Brain Tumor Regulates Neuromuscular Synapse Growth and Endocytosis in Drosophila by Suppressing Mad Expression
Brain Tumor Regulates Neuromuscular Synapse Growth and Endocytosis in Drosophila by Suppressing Mad Expression
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DOI：
10.1523/jneurosci.0386-13.2013
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发表时间：
2013-07
期刊：
影响因子：
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通讯作者：
Wenwen Shi;Yan Chen;Guangming Gan;Dan Wang;Jinqi Ren;Qifu Wang;Zhiheng Xu;Wei Xie;Yong Q. Zha
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文献类型：
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作者：
Wenwen Shi;Yan Chen;Guangming Gan;Dan Wang;Jinqi Ren;Qifu Wang;Zhiheng Xu;Wei Xie;Yong Q. Zha
突触生长的精确调节对于功能神经回路的正确形成和可塑性至关重要。调节突触生长和功能的因素的识别和表征一直在深入研究中。在这里，我们报告脑肿瘤（brat）被认为是多种生物过程中的翻译抑制因子，在果蝇神经肌肉接头（NMJ）突触中发挥着至关重要的作用。免疫组织化学分析表明，与野生型相比，brat 突变体表现出突触过度生长，其特征是 NMJ 末端卫星过多，而电子显微镜显示突触小泡大小增加，但活性区密度降低。 brat 突变型 NMJ 的自发微型兴奋性连接电位振幅较大，诱发量子含量较低。与形态和生理表型一致，Brat 的缺失导致 NMJ 末端 FM1-43 的摄取减少，表明 brat 调节突触内吞作用。遗传分析表明，Brat 在突触上的作用是通过母亲介导的，以对抗十五肢麻痹 (Mad)，骨形态发生蛋白 (BMP) 信号通路的信号转导效应器。此外，生化分析显示，brat 突变体幼虫大脑中 Mad 蛋白水平上调，但 mRNA 水平正常，表明 Brat 抑制 Mad 翻译。一致地，在果蝇 S2 细胞中通过 RNA 干扰敲低 brat 也增加了 Mad 蛋白水平。这些结果共同揭示了 Brat 在通过抑制 BMP 信号转导介导的突触发育和内吞作用中发挥着重要且先前未被识别的作用。
The precise regulation of synaptic growth is critical for the proper formation and plasticity of functional neural circuits. Identification and characterization of factors that regulate synaptic growth and function have been under intensive investigation. Here we report that brain tumor (brat), which was identified as a translational repressor in multiple biological processes, plays a crucial role at Drosophila neuromuscular junction (NMJ) synapses. Immunohistochemical analysis demonstrated that brat mutants exhibited synaptic overgrowth characterized by excess satellite boutons at NMJ terminals, whereas electron microscopy revealed increased synaptic vesicle size but reduced density at active zones compared with wild-types. Spontaneous miniature excitatory junctional potential amplitudes were larger and evoked quantal content was lower at brat mutant NMJs. In agreement with the morphological and physiological phenotypes, loss of Brat resulted in reduced FM1-43 uptake at the NMJ terminals, indicating that brat regulates synaptic endocytosis. Genetic analysis revealed that the actions of Brat at synapses are mediated through mothers against decapentaplegic (Mad), the signal transduction effector of the bone morphogenetic protein (BMP) signaling pathway. Furthermore, biochemical analyses showed upregulated levels of Mad protein but normal mRNA levels in the larval brains of brat mutants, suggesting that Brat suppresses Mad translation. Consistently, knockdown of brat by RNA interference in Drosophila S2 cells also increased Mad protein level. These results together reveal an important and previously unidentified role for Brat in synaptic development and endocytosis mediated by suppression of BMP signaling.