Tomosyn inhibits synaptic vesicle priming in Caenorhabditis elegans.
Caenorhabditis elegans TOM-1 is orthologous to vertebrate tomosyn, a cytosolic syntaxin-binding protein implicated in the modulation of both constitutive and regulated exocytosis. To investigate how TOM-1 regulates exocytosis of synaptic vesicles in vivo, we analyzed C. elegans tom-1 mutants. Our electrophysiological analysis indicates that evoked postsynaptic responses at tom-1 mutant synapses are prolonged leading to a two-fold increase in total charge transfer. The enhanced response in tom-1 mutants is not associated with any detectable changes in postsynaptic response kinetics, neuronal outgrowth, or synaptogenesis. However, at the ultrastructural level, we observe a concomitant increase in the number of plasma membrane-contacting vesicles in tom-1 mutant synapses, a phenotype reversed by neuronal expression of TOM-1. Priming defective unc-13 mutants show a dramatic reduction in plasma membrane-contacting vesicles, suggesting these vesicles largely represent the primed vesicle pool at the C. elegans neuromuscular junction. Consistent with this conclusion, hyperosmotic responses in tom-1 mutants are enhanced, indicating the primed vesicle pool is enhanced. Furthermore, the synaptic defects of unc-13 mutants are partially suppressed in tom-1 unc-13 double mutants. These data indicate that in the intact nervous system, TOM-1 negatively regulates synaptic vesicle priming.
Gracheva
Elena O
EO
Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA.
Burdina
Anna O
AO
Holgado
Andrea M
AM
Berthelot-Grosjean
Martine
M
Ackley
Brian D
BD
Hadwiger
Gayla
G
Nonet
Michael L
ML
Weimer
Robby M
RM
Richmond
Janet E
JE
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D004594:Electrophysiology; D008969:Molecular Sequence Data; D009154:Mutation; D009469:Neuromuscular Junction / Q000502:physiology; D010641:Phenotype; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics / Q000502:physiology; D016415:Sequence Alignment; D013572:Synaptic Vesicles / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure
D029742:Caenorhabditis elegans Proteins; D020033:Protein Isoforms; C513301:tom-1 protein, C elegans