NOTCH SIGNALING PATHWAY LIGANDS IN CARDIOVASCULAR DISEASE

(改编自申请人的摘要)识别导致人类心脏病的基因有助于深入了解心脏发育所涉及的分子途径。研究人员最近确定Jagged1(JAG1)是导致Alagille综合征的疾病基因，Alagille综合征是一种与心脏、肝脏和其他几种异常相关的遗传性疾病。JAG1是Notch信号通路中的一个配体，在许多生物中都显示参与了细胞命运的决定。Alagille综合征是一种显性疾病，在表型特征的表达上具有极大的变异性。一些携带JAG1突变的人只有一个临床特征，而不是Alagille综合征的多系统参与特征，这导致研究人员假设JAG1突变将在孤立心脏病患者中被发现。初步数据支持这一假设，因为研究人员已经确定了三名患有心脏病和JAG1突变的患者，他们没有表现出与Alagille综合征相关的肝脏异常。研究人员将把这项工作扩展到研究一组患者，以确定与心脏缺陷相关的JAG1突变的频率。为了了解JAG1是如何参与心血管发育的，研究人员将分析JAG1在发育中的小鼠胚胎中的表达位置和时间。研究人员还将探讨JAG1基因突变导致心脏病的机制。在果蝇中，Notch配体的突变导致截短蛋白，与Alagille综合征患者预测的类似，以显性负面方式起作用。然而，来自人类研究的令人信服的数据表明，JAG1作用的机制是单倍体不足。研究人员建议在小鼠胚胎中过度表达Alagille综合征患者中看到的突变，并确定它们对早期血管发育的影响。研究人员进一步提出，Notch信号通路的其他成员可能与心脏异常有关。Notch配体Delta最近被定位到6q27，这是基因组中一个与心脏病相关的区域，该区域缺失。研究人员将确定Delta是否是导致这些患者心脏病的基因。如果他们无法显示Delta的作用，他们将使用位置克隆方法从6q27开始识别与心脏病相关的其他基因(S)。综上所述，这项工作将加深对JAG1在心脏正常和异常发育中的作用的理解，并为发现更多与心脏疾病有关的基因奠定基础。

(Adapted from the Applicant's Abstract) Identification of genes causing human cardiac disease provides insight into the molecular pathways involved in heart development. The investigators have recently identified Jagged1 (JAG1) as the disease gene causing Alagille syndrome, a genetic disorder associated with heart, liver, and several other anomalies. JAG1 is a ligand in the Notch signaling pathway, shown in multiple organisms to be involved in cell fate determination. Alagille syndrome is a dominant disorder, with extreme variability in the expression of phenotypic features. Some individuals with JAG1 mutations have only a single clinical feature, rather than the multi- system involvement characteristic of Alagille syndrome, which led the investigators to hypothesize that JAG1 mutations would be identified in patients with isolated heart disease. The preliminary data support this hypothesis, as the investigators have identified three patients with cardiac disease and JAG1 mutations who do not manifest the liver abnormalities associated with Alagille syndrome. The investigators will extend this work to study a cohort of patients to determine the frequency of JAG1 mutations associated with cardiac defects. In order to understand how JAG1 is involved in cardiovascular development, the investigators will analyze location and timing of JAG1 expression in the developing mouse embryo. The investigators will also address the mechanism by which mutations in JAG1 cause heart disease. In Drosophila, mutations in Notch ligands which cause truncated proteins similar to those predicted in Alagille syndrome patients, act in a dominant negative fashion. However, there is compelling data from human studies that the mechanism for the effect of JAG1 is haploinsufficiency. The investigators propose to overexpress the mutations seen in Alagille syndrome patients in the mouse embryo and determine their effect on early vascular development. The investigators further propose that other members of the Notch signaling pathway may be associated with cardiac abnormalities. The Notch ligand Delta has recently been mapped to 6q27, a region of the genome associated with cardiac disease in patients deleted for this region. The investigators will determine if Delta is the gene responsible for heart disease in these patients. If they are unable to show a role for Delta, they will use a positional cloning approach to identify other gene(s) associated with cardiac disease from 6q27. In summary, this work will provide an increased understanding of the role of JAG1 in normal and abnormal development of the heart, and lay the foundation for identifying additional genes contributing to cardiac disease.