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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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Quantitative evaluation of gold particle distribution at active zones at rest and during synaptic activity. The bar graph shows the ratio of gold particle densities between 0–100 nm and 100–200 nm from the active zone. At rest, n = 8; 5 Hz, n = 13, and K+ stimulation, n = 12.
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fig3: Quantitative evaluation of gold particle distribution at active zones at rest and during synaptic activity. The bar graph shows the ratio of gold particle densities between 0–100 nm and 100–200 nm from the active zone. At rest, n = 8; 5 Hz, n = 13, and K+ stimulation, n = 12.

Mentions: To examine the distribution of synapsin immunoreactivity at various stages of the synaptic vesicle cycle at the ultrastructural level, we stained reticulospinal synapses with synapsin antibodies at rest and during stimulation. Under resting conditions, synapsin was present predominantly on clustered vesicles located at a distance >100 nm from the presynaptic active zone (Fig. 2, B and C; Pieribone et al., 1995). In synapses stimulated at 5 Hz or exposed to elevated potassium Ringer's solution for 15 min, the distribution of synapsin immunolabeling in the 100-nm zone of the vesicle cluster immediately adjacent to the presynaptic membrane increased twofold (Fig. 2, D and E; Fig. 3; P < 0.01, unpaired t test). An even distribution of gold particles was observed in the distal portion of the cluster. By contrast, labeling of an integral vesicle membrane protein (synaptic vesicle protein 2 [SV2]) was uniformly distributed throughout the cluster at rest (Fig. 2 F; Fig. 3; P > 0.05, n = 16, unpaired t test). These data indicate that synapsin redistributes within the cluster during synaptic activity.


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)

Quantitative evaluation of gold particle distribution at active zones at rest and during synaptic activity. The bar graph shows the ratio of gold particle densities between 0–100 nm and 100–200 nm from the active zone. At rest, n = 8; 5 Hz, n = 13, and K+ stimulation, n = 12.
© Copyright Policy
Related In: Results  -  Collection

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

fig3: Quantitative evaluation of gold particle distribution at active zones at rest and during synaptic activity. The bar graph shows the ratio of gold particle densities between 0–100 nm and 100–200 nm from the active zone. At rest, n = 8; 5 Hz, n = 13, and K+ stimulation, n = 12.
Mentions: To examine the distribution of synapsin immunoreactivity at various stages of the synaptic vesicle cycle at the ultrastructural level, we stained reticulospinal synapses with synapsin antibodies at rest and during stimulation. Under resting conditions, synapsin was present predominantly on clustered vesicles located at a distance >100 nm from the presynaptic active zone (Fig. 2, B and C; Pieribone et al., 1995). In synapses stimulated at 5 Hz or exposed to elevated potassium Ringer's solution for 15 min, the distribution of synapsin immunolabeling in the 100-nm zone of the vesicle cluster immediately adjacent to the presynaptic membrane increased twofold (Fig. 2, D and E; Fig. 3; P < 0.01, unpaired t test). An even distribution of gold particles was observed in the distal portion of the cluster. By contrast, labeling of an integral vesicle membrane protein (synaptic vesicle protein 2 [SV2]) was uniformly distributed throughout the cluster at rest (Fig. 2 F; Fig. 3; P > 0.05, n = 16, unpaired t test). These data indicate that synapsin redistributes within the cluster during synaptic activity.

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