Tomosyn negatively regulates CAPS-dependent peptide release at Caenorhabditis elegans synapses.
The syntaxin-interacting protein tomosyn is thought to be a key regulator of exocytosis, although its precise mechanism of action has yet to be elucidated. Here we examined the role of tomosyn in peptide secretion in Caenorhabditis elegans tomosyn (tom-1) mutants. Ultrastructural analysis of tom-1 mutants revealed a 50% reduction in presynaptic dense-core vesicles (DCVs) corresponding to enhanced neuropeptide release. Conversely, overexpression of TOM-1 led to an accumulation of DCVs. Together, these data provide the first in vivo evidence that TOM-1 negatively regulates DCV exocytosis. In C. elegans, neuropeptide release is promoted by the calcium-dependent activator protein for secretion (CAPS) homolog UNC-31. To test for a genetic interaction between tomosyn and CAPS, we generated tom-1;unc-31 double mutants. Loss of TOM-1 suppressed the behavioral, electrophysiological, and DCV ultrastructural phenotypes of unc-31 mutants, indicating that TOM-1 antagonizes UNC-31-dependent DCV release. Because unc-31 mutants exhibit synaptic transmission defects, we postulated that loss of DCV release in these mutants and the subsequent suppression by tom-1 mutants could simply reflect alterations in synaptic activity, rather than direct regulation of DCV release. To distinguish between these two possibilities, we analyzed C. elegans Rim mutants (unc-10), which have a comparable reduction in synaptic transmission to unc-31 mutants, specifically attributed to defects in synaptic vesicle (SV) exocytosis. Based on this analysis, we conclude that the changes in DCV release in tom-1 and unc-31 mutants reflect direct effects of TOM-1 and UNC-31 on DCV exocytosis, rather than altered SV release.
Gracheva
Elena O
EO
Department of Biological Sciences, Science and Engineering Labs, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
Burdina
Anna O
AO
Touroutine
Denis
D
Berthelot-Grosjean
Martine
M
Parekh
Hetal
H
Richmond
Janet E
JE
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000502:physiology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology*; D009154:Mutation; D010455:Peptides / Q000037:antagonists & inhibitors / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure
D029742:Caenorhabditis elegans Proteins; D002147:Calmodulin; D010455:Peptides; C513301:tom-1 protein, C elegans