Characterization of Autism Susceptibility Genes on Chromosome 15q11-13

描述(由申请人提供)： 15q11-13染色体母系重复是导致自闭症谱系障碍(ASD)的最常见的拷贝数变异，在所有ASD病例中存在1-3%。重要的是，父亲的复制不会导致自闭症，这表明致病基因(S)是印记的。在染色体区域的40个基因中，只有UBE3A在大脑中的母体染色体中唯一表达。UBE3A是Angleman综合征(AS)基因，是一种E3泛素连接酶突变，会导致智力低下、言语障碍、过度社交行为、过度大笑、癫痫发作和刻板印象的面部特征。鉴于该基因在导致这种严重精神障碍中的作用，以及最近的证据表明泛素途径在ASD病理生理学中的作用，我们假设Ube3a在15q11-13重复中介导了ASD的风险。为了研究UBE3A在脑中的功能，我们获得了UBE3A母系(基因敲除)小鼠，并产生了携带两个额外UBE3A副本的新小鼠，模拟了ASD高发的等着丝粒15q紊乱。重要的是，我们已经证明了这种idic15小鼠模型显示了大脑蛋白质泛素化的显著增加。根据观察到的AS(15q11-13缺失)和ASD(15q11-13重复)的相反症状，如婴儿期高张力与低张力，以及儿童早期高社交行为与低社交行为，我们预测缺乏Ube3a和过度表达Ube3a的小鼠将表现出相反的表型，这将突出UBE3A的正常功能。目前的建议的目标如下：1)证明UBE3A在从母亲那里遗传额外15q11-13拷贝的儿童中观察到的ASD的贡献，以及2)阐明这些疾病的细胞学基础和UBE3A在神经元回路功能中的作用。为了实现这一目标，我们将首先在我们的新型过度表达小鼠中表征与ASD(社交互动、婴儿发声)和神经精神疾病(例如，焦虑)直接相关的行为。其次，丘脑神经元表达高水平的Ube3a，在ASD中表现出代谢活动(FDG摄取)降低，并可能导致行为缺陷。因此，我们将对UBE3A过度表达和缺陷小鼠的丘脑电路结构和功能进行全面的电生理学表征。总体而言，我们预测过量的UBE3A将足以复制15q11-13ASD的许多特征，定义一种新的ASD遗传模式。 公共卫生相关性： 导致自闭症的最常见的染色体异常是15q11-13号染色体的重复，这会导致孩子有太多的几个基因副本。我们将把一个可能在15q重复中起重要作用的基因的额外拷贝插入小鼠体内，描述小鼠的行为，并在分子水平上调查这些基因如何导致与自闭症相关的异常行为。

DESCRIPTION (provided by applicant): Maternal duplication of chromosome 15q11-13 is the most common copy number variation causing autism spectrum disorder (ASD), present in 1-3% of all ASD cases. Importantly, paternal duplication does not cause ASD, suggesting that the causative gene(s) are imprinted. Of 40 genes in the chromosomal region, only UBE3A is expressed exclusively from the maternal chromosome in the brain. UBE3A, Angleman's syndrome (AS) gene, is an E3 ubiquitin ligase mutated to cause mental retardation, impaired speech, overly-social behavior, excess laughing, seizures and stereotyped facial features. Given the gene's role in causing this severe mental disorder, and the recent evidence implicating ubiquitin pathways in ASD pathophysiology, we hypothesize that Ube3a mediates ASD risk in 15q11-13 duplication. In order to study UBE3A function in brain, we obtained UBE3A maternal-deificent (knockout) mice, and generated novel mice harboring two extra copies of UBE3A, modeling isodicentric 15q disorder which shows a high prevalence of ASD. Importantly, we have shown that this idic15 mouse model displays a marked increase of brain protein ubiquitination. Based on the observed opposing symptoms of AS (15q11-13 deletion) and ASD (15q11-13 duplication), such as hyper- tonia vs hypo-tonia in infancy and hyper-social behavior vs. hypo-social behavior in early childhood, respectively, we predict that mice lacking Ube3a and overexpressing Ube3a will show opposing phenotypes which will highlight the normal function of UBE3A. The objectives of the current proposal are the following: 1) to demonstrate that UBE3A contributes to the ASD observed in children inheriting extra copies of 15q11-13 from their mother, and 2) to elucidate the cellular basis of these disorders and UBE3A function in neuronal circuit function. Towards this goal, we will first characterize behaviors directly relevant to ASD (social interaction, infant vocalization) and to neuropsychiatric disease (e.g., anxiety) in our novel overexpressing mice. Second, thalamic neurons express high levels of Ube3a, display reduced metabolic activity (FDG uptake) in ASD, and could underlie behavioral defects. Therefore, we will perform a comprehensive electrophysiology-based characterization of thalamic circuitry structure and function in both UBE3A overexpressing and deficent mice. Overall, we predict excess UBE3A will be sufficent to replicate many of the features of 15q11-13 ASD, defining a new genetic model of ASD. PUBLIC HEALTH RELEVANCE: The most common chromosomal abnormality that causes autism is duplication of chromosome 15q11- 13, which results in a child having too many copies of several genes. We will insert extra copies of a gene likely to be important in 15q duplication into mice, characterize the behavior of the mice, and investigate, on a molecular level, how these genes might lead to abnormal behaviors related to autism.