Synaptic UNC13A protein variant causes increased neurotransmission and dyskinetic movement disorder
Noa Lipstein, … , Judith J. Jans, Nils Brose
Noa Lipstein, … , Judith J. Jans, Nils Brose
Published February 13, 2017
Citation Information: J Clin Invest. 2017;127(3):1005-1018. https://doi.org/10.1172/JCI90259.
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Research Article Neuroscience

Synaptic UNC13A protein variant causes increased neurotransmission and dyskinetic movement disorder

Abstract

Munc13 proteins are essential regulators of neurotransmitter release at nerve cell synapses. They mediate the priming step that renders synaptic vesicles fusion-competent, and their genetic elimination causes a complete block of synaptic transmission. Here we have described a patient displaying a disorder characterized by a dyskinetic movement disorder, developmental delay, and autism. Using whole-exome sequencing, we have shown that this condition is associated with a rare, de novo Pro814Leu variant in the major human Munc13 paralog UNC13A (also known as Munc13-1). Electrophysiological studies in murine neuronal cultures and functional analyses in Caenorhabditis elegans revealed that the UNC13A variant causes a distinct dominant gain of function that is characterized by increased fusion propensity of synaptic vesicles, which leads to increased initial synaptic vesicle release probability and abnormal short-term synaptic plasticity. Our study underscores the critical importance of fine-tuned presynaptic control in normal brain function. Further, it adds the neuronal Munc13 proteins and the synaptic vesicle priming process that they control to the known etiological mechanisms of psychiatric and neurological synaptopathies.

Authors

Noa Lipstein, Nanda M. Verhoeven-Duif, Francesco E. Michelassi, Nathaniel Calloway, Peter M. van Hasselt, Katarzyna Pienkowska, Gijs van Haaften, Mieke M. van Haelst, Ron van Empelen, Inge Cuppen, Heleen C. van Teeseling, Annemieke M.V. Evelein, Jacob A. Vorstman, Sven Thoms, Olaf Jahn, Karen J. Duran, Glen R. Monroe, Timothy A. Ryan, Holger Taschenberger, Jeremy S. Dittman, Jeong-Seop Rhee, Gepke Visser, Judith J. Jans, Nils Brose

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Figure 2

Munc13-1P827L increases synaptic strength.

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Munc13-1P827L increases synaptic strength. (A) Example traces of initial...
(A) Example traces of initial, evoked excitatory postsynaptic currents (EPSCs) from autaptic hippocampal Munc13-1 Munc13-2 DKO neurons expressing Munc13-1WT (black, left) or Munc13-1P827L (red, left), and of evoked inhibitory postsynaptic currents (IPSCs) from striatal Munc13-1 Munc13-2 DKO neurons expressing Munc13-1WT (black, right) or Munc13-1P827L (blue, right). (B) Average EPSC and IPSC amplitudes as in A. Individual average values per neuron are indicated as circles (left: hippocampal neurons; black, Munc13-1WT; red, Munc13-1P827L, P < 0.01) or squares (right: striatal neurons; black, Munc13-1WT; blue, Munc13-1P827L, P > 0.05); Mann-Whitney test. (C) Example traces of EPSCs in hippocampal Munc13-1 Munc13-2 DKO neurons expressing Munc13-1WT (black) or Munc13-1P827L (red), measured at 35°C–37°C and in 2 mM Ca2+/1 mM Mg2+. (D) Average EPSC amplitudes as in C. Individual average values per neuron are indicated as circles; P < 0.01; Mann-Whitney test. (E) Amino acid sequence alignment of murine Munc13-1 and of C. elegans UNC-13L. Red letters indicate Pro827 in Munc13-1 and Pro956 in UNC-13. (F and G) Plot depicting the percentage of WT (open circles, n = 11) and transgenic worms [black circles, UNC-13L(WT) in unc-13(–), n = 10; red circles, UNC-13L(P/L) in unc-13(–), n = 10] paralyzed as a function of the time following exposure to 1 mM aldicarb (F), and quantification of the percentage of worms paralyzed after 60 minutes of exposure to 1 mM aldicarb (G). Neuronal transgenes (Tg) are WT UNC-13L [UNC-13L(WT)], UNC-13L(P/L), and no transgene (X). Genetic background is indicated as WT (+) or unc-13(s69) null mutant (–), n = 10–11, P < 0.01; ANOVA statistics and Tukey-Kramer test for multiple comparisons. All error bars in the figure represent mean ± SEM. **P < 0.01, ***P < 0.001; NS, P > 0.05. See Table 2 for further details.