Synaptotagmin I is necessary for compensatory synaptic vesicle endocytosis in vivo

Nature. 2003 Dec 4;426(6966):559-63. doi: 10.1038/nature02184. Epub 2003 Nov 23.


Neurotransmission requires a balance of synaptic vesicle exocytosis and endocytosis. Synaptotagmin I (Syt I) is widely regarded as the primary calcium sensor for synaptic vesicle exocytosis. Previous biochemical data suggest that Syt I may also function during synaptic vesicle endocytosis; 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. 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.

MeSH terms

  • Animals
  • Calcium-Binding Proteins*
  • Drosophila melanogaster / cytology*
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / metabolism*
  • Endocytosis*
  • Gene Deletion
  • Green Fluorescent Proteins
  • Hydrogen-Ion Concentration
  • Kinetics
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Membrane Fusion
  • Membrane Glycoproteins / deficiency
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Nerve Tissue Proteins / deficiency
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Neurotransmitter Agents / metabolism
  • Synaptic Vesicles / metabolism*
  • Synaptotagmin I
  • Synaptotagmins


  • Calcium-Binding Proteins
  • Luminescent Proteins
  • Membrane Glycoproteins
  • Nerve Tissue Proteins
  • Neurotransmitter Agents
  • Synaptotagmin I
  • Synaptotagmins
  • Green Fluorescent Proteins