2013)

The functional defects of snpn-1 and snt-1 mutants are not associated with reduced synaptic density.(A) Representative confocal images of dorsal cord synaptic puncta visualized using the GFP tagged synaptic vesicle protein, Synaptobrevin (SNB-1::GFP). (B–C) Quantification of the mean ± SEM synaptic vesicle density and SNB-1::GFP puncta fluorescence show no significant differences between the snpn-1 and snt-1 mutants relative to wild-type.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585204&req=5

pone-0057842-g003: The functional defects of snpn-1 and snt-1 mutants are not associated with reduced synaptic density.(A) Representative confocal images of dorsal cord synaptic puncta visualized using the GFP tagged synaptic vesicle protein, Synaptobrevin (SNB-1::GFP). (B–C) Quantification of the mean ± SEM synaptic vesicle density and SNB-1::GFP puncta fluorescence show no significant differences between the snpn-1 and snt-1 mutants relative to wild-type.
Mentions: Cultured hippocampal neurons from Snapin mutant mice have significantly fewer synapses [15]. If this phenotype is conserved, it could explain the behavioral and electrophysiological defects observed in C. elegans snpn-1 mutants. To test whether snpn-1 mutants have altered synaptic density, we crossed a transgenic line expressing GFP-tagged Synaptobrevin under the cholinergic neuronal promoter Pacr-2 into the snpn-1 mutant background. GFP puncta along the dorsal nerve cord, where individual cholinergic synapses can be readily discerned, were imaged and scored to provide a measure of synaptic density (Fig. 3). Neither the density (p = 0.51) nor average fluorescence intensity (p = 0.061) of puncta was altered in snpn-1 mutants when compared to the wild type, indicating that the observed locomotory and electrophysiological defects were not the result of altered synaptic number (Fig. 3B,C). Similarly, snt-1 mutants showed normal synaptic density (p = 0.57) and puncta intensity (p = 0.22) (Fig. 3B,C).

Bottom Line: The kinetics of synaptic transmission were unaffected at snpn-1 mutant neuromuscular junctions (NMJs), but the number of docked, fusion competent vesicles was significantly reduced.However, analyses of snt-1 and snt-1;snpn-1 double mutants suggest that the docking role of SNPN-1 is independent of Synaptotagmin.Based on these results we propose that the primary role of Snapin in C. elegans is to promote vesicle priming, consistent with the stabilization of SNARE complex formation through established interactions with SNAP-25 upstream of the actions of Synaptotagmin in calcium-sensing and endocytosis.

View Article: PubMed Central - PubMed

Affiliation: Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America.

ABSTRACT
Evoked synaptic transmission is dependent on interactions between the calcium sensor Synaptotagmin I and the SNARE complex, comprised of Syntaxin, SNAP-25, and Synaptobrevin. Recent evidence suggests that Snapin may be an important intermediate in this process, through simultaneous interactions of Snapin dimers with SNAP-25 and Synaptotagmin. In support of this model, cultured neurons derived from embryonically lethal Snapin mutant mice exhibit desynchronized release and a reduced readily releasable vesicle pool. Based on evidence that a dimerization-defective Snapin mutation specifically disrupts priming, Snapin is hypothesized to stabilize primed vesicles by structurally coupling Synaptotagmin and SNAP-25. To explore this model in vivo we examined synaptic transmission in viable, adult C. elegans Snapin (snpn-1) mutants. The kinetics of synaptic transmission were unaffected at snpn-1 mutant neuromuscular junctions (NMJs), but the number of docked, fusion competent vesicles was significantly reduced. However, analyses of snt-1 and snt-1;snpn-1 double mutants suggest that the docking role of SNPN-1 is independent of Synaptotagmin. Based on these results we propose that the primary role of Snapin in C. elegans is to promote vesicle priming, consistent with the stabilization of SNARE complex formation through established interactions with SNAP-25 upstream of the actions of Synaptotagmin in calcium-sensing and endocytosis.

Show MeSH
Related in: MedlinePlus