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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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3-D distribution of synapsin in stimulated reticulospinal synapse. (A) Electron micrograph of one serial section of a reticulospinal synapse stimulated at 5 Hz for 20 min, shown reconstructed in B. Synapsin is present on vesicles (v) in the filamentous cytomatrix (arrow). svc, synaptic vesicle cluster; v, vesicles in the filamentous matrix; d, dendrite; a, axoplasmic matrix. ccp, clathrin-coated pit. This arrow indicates active zone. (B) 3-D reconstruction of 10 serial ultrathin sections. The area occupied by actin-rich filamentous cytomatrix lateral to the vesicle cluster is shown in yellow. The plasma membrane is depicted in green. All synaptic vesicles are shown in red. Colloidal gold particles are indicated by white spheres. Clathrin-coated endocytic intermediates are shown as flat blue discs on the plasma membrane. Bar, 100 nm.
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fig4: 3-D distribution of synapsin in stimulated reticulospinal synapse. (A) Electron micrograph of one serial section of a reticulospinal synapse stimulated at 5 Hz for 20 min, shown reconstructed in B. Synapsin is present on vesicles (v) in the filamentous cytomatrix (arrow). svc, synaptic vesicle cluster; v, vesicles in the filamentous matrix; d, dendrite; a, axoplasmic matrix. ccp, clathrin-coated pit. This arrow indicates active zone. (B) 3-D reconstruction of 10 serial ultrathin sections. The area occupied by actin-rich filamentous cytomatrix lateral to the vesicle cluster is shown in yellow. The plasma membrane is depicted in green. All synaptic vesicles are shown in red. Colloidal gold particles are indicated by white spheres. Clathrin-coated endocytic intermediates are shown as flat blue discs on the plasma membrane. Bar, 100 nm.

Mentions: In stimulated synapses, synapsin immunoreactivity was observed within the filamentous cytomatrix formed at the lateral edges of active zones during stimulation (Fig. 2 G; Fig. 4, A and B). Synapsin labeling was associated with synaptic vesicles present in the cytomatrix, which appeared to be in transit to the vesicle cluster (Fig. 2, G–I; Fig. 4, A and B). Only occasional gold particles were found at synaptic endocytic zones at rest.


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)

3-D distribution of synapsin in stimulated reticulospinal synapse. (A) Electron micrograph of one serial section of a reticulospinal synapse stimulated at 5 Hz for 20 min, shown reconstructed in B. Synapsin is present on vesicles (v) in the filamentous cytomatrix (arrow). svc, synaptic vesicle cluster; v, vesicles in the filamentous matrix; d, dendrite; a, axoplasmic matrix. ccp, clathrin-coated pit. This arrow indicates active zone. (B) 3-D reconstruction of 10 serial ultrathin sections. The area occupied by actin-rich filamentous cytomatrix lateral to the vesicle cluster is shown in yellow. The plasma membrane is depicted in green. All synaptic vesicles are shown in red. Colloidal gold particles are indicated by white spheres. Clathrin-coated endocytic intermediates are shown as flat blue discs on the plasma membrane. Bar, 100 nm.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: 3-D distribution of synapsin in stimulated reticulospinal synapse. (A) Electron micrograph of one serial section of a reticulospinal synapse stimulated at 5 Hz for 20 min, shown reconstructed in B. Synapsin is present on vesicles (v) in the filamentous cytomatrix (arrow). svc, synaptic vesicle cluster; v, vesicles in the filamentous matrix; d, dendrite; a, axoplasmic matrix. ccp, clathrin-coated pit. This arrow indicates active zone. (B) 3-D reconstruction of 10 serial ultrathin sections. The area occupied by actin-rich filamentous cytomatrix lateral to the vesicle cluster is shown in yellow. The plasma membrane is depicted in green. All synaptic vesicles are shown in red. Colloidal gold particles are indicated by white spheres. Clathrin-coated endocytic intermediates are shown as flat blue discs on the plasma membrane. Bar, 100 nm.
Mentions: In stimulated synapses, synapsin immunoreactivity was observed within the filamentous cytomatrix formed at the lateral edges of active zones during stimulation (Fig. 2 G; Fig. 4, A and B). Synapsin labeling was associated with synaptic vesicles present in the cytomatrix, which appeared to be in transit to the vesicle cluster (Fig. 2, G–I; Fig. 4, A and B). Only occasional gold particles were found at synaptic endocytic zones at rest.

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