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Colocalization of synapsin and actin during synaptic vesicle recycling.

Bloom O, Evergren E, Tomilin N, Kjaerulff O, Löw P, Brodin L, Pieribone VA, Greengard P, Shupliakov O - J. Cell Biol. (2003)

Bottom Line: In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones.Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster.Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses.

View Article: PubMed Central - PubMed

Affiliation: The Rockefeller University, New York, NY 10021, USA. ona@chronos.med.yale.edu

ABSTRACT
It has been hypothesized that in the mature nerve terminal, interactions between synapsin and actin regulate the clustering of synaptic vesicles and the availability of vesicles for release during synaptic activity. Here, we have used immunogold electron microscopy to examine the subcellular localization of actin and synapsin in the giant synapse in lamprey at different states of synaptic activity. In agreement with earlier observations, in synapses at rest, synapsin immunoreactivity was preferentially localized to a portion of the vesicle cluster distal to the active zone. During synaptic activity, however, synapsin was detected in the pool of vesicles proximal to the active zone. In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones. Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster. Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses. Our data suggest that in addition to its known function in clustering of vesicles in the reserve pool, synapsin migrates from the synaptic vesicle cluster and participates in the organization of the actin-rich cytomatrix in the endocytic zone during synaptic activity.

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Localization of synapsin in the endocytic zone. Electron micrographs from synapses double labeled with synapsin (small particles) and SV2 (large particles) antibodies. Note an even distribution of both antigens in the vesicle cluster in A and the accumulation of only SV2 immunoreactivity on the plasma membrane and endocytic intermediates in B and C. Bar, 100 nm.
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fig6: Localization of synapsin in the endocytic zone. Electron micrographs from synapses double labeled with synapsin (small particles) and SV2 (large particles) antibodies. Note an even distribution of both antigens in the vesicle cluster in A and the accumulation of only SV2 immunoreactivity on the plasma membrane and endocytic intermediates in B and C. Bar, 100 nm.

Mentions: To address the possible pathway by which synapsin becomes associated with the actin cytomatrix and recycling vesicles, we investigated if synapsin labeling is associated with clathrin-coated intermediates. Both action potential–stimulated (5 Hz) and K+-stimulated synapses were examined. In neither case did we detect labeling of coated intermediates or of the plasma membrane. This was particularly evident in preparations stimulated with high K+, in which numerous endocytic intermediates occurred at the endocytic zone (Fig. 5, E and F; see also Fig. 2 G). Ultrathin sections were stained with both synapsin and SV2 antibodies (Fig. 6, A–C). As in previous experiments, SV2 antibodies efficiently labeled synaptic vesicle clusters (Fig. 6 A). In addition, SV2 immunolabeling was observed on coated intermediates as well as on the plasma membrane in the endocytic zone (Fig. 6, B and C). These results indicate that synapsin is not linked to the vesicle membrane before endocytosis, but associates with the recycled vesicle after it has been released into the cytoplasm.


Colocalization of synapsin and actin during synaptic vesicle recycling.

Bloom O, Evergren E, Tomilin N, Kjaerulff O, Löw P, Brodin L, Pieribone VA, Greengard P, Shupliakov O - J. Cell Biol. (2003)

Localization of synapsin in the endocytic zone. Electron micrographs from synapses double labeled with synapsin (small particles) and SV2 (large particles) antibodies. Note an even distribution of both antigens in the vesicle cluster in A and the accumulation of only SV2 immunoreactivity on the plasma membrane and endocytic intermediates in B and C. Bar, 100 nm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199372&req=5

fig6: Localization of synapsin in the endocytic zone. Electron micrographs from synapses double labeled with synapsin (small particles) and SV2 (large particles) antibodies. Note an even distribution of both antigens in the vesicle cluster in A and the accumulation of only SV2 immunoreactivity on the plasma membrane and endocytic intermediates in B and C. Bar, 100 nm.
Mentions: To address the possible pathway by which synapsin becomes associated with the actin cytomatrix and recycling vesicles, we investigated if synapsin labeling is associated with clathrin-coated intermediates. Both action potential–stimulated (5 Hz) and K+-stimulated synapses were examined. In neither case did we detect labeling of coated intermediates or of the plasma membrane. This was particularly evident in preparations stimulated with high K+, in which numerous endocytic intermediates occurred at the endocytic zone (Fig. 5, E and F; see also Fig. 2 G). Ultrathin sections were stained with both synapsin and SV2 antibodies (Fig. 6, A–C). As in previous experiments, SV2 antibodies efficiently labeled synaptic vesicle clusters (Fig. 6 A). In addition, SV2 immunolabeling was observed on coated intermediates as well as on the plasma membrane in the endocytic zone (Fig. 6, B and C). These results indicate that synapsin is not linked to the vesicle membrane before endocytosis, but associates with the recycled vesicle after it has been released into the cytoplasm.

Bottom Line: In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones.Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster.Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses.

View Article: PubMed Central - PubMed

Affiliation: The Rockefeller University, New York, NY 10021, USA. ona@chronos.med.yale.edu

ABSTRACT
It has been hypothesized that in the mature nerve terminal, interactions between synapsin and actin regulate the clustering of synaptic vesicles and the availability of vesicles for release during synaptic activity. Here, we have used immunogold electron microscopy to examine the subcellular localization of actin and synapsin in the giant synapse in lamprey at different states of synaptic activity. In agreement with earlier observations, in synapses at rest, synapsin immunoreactivity was preferentially localized to a portion of the vesicle cluster distal to the active zone. During synaptic activity, however, synapsin was detected in the pool of vesicles proximal to the active zone. In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones. Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster. Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses. Our data suggest that in addition to its known function in clustering of vesicles in the reserve pool, synapsin migrates from the synaptic vesicle cluster and participates in the organization of the actin-rich cytomatrix in the endocytic zone during synaptic activity.

Show MeSH
Related in: MedlinePlus