SIGNAL TRANSDUCTION PATHWAYS REGULATING NEURON DIFFERENTIATION

描述(申请人提供)：拟议研究的长期目标是阐明调控哺乳动物大脑中神经元形态发生和连接的转录机制。我们最近发现，转录调控因子SnoN1在哺乳动物大脑中控制神经元定位方面起着至关重要的作用。通过RNAi在出生后的大鼠幼鼠体内敲除SnoN1，强烈地触发了体内小脑皮质中颗粒神经元的过度迁移。值得注意的是，SnoN1与转录因子FOXO1形成复合体，抑制X连锁无脑基因Doublecortin(DCX)的转录，从而控制小脑皮质中神经元的定位。重要的是，FOXO基因敲除表型和DCX基因敲除抑制了SnoN1基因敲除诱导的颗粒神经元在体内的过度迁移。有趣的是，SnoN1相关的选择性剪接异构体SnoN2反对SnoN1在体内调节FOXO依赖的转录和神经元定位的功能。这些发现将SnoN1-FOXO1复合体定义为一种协调神经元定位的新的细胞内在机制。我们的发现也对SnoN1-FOXO1复合体在控制神经元定位方面的机制和生物学作用提出了几个基本问题。为了解决这些问题，我们建议测试这一假设，即与SnoN1特异相关但不与SnoN1相关的蛋白质调节SnoN1-FOXO1复合体在体内转录和神经元定位的功能。我们还将确定SnoN1-FOXO1复合体的新基因靶点，除了DCX，它还介导SnoN1-FOXO1复合体控制神经元定位的能力。我们还将测试这一假设，即SnoN1对神经元定位的调节与神经元发育的其他关键方面是协调的，包括体内神经元分支和树突发育。最后，由于DCX控制着大脑皮层中的神经元迁移，我们将在体内使用RNAi和互补的基因敲除方法来验证SnoN1通路的组件在体内调节大脑皮层中神经元定位的假设。这项拟议的研究代表了一系列重要的实验，将促进我们对控制大脑中神经元定位的机制的理解。由于神经元定位障碍在遗传性智力低下和癫痫障碍的发病机制中起着关键作用，阐明神经元定位的机制也将有助于更好地理解这些认知和癫痫的神经发育障碍。

DESCRIPTION (provided by applicant): The long-term goals of the proposed research are to elucidate the transcriptional mechanisms regulating neuronal morphogenesis and connectivity in the mammalian brain. We recently discovered that the transcriptional regulator SnoN1 plays an essential role in the control of neuronal positioning in the mammalian brain. Knockdown of SnoN1 by RNAi in postnatal rat pups robustly triggers the excessive migration of granule neurons in the cerebellar cortex in vivo. Remarkably, SnoN1 forms a complex with the transcription factor FOXO1 that represses transcription of the X-linked lissencephaly gene doublecortin (DCX) and thereby controls neuronal positioning in the cerebellar cortex. Importantly, FOXO knockdown phenocopies and DCX knockdown suppresses the SnoN1 knockdown-induced excessive migration of granule neurons in vivo. Interestingly, the SnoN1-related alternatively spliced isoform, SnoN2, opposes the function of SnoN1 in the regulation of FOXO-dependent transcription and neuronal positioning in vivo. These findings define the SnoN1- FOXO1 complex as a novel cell-intrinsic mechanism that orchestrates neuronal positioning. Our findings have also raised several fundamental questions on the mechanisms and biological role of the SnoN1-FOXO1 complex in the control of neuronal positioning. To address these questions, we propose to test the hypothesis that proteins that specifically associate with SnoN1 but not SnoN2 regulate the functions of the SnoN1-FOXO1 complex in transcription and neuronal positioning in vivo. We will also identify novel gene targets of the SnoN1- FOXO1 complex, besides DCX, that mediate the ability of the SnoN1-FOXO1 complex to control neuronal positioning. We will also test the hypothesis that SnoN1-regulation of neuronal positioning is coordinated with other key aspects of neuronal development including neuronal branching and dendrite development in vivo. Finally, because DCX controls neuronal migration in the cerebral cortex, we will use in vivo RNAi and a complementary knockout approach to test the hypothesis that components of the SnoN1 pathway regulate neuronal positioning in the cerebral cortex in vivo. The proposed research represents an important set of experiments that will advance our understanding of the mechanisms that control neuronal positioning in the brain. Since disturbances of neuronal positioning play a critical role in the pathogenesis of inherited mental retardation and epilepsy disorders, elucidating the mechanisms that govern neuronal positioning should also lead to a better understanding of these neurodevelopmental disorders of cognition and epilepsy.