HELIX-LOOP-HELIX PROTEINS AND VERTEBRATE NEUROGENESIS

遗传学和分子生物学研究表明，碱性-螺旋-环-螺旋转录因子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。这些蛋白包括MASH1、XASH3和NeuroD/Math/Neurogenin家族的成员。在非洲爪哇胚胎中，强制表达单一的bHLH转录因子(例如，NeuroD1)可以启动神经元分化，即使是在通常不会成为神经元的细胞中也是如此。在小鼠身上，这些基因中的几个有针对性的突变已经表明，它们对于神经元亚群的形成是必不可少的。然而，神经bHLH蛋白启动神经元形成或分化的分子机制大多仍不清楚。为了进一步了解神经bHLH的功能，我们建议：1)鉴定和鉴定神经元形成所必需的神经bHLH蛋白的结构域；2)表征不同的神经bHLH蛋白对特定靶基因的激活作用；3)分析Notch和ras信号通路对神经bHLH蛋白功能的抑制作用。这些研究将通过我们最近开发的哺乳动物细胞培养模型来促进。在该系统中，单个神经bHLHc DNA的转染足以指导多潜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控哺乳动物(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失去的神经元的策略。

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.