REGULATION OF NEURONAL DEVELOPMENT BY A NOVEL PHF6/PAF1 TRANSCRIPTIONAL PATHWAY

描述（由申请人提供）：智力残疾是一种普遍的发育障碍，影响了1-3%的人口。遗传学的进步已经导致许多智力残疾蛋白质的鉴定。然而，这些蛋白质如何调节大脑发育以及这些蛋白质突变导致智力残疾的机制仍然知之甚少。在过去的几年里，我们已经描述了特定的核x连锁智力残疾（XLID）蛋白在大脑发育中的功能。XLID蛋白PHF6的突变导致BFLS (BFLS)，其特征是智力迟缓和癫痫。我们发现PHF6的敲低严重损害了小鼠大脑皮层的神经元迁移。值得注意的是，PHF6与PAF1转录延伸复合体存在物理关联，抑制PAF1表型可以在体内复制PHF6敲低诱导的迁移表型。这些发现将PHF6和PAF1复合物定义为驱动大脑神经元迁移的新型转录途径的组成部分。我们的发现还提出了PHF6/PAF1转录通路在神经元迁移中的机制以及该通路在智力残疾中的病理生理相关性的基本问题。为了解决这些问题，我们将首先对小鼠大脑皮层神经元迁移中的PHF6进行结构-功能分析。我们将测试BFLS患者特异性PHF6突变对PHF6依赖性转录和神经元迁移的影响。我们还将验证PHF6在特定位点的磷酸化调节PHF6依赖性转录和神经元迁移的假设。在其他研究中，我们将验证PHF6调节神经元中活跃转录基因的转录延伸的假设，并确定驱动神经元迁移的PHF6靶点。最后，我们将确定皮层发育过程中PHF6/PAF1转录通路的解除对出生后小鼠白质异位和神经元兴奋性形成的影响。拟议的研究将促进我们对大脑中控制神经元定位的转录机制的理解，并导致对这些机制的解除管制如何有助于智力残疾的发病机制的见解。这些研究也有可能为BFLS和发育性认知障碍的新治疗方法奠定基础。

DESCRIPTION (provided by applicant): Intellectual disability is a prevalent developmental disorder, affecting 1-3% of the population. Advances in genetics have led to the identification of many intellectual disability proteins. However, how these proteins regulate brain development and the mechanisms by which mutations of these proteins cause intellectual disability remain poorly understood. During the past few years, we have characterized the functions of specific nuclear X-linked intellectual disability (XLID) proteins in brain development. Mutations of the XLID protein PHF6 cause the B¿rjeson-Forssman-Lehmannsyndrome (BFLS), which features intellectual delay and epilepsy. We have discovered that knockdown of PHF6 profoundly impairs neuronal migration in the mouse cerebral cortex in vivo. Remarkably, PHF6 physically associates with the PAF1 transcription elongation complex, and inhibition of PAF1 phenocopies the PHF6 knockdown-induced migration phenotype in vivo. These findings define PHF6 and the PAF1 complex as components of a novel transcriptional pathway that drives neuronal migration in the brain. Our findings have also raised fundamental questions on the mechanisms of the PHF6/PAF1 transcriptional pathway in neuronal migration and on the pathophysiological relevance of this pathway in intellectual disability. To address these questions, we will first perform structure- function analyses of PHF6 in neuronal migration in the mouse cerebral cortex. We will test the effect of BFLS patient-specific mutations of PHF6 on PHF6-dependent transcription and neuronal migration. We will also test the hypothesis that phosphorylation of PHF6 on specific sites regulates PHF6-dependent transcription and neuronal migration. In other studies, we will test the hypothesis that PHF6 regulates transcription elongation of actively transcribed genes in neurons and identify targets of PHF6 that drive neuronal migration. Finally, we will determine the effect of deregulation of the PHF6/PAF1 transcriptional pathway during cortical development on the formation of white matter heterotopias and neuronal excitability in postnatal mice. The proposed research will advance our understanding of the transcriptional mechanisms that govern neuronal positioning in the brain as well as lead to insights into how deregulation of these mechanisms contributes to the pathogenesis of intellectual disability. These studies also hold the potential of laying the foundation for novel therapeutic approaches to the treatment of BFLS and developmental cognitive disorders.