Directionality of the actin filament assembly in the synaptic endocytic zone.

CAPANI, F.; ANDERSSON, F; CRUM, J; LILLIG, C ; TOMILIN, N; EVERGREN, E. ; ELLISMAN, M; BRODIN, L.; SHUPLIAKOV, O

Congreso; Meeting of the American Society for Neuroscience; 2014

SFN

Actin is an abundant component of the pre-synaptic machinery that has been implicated in anchoring, exocytosis and recycling of synaptic vesicles. However, the mechanisms involving actin remain still unclear. By combining presynaptic microinjections with subsequent microscopic analysis we investigated the directionality of actin filaments assembly in the synaptic endocytic zone. Experiments were performed in the giant reticulospinal axon synapse in lamprey. Excessive amounts of Alexa-tagged phalloidin were microinjected into giant axons to assure stabilization of actin filaments during synaptic vesicle recycling at resting conditions and after 5 Hz stimulation. Under resting conditions, confocal images showed a weak accumulation of fluorescence in ring-like structures around active zones. Fluorescence intensity of these structures increased during stimulation and followed by an outgrowth of F-actin outside the ring-like area. At subcellular level, bundles of filaments could be traced from the endocytic area to the cluster. They were identified as actin filaments with actin specific antibodies. Synaptic vesicles were attached to the bundles. Prolonged stimulation resulted in complete disassembly of the vesicle clusters; vesicles were located outside synaptic areas. These results provide support to the view that active dynamic changes in actin cytoskeleton occurs during synaptic vesicle recycling and control proper migration of synaptic vesicles at the endocytic zone.