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Syt-12 for spontaneous release

Syt-12 (green) on synaptic vesicles increases spontaneous release of neurotransmitters.

On page 113, Maximov et al. show that a calcium-independent synaptotagmin (syt) enhances the spontaneous release of neurotransmitters. By linking to another syt that does respond to calcium, the calcium-independent syt might also alter evoked neurotransmitter release.

There are many synaptotagmins, but only syt-1 and syt-2 have a well-defined function, which is to trigger the release of neurotransmitters in response to calcium. Syt-12 does not bind to calcium, yet the authors found it is still localized to synaptic vesicles.

To understand its function, the authors expressed syt-12 in cultured neurons, which did not make their own endogenous version. The presence of syt-12 increased the spontaneous release of neurotransmitter in these neurons.

The function of spontaneous release is controversial: some neuroscientists believe these release events are physiologically important for neuronal structure and function, whereas others argue that they are only a meaningless byproduct of a system that is poised to fuse many vesicles so quickly. Future syt-12 studies might address this debate.

Spontaneous release might not be syt-12's only trick, however. In synaptic vesicle fractions, syt-12 interacted with syt-1, the calcium-responsive release trigger. Syt-1 must partner with SNAREs for evoked release, but this interaction was precluded by the syt-12 association.

The authors found that calcium-evoked release worked just fine in cultured neurons in the presence of syt-12, but they note that acute and long-term changes in synaptic strength, known as plasticity, cannot be studied in this system. An animal knockout should be a better model.

Syt-12 is phosphorylated by PKA, which is necessary for plasticity, but PKA's plasticity-related targets have not been identified. Given its location, Syt-12 is a promising candidate. Its late expression in mice, only after birth, also coincides well with the onset of synaptic maturation and plasticity.

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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Related Article

Synaptotagmin-12, a synaptic vesicle phosphoprotein that modulates spontaneous neurotransmitter release

Anton Maximov, Ok-Ho Shin, Xinran Liu, and Thomas C. Südhof
J. Cell Biol. 2007 176: 113-124. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF, 851K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Related Collections Related Article Social Bookmarking                            What's this?