Journal
NATURE
Volume 426, Issue 6966, Pages 559-563Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nature02184
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Neurotransmission requires a balance of synaptic vesicle exocytosis and endocytosis(1). Synaptotagmin I (Syt I) is widely regarded as the primary calcium sensor for synaptic vesicle exocytosis(2-6). Previous biochemical data suggest that Syt I may also function during synaptic vesicle endocytosis(7-16); however, ultrastructural analyses at synapses with impaired Syt I function have provided an indirect and conflicting view of the role of Syt I during synaptic vesicle endocytosis(3,8-10,14). Until now it has not been possible experimentally to separate the exocytic and endocytic functions of Syt I in vivo. Here, we test directly the role of Syt I during endocytosis in vivo. We use quantitative live imaging of a pH-sensitive green fluorescent protein fused to a synaptic vesicle protein (synapto-pHluorin) to measure the kinetics of endocytosis in sytI-null Drosophila. We then combine live imaging of the synapto-pHluorins with photoinactivation of Syt I, through fluorescein-assisted light inactivation, after normal Syt I-mediated vesicle exocytosis. By inactivating Syt I only during endocytosis, we demonstrate that Syt I is necessary for the endocytosis of synaptic vesicles that have undergone exocytosis using a functional Syt I protein.
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