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UNC-13 is required for synaptic vesicle fusion in C. elegans

Abstract

We analyzed the synaptic physiology of unc-13 mutants in the nematode C. elegans. Mutants of unc-13 had normal nervous system architecture, and the densities of synapses and postsynaptic receptors were normal at the neuromuscular junction. However, the number of synaptic vesicles at neuromuscular junctions was two- to threefold greater in unc-13 mutants than in wild-type animals. Most importantly, evoked release at both GABAergic and cholinergic synapses was almost absent in unc-13 null alleles, as determined by whole-cell, voltage-clamp techniques. Although mutant synapses had morphologically docked vesicles, these vesicles were not competent for release as assayed by spontaneous release in calcium-free solution or by the application of hyperosmotic saline. These experiments support models in which UNC-13 mediates either fusion of vesicles during exocytosis or priming of vesicles for fusion.

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Figure 1: Domain structure of UNC-13, indicating the location of the mutations used in this study.
Figure 2: GABAergic motor neuron anatomy is normal in unc-13 mutants.
Figure 3: The density and distribution of neuromuscular synapses is normal in unc-13 mutants.
Figure 4: Synaptic vesicles accumulate in unc-13 mutants.
Figure 5: Evoked responses are reduced in unc-13 mutants.
Figure 6: Endogenous release of synaptic vesicles is reduced in unc-13 mutants.
Figure 8: Release of synaptic vesicles is reduced in response to hyperosmotic media in unc-13 mutants.
Figure 7: Calcium-free miniature postsynaptic events are severely reduced in unc-13 mutants.

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Acknowledgements

We thank Becky Kohn and Jim Rand for sharing unpublished data. We thank Bharathi Aravamudan, Tim Fergestad and Kendal Broadie for interactions and discussions. We thank Wayne Davis, Doj Yoshikami and Karen Yook for comments on the manuscript. Rob Weimer provided confocal images, and Ann Rose provided the s69 allele. This work was supported by NIH grants RO3 MHS9820-01 (J.E.R.) and RO1 NS34307 (E.M.J.) and by the Damon Runyon Fund. Strains were obtained from the Caenorhabditis Genetics Center.

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Correspondence to Erik M. Jorgensen.

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Richmond, J., Davis, W. & Jorgensen, E. UNC-13 is required for synaptic vesicle fusion in C. elegans. Nat Neurosci 2, 959–964 (1999). https://doi.org/10.1038/14755

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