The JIP3 scaffold protein UNC-16 regulates RAB-5 dependent membrane trafficking at C. elegans synapses

Dev Neurobiol. 2009 Feb;69(2-3):174-90. doi: 10.1002/dneu.20690.


How endosomes contribute to the maintenance of vesicular structures at presynaptic terminals remains controversial and poorly understood. Here, we have investigated synaptic endosomal compartments in the presynaptic terminals of C. elegans GABAergic motor neurons. Using RAB reporters, we find that several subsynaptic compartments reside in, or near, presynaptic regions. Loss of function in the C. elegans JIP3 protein, UNC-16, causes a RAB-5-containing compartment to accumulate abnormally at presynaptic terminals. Ultrastructural analysis shows that synapses in unc-16 mutants contain reduced number of synaptic vesicles, accompanied by an increase in the size and number of cisternae. FRAP analysis revealed a slow recovery of RAB-5 in unc-16 mutants, suggestive of an impairment of RAB-5 activity state and local vesicular trafficking. Overexpression of RAB-5:GDP partially suppresses, whereas overexpression of RAB-5:GTP enhances, the synaptic defects of unc-16 mutants. Our data demonstrate a novel function of UNC-16 in the regulation of synaptic membrane trafficking and suggest that the synaptic RAB-5 compartment contributes to synaptic vesicle biogenesis or maintenance.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / physiology*
  • Animals
  • Animals, Genetically Modified
  • Caenorhabditis elegans / anatomy & histology
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism
  • Caenorhabditis elegans Proteins / physiology*
  • Endocytosis / genetics
  • Guanosine Diphosphate / metabolism
  • Luminescent Proteins / genetics
  • Microscopy, Confocal / methods
  • Mutation / genetics
  • Presynaptic Terminals / metabolism*
  • Presynaptic Terminals / ultrastructure
  • Synaptic Membranes / genetics
  • Synaptic Membranes / metabolism*
  • Synaptic Membranes / ultrastructure
  • Synaptic Vesicles / genetics
  • Synaptic Vesicles / metabolism
  • Synaptic Vesicles / ultrastructure
  • Time Factors
  • rab5 GTP-Binding Proteins / genetics
  • rab5 GTP-Binding Proteins / metabolism*


  • Adaptor Proteins, Signal Transducing
  • Caenorhabditis elegans Proteins
  • Luminescent Proteins
  • unc-16 protein, C elegans
  • Guanosine Diphosphate
  • rab5 GTP-Binding Proteins