National Centre for Biological Sciences, Bangalore 560065, India, Institute for Clinical Neurobiology, University of Würzburg, 97078 Würzburg, Germany, Department of Genetics for Learning and Memory, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany, School of Genetics and Microbiology, School of Natural Sciences, Smurfit Institute of Genetics and Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin-2, Ireland.
J Neurosci. 2013 Oct 16;33(42):16576-85. doi: 10.1523/JNEUROSCI.3142-13.2013.
In Drosophila, short-term (STH) and long-term habituation (LTH) of olfactory avoidance behavior are believed to arise from the selective potentiation of GABAergic synapses between multiglomerular local circuit interneurons (LNs) and projection neurons in the antennal lobe. However, the underlying mechanisms remain poorly understood. Here, we show that synapsin (syn) function is necessary for STH and that syn(97)-null mutant defects in STH can be rescued by syn(+) cDNA expression solely in the LN1 subset of GABAergic local interneurons. As synapsin is a synaptic vesicle-clustering phosphoprotein, these observations identify a presynaptic mechanism for STH as well as the inhibitory interneurons in which this mechanism is deployed. Serine residues 6 and/or 533, potential kinase target sites of synapsin, are necessary for synapsin function suggesting that synapsin phosphorylation is essential for STH. Consistently, biochemical analyses using a phospho-synapsin-specific antiserum show that synapsin is a target of Ca(2+) calmodulin-dependent kinase II (CaMKII) phosphorylation in vivo. Additional behavioral and genetic observations demonstrate that CaMKII function is necessary in LNs for STH. Together, these data support a model in which CaMKII-mediated synapsin phosphorylation in LNs induces synaptic vesicle mobilization and thereby presynaptic facilitation of GABA release that underlies olfactory STH. Finally, the striking observation that LTH occurs normally in syn(97) mutants indicates that signaling pathways for STH and LTH diverge upstream of synapsin function in GABAergic interneurons.
在果蝇中，嗅觉回避行为的短期（STH）和长期习惯化（LTH）被认为是由于多肾小球局部回路中间神经元（LN）和触角叶投射神经元之间 GABA 能突触的选择性增强而产生的。然而，其潜在的机制仍知之甚少。在这里，我们表明突触素（syn）功能对于 STH 是必要的，并且 syn(97)-null 突变体在 STH 中的缺陷可以通过仅在 GABA 能局部中间神经元的 LN1 亚群中表达 syn(+)cDNA 来挽救。由于突触素是一种突触小泡聚集磷酸蛋白，这些观察结果确定了 STH 的一个突触前机制，以及该机制所部署的抑制性中间神经元。突触素的丝氨酸残基 6 和/或 533 是突触素功能的潜在激酶靶位，表明突触素磷酸化对于 STH 是必不可少的。一致地，使用磷酸化突触素特异性抗血清的生化分析表明，突触素是 Ca(2+)钙调蛋白依赖性激酶 II（CaMKII）在体内磷酸化的靶标。额外的行为和遗传观察表明，CaMKII 功能在 LN 中对于 STH 是必要的。总之，这些数据支持了这样一个模型，即 CaMKII 介导的 LN 中突触素磷酸化诱导突触小泡的动员，从而导致 GABA 释放的突触前易化，这是嗅觉 STH 的基础。最后，令人惊讶的观察结果表明，在 syn(97)突变体中正常发生 LTH，表明 STH 和 LTH 的信号通路在 GABA 能中间神经元中突触素功能的上游是不同的。
