Department of Neuroscience, United States; Stem Cell Institute, United States.
Neurosci Lett. 2010 Apr 19;474(1):46-51. doi: 10.1016/j.neulet.2010.03.004. Epub 2010 Mar 7.
During neural development, members of MTG family of transcriptional repressors are induced by proneural basic helix-loop-helix (bHLH) transcription factors and in turn inhibit the activity of the bHLH proteins, forming a negative feedback loop that regulates the normal progression of neurogenesis. Three MTG genes, MTG8, MTG16 and MTGR1, are expressed in distinct patterns in the developing nervous system. Various bHLH proteins are also expressed in distinct patterns. We asked whether there is a functional relationship between specific MTG and bHLH proteins in developing chick spinal cord. First, we examined if each MTG gene is induced by specific bHLH proteins. Although expression of NEUROG2, ASCL1 and MTG genes overlapped, the boundaries of gene expression did not match. Ectopic expression analysis showed that MTGR1 and NEUROD4, which show similar expression patterns, are regulated differently by NEUROG2 and ASCL1. Thus, our results show that expression of MTG genes is not regulated by a single upstream bHLH protein, but represents an integration of the activity of multiple regulators. Next, we asked if each MTG protein inhibits specific bHLH proteins. Transcription assay showed that NEUROG2 and ASCL1 are inhibited by MTGR1 and MTG16, and less efficiently by MTG8. Deletion mapping of MTGR1 showed that MTGR1 binds NEUROG2 and ASCL1 using multiple interaction surfaces, and all conserved domains are required for its repressor activity. These results support the model that MTG proteins form a higher-order repressor complex and modulate transcriptional activity of bHLH proteins during neurogenesis.
在神经发育过程中，MTG 家族的转录抑制因子被神经前体细胞碱性螺旋-环-螺旋（bHLH）转录因子诱导，反过来又抑制 bHLH 蛋白的活性，形成一个负反馈环，调节神经发生的正常进程。三个 MTG 基因，MTG8、MTG16 和 MTGR1，在发育中的神经系统中以不同的模式表达。各种 bHLH 蛋白也以不同的模式表达。我们想知道在发育中的鸡脊髓中，特定的 MTG 和 bHLH 蛋白之间是否存在功能关系。首先，我们检查了每个 MTG 基因是否被特定的 bHLH 蛋白诱导。虽然 NEUROG2、ASCL1 和 MTG 基因的表达重叠，但基因表达的边界并不匹配。异位表达分析表明，表达模式相似的 MTGR1 和 NEUROD4 受 NEUROG2 和 ASCL1 的调控方式不同。因此，我们的结果表明，MTG 基因的表达不是由单个上游 bHLH 蛋白调节的，而是代表了多个调节因子活性的整合。接下来，我们询问每个 MTG 蛋白是否抑制特定的 bHLH 蛋白。转录分析表明，NEUROG2 和 ASCL1 被 MTGR1 和 MTG16 抑制，而被 MTG8 抑制的程度较低。MTGR1 的缺失作图表明，MTGR1 使用多个相互作用表面结合 NEUROG2 和 ASCL1，并且所有保守结构域都需要其抑制活性。这些结果支持这样的模型，即 MTG 蛋白形成一个更高阶的抑制复合物，并在神经发生过程中调节 bHLH 蛋白的转录活性。
