Novel candidate mechanisms of fragile X syndrome

脆性X染色体综合征（FXS）是最常见的遗传形式的智力迟钝，由破坏FMR1基因的突变引起。很大一部分FXS患者具有自闭症谱系障碍（ASD）的特征。FMR1编码的蛋白是脆性X智力迟钝蛋白（FMRP），它结合mrna并调节其翻译。FMRP靶mrna在人类神经发育中的身份和功能以及它们如何促进FXS尚不清楚。在我的初步数据中，其中部分数据构成了我目前出版的手稿的基础（Kwan etal ., Cell, 2012），我表明，在发育中的人类新皮层中，一氧化氮合酶1 (NOS1) mRNA与FMRP结合并受其调节，而在胎儿FXS病例中，NOS1蛋白丢失。因此，NOS1功能丧失是FXS的一种新的候选机制。在本申请中，我建议进一步研究这一令人兴奋的研究方向。在Aim 1中，我将研究NOS1的缺失如何促进FXS和ASD的病理生理，FXS通常与ASD共病。具体来说，我将分析：锥体NOS1在发育过程中的神经生物学作用；NOS1的遗传贡献以及NOS1上游参与一氧化氮合成的基因对ASD的影响；以及锥体神经元中NOS1信号的下游事件。对于Aim 2，我建议使用死后的人类脑组织来确定FXS的其他新的候选机制，并使用FXS大脑和神经干细胞来测试它们在FXS中的失调。这种多方面的应用有望在几个领域提供培训，包括人类遗传学，生物化学，人体组织处理，突触分析，神经干细胞培养和高通量测序的新技术。这种额外的训练对我成功过渡到独立至关重要。在导师阶段，我的培训进展和我寻找独立职位的过程将由我的共同导师和另外四名具有不同专业知识的教员组成的委员会监督。本研究对当前FXS的研究方法具有启示意义，并有可能揭示FXS和ASD的新分子途径。

DESCRIPTION (provided by applicant): Project Summary Fragile X syndrome (FXS), the most common inherited form of mental retardation, result from mutations that disrupt the FMR1 gene. A large proportion of FXS patients have features of autism spectrum disorder (ASD). The protein encoded by FMR1, fragile X mental retardation protein (FMRP), binds mRNAs and regulates their translation. The identity and function of FMRP target mRNAs in human neurodevelopment and how they contribute to FXS are not well understood. In my preliminary data, parts of which formed the basis of my manuscript currently in press (Kwan et al., Cell, 2012), I show that nitric oxide synthase 1 (NOS1) mRNA is bound to and regulated by FMRP in the developing human neocortex and NOS1 protein is lost in fetal cases of FXS. Therefore, NOS1 loss of function represents a promising novel candidate mechanism of FXS. In this application, I propose to further pursue this exciting line of research. In Aim 1, I will examine how loss of NOS1 may contribute to the pathophysiology of FXS and ASD, with which FXS is often comorbid. Specifically, I will analyze: the neurobiological role of pyramidal NOS1 during development; the genetic contribution of NOS1, and genes that act upstream of NOS1 in the synthesis of nitric oxide (NO), to ASD; and the events downstream of NOS1 signaling in pyramidal neurons. For Aim 2, I propose to identify additional novel candidate mechanisms of FXS using postmortem human brain tissue and to test their dysregulation in FXS using FXS brains and neural stem cells. This multifaceted application is expected to provide training in several areas, including novel techniques in human genetics, biochemistry, human tissue processing, synapse analysis, neural stem cell culture, and high-throughput sequencing. This additional training is critical to my successful transition to independence. The progress of my training during the mentored phase and my search for an independent position will be overseen by my co-mentors and a committee of four additional faculty members with diverse expertise. The proposed studies have implications for current approaches to study of FXS and have the potential to uncover novel molecular pathways of not only FXS but also ASD. PUBLIC HEALTH RELEVANCE: Project Narrative Fragile X syndrome is the most common inherited form of mental retardation. I propose to study the molecular underpinnings of fragile X syndrome. This work will have implications for potential therapies for fragile X syndrome, as well as autism spectrum disorder.