An Animal Model for Cornelia de Lange Syndrome

描述(申请人提供)：Cornelia de Lange综合征(CDLS)是由控制姐妹染色单体凝聚力的基因突变引起的。CDLS患者表现为出生前和出生后发育缓慢、智力低下、自闭症特征和四肢和器官结构异常。出乎意料的是，模式生物研究表明，不同的CDLS缺陷是由控制发育的基因表达的影响造成的，而不是染色单体凝聚力的缺陷。这项建议的长期目标是了解凝聚力因素如何调节基因表达和发育，以增加对CDLS和相关出生缺陷的病因的理解。粘附素复合体具有环状结构，其主导思想是粘附素通过包围姐妹染色单体来调节凝聚力。NIPBL(NIPB-like)蛋白将粘附素加载到染色体上，大多数CDLS患者具有杂合性功能丧失NIPBL突变。这些突变使NIPBL减少了不到30%，并且不会造成内聚力缺陷。一小部分较轻的CDLS病例是由粘附素亚基的错义突变引起的。这些突变也不会影响凝聚力。CDLS最令人费解的方面是，凝聚力因素的如此微小变化如何对发展产生如此巨大的影响。在模式生物中，类似的微小变化会改变基因的表达和发育，而不会改变凝聚力。在果蝇中，粘附素优先与活性基因结合，细胞系之间结合的差异与基因转录的差异有关。这些数据表明了一种模型，在该模型中，粘附素包围了转录解开染色体的活性基因。进一步提出粘附素通过多种机制影响转录。由于粘附素结合得如此紧密，它与基因的关联必须由NIPBL动态控制，以促进转录。因此，CDLS被认为是由改变基因表达的粘附素动态变化引起的。人和果蝇的凝聚力因子在结构和功能上有很强的相似性。这项拟议的工作将利用高度顺从的果蝇动物模型来阐明凝聚力因素如何调节基因表达。有三个目的：(1)确定凝聚力因子如何影响细胞和体内的转录延伸、基因激活和绝缘体功能；(2)通过染色质免疫沉淀确定基因表达如何调节粘附素结合；(3)通过光漂白后的荧光恢复确定凝聚力因子的变化如何影响体内粘附素染色体结合动力学。希望这些研究的洞察力将有助于阐明凝聚力因素的微小变化导致CDL的机制，并影响诊断和治疗方法的发展。与公众健康相关这个项目是为了确定当细胞分裂时控制染色体正确分裂的蛋白质如何控制基因和果蝇的发育。这些蛋白质的人类版本的变化会导致Cornelia de Lange综合征(CDLS)，这是一种严重的发育障碍。CDLS儿童出生前后发育缓慢，患有智力低下和四肢及心脏等器官的缺陷；通过研究这些蛋白质在果蝇中的作用，我们将获得有助于寻找新的方法来诊断和治疗CDLS患者的知识。

DESCRIPTION (provided by applicant): Cornelia de Lange syndrome (CdLS) is caused by mutations in genes that control sister chromatid cohesion. CdLS patients show slow pre- and postnatal growth, mental retardation, autistic features and structural abnormalities in limbs and organs. Unexpectedly, model organism studies indicate that the diverse CdLS deficits are caused by effects on expression of genes that control development, rather than defects in chromatid cohesion. The long-term goal of this proposal is to learn how cohesion factors regulate gene expression and development to increase understanding of the etiology of CdLS and related birth defects. The cohesin complex has a ring-like structure and the leading idea is that cohesin mediates cohesion by encircling the sister chromatids. The NIPBL (Nipped-B-Like) protein loads cohesin onto chromosomes, and most CdLS patients have heterozygous loss-of-function NIPBL mutations. These mutations reduce NIPBL by less than 30%, and do not cause cohesion defects. A small fraction of milder CdLS cases are caused by missense mutations in cohesin subunits. These mutations also do not affect cohesion. The most puzzling aspect of CdLS is how such small changes in cohesion factors have such dramatic effects on development. In model organisms, similar small changes alter gene expression and development without altering cohesion. In Drosophila, cohesin binds preferentially to active genes, and differences in binding between cell lines correlate with differences in gene transcription. These data suggest a model in which cohesin encircles active genes where transcription unwinds the chromosome. It is further proposed that cohesin affects transcription by multiple mechanisms. Because cohesin binds so tightly, its association with genes must be controlled dynamically by NIPBL to facilitate transcription. Thus it is proposed that CdLS is caused by changes in cohesin dynamics that alter gene expression. There are strong structural and functional parallels between human and Drosophila cohesion factors. The proposed work will take advantage of the highly amenable Drosophila animal model to elucidate how cohesion factors regulate gene expression. There are three aims: (1) determine how cohesion factors affect transcriptional elongation, gene activation, and insulator function in cells and in vivo, (2) determine how gene expression regulates cohesin binding using chromatin immunoprecipitation, and (3) determine how changes in cohesion factors affect cohesin chromosome-binding dynamics in vivo using fluorescence recovery after photobleaching. It is hoped that insights from these studies will shed light on the mechanisms by which small changes in cohesion factors cause CdLS, and impact the development of diagnostic and therapeutic methods. PUBLIC HEALTH RELEVANCE This project is to determine how proteins that control the proper division of chromosomes when cells divide also control genes and development in the fruitfly. Changes in the human versions of these proteins cause Cornelia de Lange syndrome (CdLS), a severe developmental disorder. CdLS children display slow growth before and after birth, and are afflicted with mental retardation and defects in limbs and organs such as the heart; by examining how these proteins work in the fruitfly, we will gain knowledge that will aid the search for new methods to diagnose and treat CdLS patients.