SIGNAL TRANSDUCTION PATHWAYS REGULATING NEURON DIFFERENTIATION

描述（由申请人提供）：拟议研究的长期目标是阐明哺乳动物大脑中调节神经元形态发生和连接的转录机制。我们最近发现，转录调节因子SnoN1在哺乳动物大脑的神经元定位控制中起着重要作用。RNAi对出生后大鼠幼鼠SnoN1基因的敲除可在体内强烈触发小脑皮层颗粒神经元的过度迁移。值得注意的是，SnoN1与转录因子FOXO1形成复合物，抑制x连锁无脑畸形基因双皮质素（DCX）的转录，从而控制小脑皮层中的神经元定位。重要的是，FOXO敲低表型和DCX敲低可抑制体内SnoN1敲低诱导的颗粒神经元过度迁移。有趣的是，SnoN1相关的选择性剪接异构体SnoN2在体内与SnoN1在foxo依赖性转录和神经元定位调控中的功能相反。这些发现将SnoN1- FOXO1复合物定义为一种协调神经元定位的新的细胞内在机制。我们的发现也提出了一些关于SnoN1-FOXO1复合物在控制神经元定位中的机制和生物学作用的基本问题。为了解决这些问题，我们提出验证一个假设，即特异性与SnoN1而非SnoN2相关的蛋白质在体内调节SnoN1- foxo1复合物的转录和神经元定位功能。除了DCX外，我们还将鉴定SnoN1-FOXO1复合体的新基因靶点，这些靶点介导SnoN1-FOXO1复合体控制神经元定位的能力。我们还将验证神经元定位的snon1调节与神经元发育的其他关键方面（包括神经元分支和树突发育）在体内协调的假设。最后，由于DCX控制大脑皮层中的神经元迁移，我们将使用体内RNAi和互补敲除方法来验证SnoN1通路的成分在体内调节大脑皮层中的神经元定位的假设。这项提议的研究代表了一系列重要的实验，这些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的发病机制中起着至关重要的作用，阐明控制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.