Ablation of All Synaptobrevin vSNAREs Blocks Evoked But Not Spontaneous Neurotransmitter Release at Neuromuscular Synapses

Yun Liu, Yoshie Sugiura, Thomas C. Südhof, Weichun Lin

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Synaptic transmission occurs when an action potential triggers neurotransmitter release via the fusion of synaptic vesicles with the presynaptic membrane, driven by the formation of SNARE complexes composed of the vesicular (v)-SNARE synaptobrevin and the target (t)-SNAREs Snap-25 and syntaxin-1. Neurotransmitters are also released spontaneously, independent of an action potential, through the fusion of synaptic vesicles with the presynaptic membrane. The major neuronal vSNAREs, synaptobrevin-1 and synaptobrevin-2, are expressed at the developing neuromuscular junction (NMJ) in mice, but their specific roles in NMJ formation and function remain unclear. Here, we examine the NMJs in mutant mouse embryos lacking either synaptobrevin 1 (Syb1lew/lew ) or synaptobrevin 2 (Syb2-/-), and those lacking both (Syb1lew/lewSyb2-/-). We found that, compared with controls: (1) the number and size of NMJs was markedly increased in Syb2-/- and Syb1lew/lewSyb2-/- mice, but not in Syb1lew/lew mice; (2) synaptic vesicle density was markedly reduced in Syb1lew/lewSyb2-/- NMJs; and (3) evoked neurotransmission was markedly reduced in Syb2-/- NMJs and completely abolished in Syb1lew/lewSyb2-/- NMJs. Surprisingly, however, spontaneous neurotransmission persists in the absence of both Syb1 and Syb2. Furthermore, spontaneous neurotransmission remains constant in Syb1lew/lewSyb2-/- NMJs despite changing Ca2+ levels. These findings reveal an overlapping role for Syb1 and Syb2 (with Syb2 being dominant) in developing NMJs in mice. Moreover, because spontaneous release becomes Ca2+-insensitive in Syb1lew/lewSyb2-/- NMJs, our findings suggest that synaptobrevin-based SNARE complexes play a critical role in conferring Ca2+ sensitivity during spontaneous release.SIGNIFICANCE STATEMENT Neurotransmitters can be released at synapses with (evoked) or without (spontaneous) the influence of action potentials. Whereas evoked neurotransmission requires Ca2+ influx, those underlying the spontaneous neurotransmission may occur with or without Ca2+ Our findings show that, in the absence neuronal vSNARE synaptobrevin-1 and synaptobrevin-2, evoked neurotransmission is completely abolished; however, spontaneous synaptic transmission not only persists but even increased. Furthermore, spontaneous synaptic transmission that is normally highly Ca2+-sensitive became Ca2+-independent upon deletion of vSNARE synaptobrevin-1 and synaptobrevin-2. These findings reveal distinct mechanisms for evoked and spontaneous neurotransmitter release. Moreover, these findings suggest that synaptobrevin-based SNARE complexes play critical roles in conferring Ca2+ sensitivity during spontaneous neurotransmission at developing neuromuscular synapses in mice.

Original languageEnglish (US)
Pages (from-to)6049-6066
Number of pages18
JournalThe Journal of neuroscience : the official journal of the Society for Neuroscience
Volume39
Issue number31
DOIs
StatePublished - Jul 31 2019

Fingerprint

R-SNARE Proteins
Vesicle-Associated Membrane Protein 2
Synaptic Transmission
Synapses
Neurotransmitter Agents
Vesicle-Associated Membrane Protein 1
SNARE Proteins
Synaptic Vesicles
Action Potentials
Neuromuscular Junction
Syntaxin 1
Membranes
Embryonic Structures

Keywords

  • evoked release
  • KO mice
  • neuromuscular junction
  • spontaneous release
  • synapse formation
  • synaptic transmission

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Ablation of All Synaptobrevin vSNAREs Blocks Evoked But Not Spontaneous Neurotransmitter Release at Neuromuscular Synapses. / Liu, Yun; Sugiura, Yoshie; Südhof, Thomas C.; Lin, Weichun.

In: The Journal of neuroscience : the official journal of the Society for Neuroscience, Vol. 39, No. 31, 31.07.2019, p. 6049-6066.

Research output: Contribution to journalArticle

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AU - Südhof, Thomas C.

