Rieckhof Gabrielle E, Yoshihara Motojiro, Guan Zhuo, Littleton J Troy
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Biol Chem. 2003 Oct 17;278(42):41099-108. doi: 10.1074/jbc.M306417200. Epub 2003 Aug 1.
Voltage-gated calcium channels couple changes in membrane potential to neuronal functions regulated by calcium, including neurotransmitter release. Here we report that presynaptic N-type calcium channels not only control neurotransmitter release but also regulate synaptic growth at Drosophila neuromuscular junctions. In a screen for behavioral mutants that disrupt synaptic transmission, an allele of the N-type calcium channel locus (Dmca1A) was identified that caused synaptic undergrowth. The underlying molecular defect was identified as a neutralization of a charged residue in the third S4 voltage sensor. RNA interference reduction of N-type calcium channel expression also reduced synaptic growth. Hypomorphic mutations in syntaxin-1A or n-synaptobrevin, which also disrupt neurotransmitter release, did not affect synapse proliferation at the neuromuscular junction, suggesting calcium entry through presynaptic N-type calcium channels, not neurotransmitter release per se, is important for synaptic growth. The reduced synapse proliferation in Dmca1A mutants is not due to increased synapse retraction but instead reflects a role for calcium influx in synaptic growth mechanisms. These results suggest N-type channels participate in synaptic growth through signaling pathways that are distinct from those that mediate neurotransmitter release. Linking presynaptic voltage-gated calcium entry to downstream calcium-sensitive synaptic growth regulators provides an efficient activity-dependent mechanism for modifying synaptic strength.
电压门控钙通道将膜电位变化与受钙调节的神经元功能相偶联，这些功能包括神经递质释放。我们在此报告，突触前N型钙通道不仅控制神经递质释放，还调节果蝇神经肌肉接头处的突触生长。在对破坏突触传递的行为突变体进行的筛选中，鉴定出一个N型钙通道基因座（Dmca1A）的等位基因，它导致突触生长不足。潜在的分子缺陷被确定为第三个S4电压感受器中一个带电残基的中和。RNA干扰降低N型钙通道表达也会减少突触生长。Syntaxin-1A或n-突触囊泡蛋白的亚等位基因突变也会破坏神经递质释放，但不影响神经肌肉接头处的突触增殖，这表明通过突触前N型钙通道的钙内流而非神经递质释放本身对突触生长很重要。Dmca1A突变体中突触增殖减少并非由于突触回缩增加，而是反映了钙内流在突触生长机制中的作用。这些结果表明，N型通道通过与介导神经递质释放的信号通路不同的信号通路参与突触生长。将突触前电压门控钙内流与下游钙敏感的突触生长调节因子联系起来，为调节突触强度提供了一种有效的活动依赖性机制。
