title: Colocalization of synapsin and actin during synaptic vesicle recycling.
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.
authors.affiliation: The Rockefeller University, New York, NY 10021, USA. ona@chronos.med.yale.edu
authors.forename: Ona
authors.initials: O
authors.lastname: Bloom
authors.forename: Emma
authors.initials: E
authors.lastname: Evergren
authors.forename: Nikolay
authors.initials: N
authors.lastname: Tomilin
authors.forename: Ole
authors.initials: O
authors.lastname: Kjaerulff
authors.forename: Peter
authors.initials: P
authors.lastname: Löw
authors.forename: Lennart
authors.initials: L
authors.lastname: Brodin
authors.forename: Vincent A
authors.initials: VA
authors.lastname: Pieribone
authors.forename: Paul
authors.initials: P
authors.lastname: Greengard
authors.forename: Oleg
authors.initials: O
authors.lastname: Shupliakov
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D004705:Endocytosis; D007798:Lampreys / Q000378:metabolism*; D008845:Microinjections; D016253:Microscopy, Immunoelectron; D008954:Models, Biological; D013116:Spinal Cord / Q000378:metabolism / Q000648:ultrastructure; D013569:Synapses / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D016704:Synapsins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D000199:Actins; D016704:Synapsins