AU - Lin, Weichun

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N2 - Synaptic transmission occurs when an action potential triggers neurotransmitter release via the fusion of synaptic vesicles with the presynaptic membrane, driven by the formation of SNARE complexes composed of the vesicular (v)-SNARE synaptobrevin and the target (t)-SNAREs Snap-25 and syntaxin-1. Neurotransmitters are also released spontaneously, independent of an action potential, through the fusion of synaptic vesicles with the presynaptic membrane. The major neuronal vSNAREs, synaptobrevin-1 and synaptobrevin-2, are expressed at the developing neuromuscular junction (NMJ) in mice, but their specific roles in NMJ formation and function remain unclear. Here, we examine the NMJs in mutant mouse embryos lacking either synaptobrevin 1 (Syb1lew/lew ) or synaptobrevin 2 (Syb2-/-), and those lacking both (Syb1lew/lewSyb2-/-). We found that, compared with controls: (1) the number and size of NMJs was markedly increased in Syb2-/- and Syb1lew/lewSyb2-/- mice, but not in Syb1lew/lew mice; (2) synaptic vesicle density was markedly reduced in Syb1lew/lewSyb2-/- NMJs; and (3) evoked neurotransmission was markedly reduced in Syb2-/- NMJs and completely abolished in Syb1lew/lewSyb2-/- NMJs. Surprisingly, however, spontaneous neurotransmission persists in the absence of both Syb1 and Syb2. Furthermore, spontaneous neurotransmission remains constant in Syb1lew/lewSyb2-/- NMJs despite changing Ca2+ levels. These findings reveal an overlapping role for Syb1 and Syb2 (with Syb2 being dominant) in developing NMJs in mice. Moreover, because spontaneous release becomes Ca2+-insensitive in Syb1lew/lewSyb2-/- NMJs, our findings suggest that synaptobrevin-based SNARE complexes play a critical role in conferring Ca2+ sensitivity during spontaneous release.SIGNIFICANCE STATEMENT Neurotransmitters can be released at synapses with (evoked) or without (spontaneous) the influence of action potentials. Whereas evoked neurotransmission requires Ca2+ influx, those underlying the spontaneous neurotransmission may occur with or without Ca2+ Our findings show that, in the absence neuronal vSNARE synaptobrevin-1 and synaptobrevin-2, evoked neurotransmission is completely abolished; however, spontaneous synaptic transmission not only persists but even increased. Furthermore, spontaneous synaptic transmission that is normally highly Ca2+-sensitive became Ca2+-independent upon deletion of vSNARE synaptobrevin-1 and synaptobrevin-2. These findings reveal distinct mechanisms for evoked and spontaneous neurotransmitter release. Moreover, these findings suggest that synaptobrevin-based SNARE complexes play critical roles in conferring Ca2+ sensitivity during spontaneous neurotransmission at developing neuromuscular synapses in mice.

AB - Synaptic transmission occurs when an action potential triggers neurotransmitter release via the fusion of synaptic vesicles with the presynaptic membrane, driven by the formation of SNARE complexes composed of the vesicular (v)-SNARE synaptobrevin and the target (t)-SNAREs Snap-25 and syntaxin-1. Neurotransmitters are also released spontaneously, independent of an action potential, through the fusion of synaptic vesicles with the presynaptic membrane. The major neuronal vSNAREs, synaptobrevin-1 and synaptobrevin-2, are expressed at the developing neuromuscular junction (NMJ) in mice, but their specific roles in NMJ formation and function remain unclear. Here, we examine the NMJs in mutant mouse embryos lacking either synaptobrevin 1 (Syb1lew/lew ) or synaptobrevin 2 (Syb2-/-), and those lacking both (Syb1lew/lewSyb2-/-). We found that, compared with controls: (1) the number and size of NMJs was markedly increased in Syb2-/- and Syb1lew/lewSyb2-/- mice, but not in Syb1lew/lew mice; (2) synaptic vesicle density was markedly reduced in Syb1lew/lewSyb2-/- NMJs; and (3) evoked neurotransmission was markedly reduced in Syb2-/- NMJs and completely abolished in Syb1lew/lewSyb2-/- NMJs. Surprisingly, however, spontaneous neurotransmission persists in the absence of both Syb1 and Syb2. Furthermore, spontaneous neurotransmission remains constant in Syb1lew/lewSyb2-/- NMJs despite changing Ca2+ levels. These findings reveal an overlapping role for Syb1 and Syb2 (with Syb2 being dominant) in developing NMJs in mice. Moreover, because spontaneous release becomes Ca2+-insensitive in Syb1lew/lewSyb2-/- NMJs, our findings suggest that synaptobrevin-based SNARE complexes play a critical role in conferring Ca2+ sensitivity during spontaneous release.SIGNIFICANCE STATEMENT Neurotransmitters can be released at synapses with (evoked) or without (spontaneous) the influence of action potentials. Whereas evoked neurotransmission requires Ca2+ influx, those underlying the spontaneous neurotransmission may occur with or without Ca2+ Our findings show that, in the absence neuronal vSNARE synaptobrevin-1 and synaptobrevin-2, evoked neurotransmission is completely abolished; however, spontaneous synaptic transmission not only persists but even increased. Furthermore, spontaneous synaptic transmission that is normally highly Ca2+-sensitive became Ca2+-independent upon deletion of vSNARE synaptobrevin-1 and synaptobrevin-2. These findings reveal distinct mechanisms for evoked and spontaneous neurotransmitter release. Moreover, these findings suggest that synaptobrevin-based SNARE complexes play critical roles in conferring Ca2+ sensitivity during spontaneous neurotransmission at developing neuromuscular synapses in mice.

KW - evoked release

KW - KO mice

KW - neuromuscular junction

KW - spontaneous release

KW - synapse formation

KW - synaptic transmission

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