Key Laboratory for Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
J Neurosci. 2010 Sep 1;30(35):11624-34. doi: 10.1523/JNEUROSCI.0410-10.2010.
Synapse remodeling is a widespread and fundamental process that underlies the formation of neuronal circuitry during development and in adaptation to physiological and/or environmental changes. However, the mechanisms of synapse remodeling are poorly understood. Synapses at the neuromuscular junction (NMJ) in Drosophila larvae undergo dramatic and extensive remodeling during metamorphosis to generate adult-specific synapses. To explore the molecular and cellular processes of synapse elimination, we performed confocal microscopy, live imaging, and electron microscopy (EM) of NMJ synapses during the early stages of metamorphosis in Drosophila in which the expressions of selected genes were genetically altered. We report that the localization of the postsynaptic scaffold protein Disc large (Dlg) becomes diffuse first and then undetectable, as larval muscles undergo histolysis, whereas presynaptic vesicles aggregate and are retrogradely transported along axons in synchrony with the formation of filopodia-like structures along NMJ elaborations and retraction of the presynaptic plasma membrane. EM revealed that the postsynaptic subsynaptic reticulum vacuolizes in the early stages of synapse dismantling concomitant with diffuse localization of Dlg. Ecdysone is the major hormone that drives metamorphosis. Blockade of the ecdysone signaling specifically in presynaptic neurons by expression of a dominant-negative form of ecdysone receptors delayed presynaptic but not postsynaptic dismantling. However, inhibition of ecdysone signaling, as well as ubiquitination pathway or apoptosis specifically in postsynaptic muscles, arrested both presynaptic and postsynaptic dismantling. These results demonstrate that presynaptic and postsynaptic dismantling takes place through different mechanisms and that the postsynaptic side plays an instructive role in synapse dismantling.
突触重塑是一个广泛而基本的过程，它是神经元回路在发育过程中形成的基础，也是适应生理和/或环境变化的基础。然而，突触重塑的机制还不清楚。在果蝇幼虫的神经肌肉接点 (NMJ) 中，突触在变态过程中经历了剧烈而广泛的重塑，从而产生了具有成人特异性的突触。为了探索突触消除的分子和细胞过程，我们对果蝇变态早期 NMJ 突触进行了共聚焦显微镜、活体成像和电子显微镜 (EM) 观察，在此过程中，选择的基因的表达发生了遗传改变。我们报告说，在后突触支架蛋白 Disc large (Dlg) 的定位首先变得弥散，然后变得不可检测，因为幼虫肌肉经历了组织溶解，而突触前囊泡聚集并沿着轴突逆行运输，与 NMJ 细化过程中形成的丝状伪足结构同步，并与突触前质膜的回缩同步。EM 显示，在后突触亚基网膜在突触解体的早期阶段空泡化，同时 Dlg 弥散定位。蜕皮激素是驱动变态的主要激素。通过表达蜕皮激素受体的显性负形式特异性阻断突触前神经元中的蜕皮激素信号，延迟了突触前但不延迟突触后解体。然而，抑制蜕皮激素信号以及泛素化途径或凋亡特异性在突触后肌肉中，阻止了突触前和突触后解体。这些结果表明，突触前和突触后解体通过不同的机制发生，并且突触后侧在突触解体中起着指导作用。
