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Synaptotagmin-1 functions as a Ca2+ sensor for spontaneous release

Nature Neuroscience volume 12, pages 759–766 (2009)Cite this article

Abstract

Spontaneous 'mini' release occurs at all synapses, but its nature remains enigmatic. We found that >95% of spontaneous release in murine cortical neurons was induced by Ca2+-binding to synaptotagmin-1 (Syt1), the Ca2+ sensor for fast synchronous neurotransmitter release. Thus, spontaneous and evoked release used the same Ca2+-dependent release mechanism. As a consequence, Syt1 mutations that altered its Ca2+ affinity altered spontaneous and evoked release correspondingly. Paradoxically, Syt1 deletions (as opposed to point mutations) massively increased spontaneous release. This increased spontaneous release remained Ca2+ dependent but was activated at lower Ca2+ concentrations and with a lower Ca2+ cooperativity than synaptotagmin-driven spontaneous release. Thus, in addition to serving as a Ca2+ sensor for spontaneous and evoked release, Syt1 clamped a second, more sensitive Ca2+ sensor for spontaneous release that resembles the Ca2+ sensor for evoked asynchronous release. These data suggest that Syt1 controls both evoked and spontaneous release at a synapse as a simultaneous Ca2+-dependent activator and clamp of exocytosis.

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Figure 1: Spontaneous miniature release is Ca2+ dependent in wild-type and Syt1 knockout synapses.
Figure 2: Enhanced frequency, increased apparent Ca2+ affinity and decreased Ca2+ cooperativity of spontaneous release in Syt1−/− synapses.
Figure 3: Knockin mutations altering the apparent Ca2+ affinity of Syt1 cause corresponding changes in the apparent Ca2+ affinity of evoked release.
Figure 4: Knockin mutations altering the apparent Ca2+ affinity of Syt1 cause corresponding changes in the apparent Ca2+ affinity of spontaneous release.
Figure 5: Knockin mutations in Syt1 alter spontaneous release monitored in acute slices.
Figure 6: Syt1 clamping of spontaneous release requires intact Syt1 Ca2+-binding sites.
Figure 7: Membrane proximity of Syt1 C2 domains contributes to evoked, but not spontaneous, release.

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Acknowledgements

We thank I. Kornblum, J. Mitchell, L. Fan and A. Roth for excellent technical assistance, and A. Maximov and C. Zhang for advice.

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Author notes

  1. Jun Xu & Ok-Ho Shin

    Present address: Present address: GlaxoSmithKline (China) R&D Co. Pudong, Shanghai, China (J.X.), and Department of Neuroscience & Cell Biology, University of Texas Medical Branch, Galveston, Texas, USA (O.-H.S.).,

Authors and Affiliations

  1. Department of Molecular & Cellular Physiology, Stanford University, Palo Alto, California, USA

    Jun Xu, Zhiping P Pang & Thomas C Südhof

  2. Howard Hughes Medical Institute, Stanford University, Palo Alto, California, USA

    Jun Xu, Zhiping P Pang & Thomas C Südhof

  3. Department of Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas, USA

    Jun Xu, Zhiping P Pang, Ok-Ho Shin & Thomas C Südhof

  4. Howard Hughes Medical Institute, The University of Texas Southwestern Medical Center, Dallas, Texas, USA

    Jun Xu, Zhiping P Pang & Thomas C Südhof

  5. Department of Molecular Genetics, The University of Texas Southwestern Medical Center, Dallas, Texas, USA

    Thomas C Südhof

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  1. Jun Xu
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Contributions

J.X., Z.P.P. and O.-H.S. planned, performed and analyzed the experiments. T.C.S. conceived the project, supervised the experiments and wrote the paper.

Corresponding author

Correspondence to Thomas C Südhof.

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Xu, J., Pang, Z., Shin, OH. et al. Synaptotagmin-1 functions as a Ca2+ sensor for spontaneous release. Nat Neurosci 12, 759–766 (2009). https://doi.org/10.1038/nn.2320

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