HELIX-LOOP-HELIX PROTEINS AND VERTEBRATE NEUROGENESIS

遗传和分子研究表明，转录因子碱性螺旋环螺旋 (bHLH) 家族的蛋白质是脊椎动物神经前体形成和神经元分化的关键调节因子。 这些蛋白质包括 MASH1、XASH3 以及 NeuroD/MATH/neurogenin 家族的成员。 在非洲爪蟾胚胎中，单个 bHLH 转录因子（例如 NeuroD1）的强制表达可以启动神经元分化，即使在通常不会成为神经元的细胞中也是如此。 在小鼠中，其中几个基因的靶向突变表明它们对于神经元亚群的形成至关重要。然而，神经 bHLH 蛋白启动神经元形成或分化的分子机制仍然未知。为了进一步了解神经 bHLH 功能，我们建议：1）识别和表征神经元形成所需的神经 bHLH 蛋白的结构域，2）表征不同神经 bHLH 蛋白对特定靶基因的激活，3）分析 Notch 和 ras 信号通路对神经 bHLH 蛋白功能的抑制。我们最近开发的哺乳动物细胞培养模型将促进这些研究。 在该系统中，转染单个神经 bHLH cDNA 足以指导多能细胞系的神经元形成。这项工作应该有助于更好地理解调节哺乳动物（包括人类）正常神经发生和神经元分化的机制。 从长远来看，这些信息可能有助于制定替代因损伤或神经退行性疾病而丢失的神经元的策略。

Genetic and molecular studies have shown that proteins from the basic-helix-loop-helix (bHLH) family of transcription factors are key regulators of neural precursor formation and neuronal differentiation in vertebrates. These proteins include MASH1, XASH3, and members of the neuroD/MATH/neurogenin families. In Xenopus embryos, forced expression of a single bHLH transcription factor (e.g. neuroD1) can initiate neuronal differentiation, even in cells which are normally not destined to become neurons. In mice, targeted mutations in several of these genes have shown that they are essential for the formation of subsets of neurons. However, the molecular mechanisms by which the neural bHLH proteins function to initiate neuron formation or differentiation remain mostly unknown. To further our understanding of neural bHLH function, we propose to: 1) identify and characterize the domains of the neural bHLH proteins that are necessary for the formation of neurons, 2) characterize the activation of specific target genes by different neural bHLH proteins, and 3) analyze the inhibition of neural bHLH protein function by the Notch and ras signaling pathways. These studies will be facilitated by a mammalian cell culture model that we recently have developed. In this system, transfection of a single neural bHLH cDNA is sufficient to direct neuron formation from a multipotential cell line. This work should lead to a better understanding of the mechanisms that regulate normal neurogenesis and neuronal differentiation in mammals, including humans. In the long term, such information may contribute to developing strategies for replacement of neurons lost due to injury or neurodegenerative diseases.