Synaptotagmin-2 is essential for survival and contributes to Ca2+ triggering of neurotransmitter release in central and neuromuscular synapses

Center for Basic Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 01/2007; 26(52):13493-504. DOI: 10.1523/JNEUROSCI.3519-06.2006
Source: PubMed

ABSTRACT Biochemical and genetic data suggest that synaptotagmin-2 functions as a Ca2+ sensor for fast neurotransmitter release in caudal brain regions, but animals and/or synapses lacking synaptotagmin-2 have not been examined. We have now generated mice in which the 5' end of the synaptotagmin-2 gene was replaced by lacZ. Using beta-galactosidase as a marker, we show that, consistent with previous studies, synaptotagmin-2 is widely expressed in spinal cord, brainstem, and cerebellum, but is additionally present in selected forebrain neurons, including most striatal neurons and some hypothalamic, cortical, and hippocampal neurons. Synaptotagmin-2-deficient mice were indistinguishable from wild-type littermates at birth, but subsequently developed severe motor dysfunction, and perished at approximately 3 weeks of age. Electrophysiological studies in cultured striatal neurons revealed that the synaptotagmin-2 deletion slowed the kinetics of evoked neurotransmitter release without altering the total amount of release. In contrast, synaptotagmin-2-deficient neuromuscular junctions (NMJs) suffered from a large reduction in evoked release and changes in short-term synaptic plasticity. Furthermore, in mutant NMJs, the frequency of spontaneous miniature release events was increased both at rest and during stimulus trains. Viewed together, our results demonstrate that the synaptotagmin-2 deficiency causes a lethal impairment in synaptic transmission in selected synapses. This impairment, however, is less severe than that produced in forebrain neurons by deletion of synaptotagmin-1, presumably because at least in NMJs, synaptotagmin-1 is coexpressed with synaptotagmin-2, and both together mediate fast Ca2+-triggered release. Thus, synaptotagmin-2 is an essential synaptotagmin isoform that functions in concert with other synaptotagmins in the Ca2+ triggering of neurotransmitter release.

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Available from: Yun Liu, Aug 16, 2015
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    • "However, no evidence was found for an involvement of SNAP-25 in the phorbol ester potentiation of synaptic transmission in hippocampal neurons (Finley et al., 2003), and the PKC/CaM kinase consensus site in Syt1 is not conserved in Syt2 (Nagy et al., 2006). Since robust PTP is also observed at synapses which express Syt2 as their main Ca 2+ sensor, like the calyx of Held and neuromuscular synapses (Pang et al., 2006), Syt1 is unlikely a general phosphorylation target for the induction of PTP. Second, ion channels like voltage-gated K + channels and Ca 2+ channels are targets of PKC phosphorylation (Zamponi et al., 1997; Song et al., 2005). "
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    • "Under our experimental conditions, SYT1 distribution was similar at glutamatergic and GABAergic terminals, whereas SYT2 expression was more robust in GABAergic terminals. The latter finding extend quantitatively the results of previous studies showing an association between SYT2 and GABAergic neurons (Pang et al., 2006a; Fox and Sanes, 2007). As synapses expressing SYT2 display a faster transmitter release than those expressing SYT1 (Xu et al., 2007), it is conceivable that expression of a given SYT isoform contributes to specific release properties. "
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    • "Instead, it measures the intrinsic Ca 2+ sensitivity of transmitter release, and its value ranges from 1 to 5 across different preparations (Augustine et al., 1985; Augustine and Charlton, 1986; Bollmann et al., 2000; Borst and Sakmann, 1996; Brandt et al., 2005; Dodge and Rahamimoff, 1967; Duncan et al., 2010; Llinás et al., 1981; Mintz et al., 1995; Reid et al., 1998; Schneggenburger and Neher, 2000; Stanley, 1986). Values of n greater than one obtained in many synapses suggest that exocytosis requires the binding of several Ca 2+ ions to proteins gating release, possibly Synaptotagmin , a well-described Ca 2+ sensing protein that is also a component of the SNARE protein complex, and plays a key role in the gating of transmitter release (Fernandez-Chacon et al., 2001; Geppert et al., 1994; Nagy et al., 2006; Pang et al., 2006; Stevens and Sullivan, 2003; Xu et al., 2007). Isoforms 1, 2, and 9 all have five Ca 2+ binding sites, with three on the C2A domain and two on the C2B domain of the protein (see Rizo and Rosenmund, 2008 for review). "
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