Molecular and Developmental Analysis of Holoprosencephaly

描述（由申请人提供）：前脑无裂畸形（HPE）是一种常见的人类发育缺陷，由前脑和/或面中部中线无法确定引起。HPE与NODAL和Sonic hedgehog（SHH）通路组分中的杂合突变相关，但临床表现高度可变，许多突变携带者不受影响。因此，人们认为，这种突变必须与更常见的修饰，遗传和/或环境相互作用。此外，对于个体HPE相关基因，观察到许多不同的变异等位基因。因此，HPE的特征在于缺乏明确的基因型-表型相关性和高遗传异质性。这些现象阻碍了对HPE病因学的深入了解，并且难以为突变携带者提供咨询。为了提供准确的信息，需要解决两个重要问题：1）必须从机制上识别和理解真正的致病性突变与分级突变率和表达率的修饰因子之间的相互作用; 2）必须分析特定的HPE相关遗传变异，以证明它们在功能上存在缺陷，并识别潜在的机制。这项建议涉及这两个问题。我们在小鼠中建立了HPE模型。CDON编码一种多功能辅助受体，可通过多种途径促进信号传导，包括SHH途径。具有Cdon突变的小鼠在SHH信号传导中具有很大程度上的阈下缺陷。这些小鼠对由本身不足以产生HPE的遗传或环境修饰剂诱导的一系列颅面和前脑HPE表型敏感。在这些修饰符是短暂的胎儿酒精暴露在原肠胚形成。新的发现表明，除了在SHH信号传导中的作用外， CDON与NODAL受体复合物的组分相互作用。此外，NODAL通路活性的瞬时抑制似乎是CDON丢失和胎儿酒精暴露之间协同相互作用的点。NODAL信号的调节代表了CDON的新作用，补充了其在面部和前脑中线图案形成期间SHH信号的功能。我们还鉴定和表征了人类HPE中功能丧失的CDON突变。SHH受体复合物的其他组分也在人类HPE中突变，包括PTCH 1和BOC，但关于这些受体变体是否以及如何在SHH信号传导中有缺陷的信息很少。提出了以下目的：1）确定CDON和NODAL途径之间的遗传和机制相互作用;和2）确定BOC和PTCH 1中HPE相关变体的功能和机制后果。成功完成拟议目标将提供以下重要信息：1）环境因素如何与诱发突变相互作用，从而为预防行动提供基础; 2）特定患者突变的致病性。因此，这些研究有望帮助其后代可能遗传上易患HPE的个体进行咨询。

DESCRIPTION (provided by applicant): Holoprosencephaly (HPE) is a common human developmental defect caused by failure to define the midline of the forebrain and/or midface. HPE is associated with heterozygous mutations in NODAL and Sonic hedgehog (SHH) pathway components, but clinical presentation is highly variable, and many mutation carriers are unaffected. It is therefore thought that such mutations must interact with more common modifiers, genetic and/or environmental. Furthermore, many distinct variant alleles are observed for individual HPE-associated genes. HPE is therefore characterized by a lack of clear genotype-phenotype correlation and by high genetic heterogeneity. These phenomena have prevented a deep understanding of HPE etiology and made it difficult to provide counseling to mutation carriers. Two significant issues need to be addressed to provide accurate information: 1) interactions between bona fide pathogenic mutations and the modifiers that grade penetrance and expressivity must be identified and understood mechanistically; and 2) specific HPE-associated genetic variants must be analyzed to prove that they are functionally deficient and identify the underlying mechanism. This proposal addresses both issues. We have modeled HPE in mice. CDON encodes a multifunctional coreceptor that promotes signaling by several pathways, including the SHH pathway. Mice with a mutation in Cdon have a largely subthreshold defect in SHH signaling. These mice are sensitive to induction of a spectrum of craniofacial and forebrain HPE phenotypes by genetic or environmental modifiers that are, themselves, insufficient to produce HPE. Among these modifiers is transient fetal alcohol exposure during gastrulation. New findings indicate that, in addition to its role in SHH signaling, CDON interacts with components of the NODAL receptor complex. Furthermore, transient inhibition of NODAL pathway activity appears to be the point of synergistic interaction between loss of CDON and fetal alcohol exposure. Regulation of NODAL signaling represents a new role for CDON, complementing its function in SHH signaling during midline patterning of the face and forebrain. We have also identified and characterized loss-of-function CDON mutations in human HPE. Other components of the SHH receptor complex are also mutated in human HPE, including PTCH1 and BOC, but there is little information on whether and how these receptor variants are defective in SHH signaling. The following Aims are proposed: 1) to determine genetic and mechanistic interactions between CDON and the NODAL pathway; and 2) to determine the functional and mechanistic consequences of HPE-associated variants in BOC and PTCH1. The successful completion of the proposed aims will provide important information about: 1) how environmental factors interact with predisposing mutations, thus providing a basis for preventive action; and 2) the pathogenic nature of specific patient mutations. Therefore, these studies are expected to aid in the counseling of individuals whose offspring may be genetically predisposed to HPE.