Mice That Lack CDO: A Model for Mild Holoprosencephaly

描述（由申请人提供）：这项高风险/高影响研究提案的目的是利用本实验室开发的Cdo“敲除”小鼠作为轻度形式的前脑全畸形（HPE）的模型，HPE是一种影响颅面和前脑发育的人类出生缺陷。Sonic hedgehog基因（Shh）单倍性不足是家族性和散发性HPE最常见的原因。Shh突变携带者的表型可以是高度可变的，即使在一个谱系中，颅面畸形范围从独眼和长鼻到鼻中隔缺失和单独的上颌中门牙。尽管我们对Shh信号是如何被靶细胞转导的了解很多，但在颅面发育过程中，这一途径所调节的基因却很少被发现。Cdo和Boc编码促进骨骼肌前体细胞分化的细胞表面受体的共组分。这两个基因也在HPE影响的面部结构发育中表达。我们已经破坏了小鼠胚胎干细胞中的Cdo基因，并将这种突变引入种系。缺乏CDO的小鼠在颅面发育中表现出高度渗透性缺陷，这与在人类轻度HPE中观察到的缺陷惊人地相似，包括缺乏或孤立的中央上颌门牙，鼻中隔软骨缺乏或发育不全。对于轻度HPE面部异常的发展，提出了一个基于Shh信号与Cdo和/或Boc表达之间因果关系的假设：发育中的额鼻突和上颌突外胚层产生的Shh诱导相邻间质中Cdo和/或Boc的表达。该区域细胞的确定、分化或存活需要CDO/BOC受体的后续活动，最终形成特定的中面结构。据预测，sh介导的Cdo和/或Boc表达的破坏导致轻度HPE特征的面部异常。这项提议的具体目的是用胚胎学、遗传学和细胞生物学的结合方法来检验这一假设。如果这一假设被证明是正确的，这笔拨款将对细胞信号传导领域产生巨大的创新价值，并可能导致最终用于诊断、预防或治疗轻度HPE的分子靶点的鉴定。

DESCRIPTION (provided by applicant): The objective of this high risk/high impact research proposal is to exploit the Cdo "knockout" mouse developed in this lab as a model for mild forms of holoprosencephaly (HPE), a human birth defect that affects craniofacial and forebrain development. Haploinsufficiency for Sonic hedgehog (Shh) is the most common known cause of both familial and sporadic HPE. The phenotype of Shh mutation carriers can be highly variable, even within a single pedigree, with craniofacial malformations ranging from cyclopia and a proboscis to absence of the nasal septum and a solitary median maxillary incisor. Although much is known about how Shh signals are transduced by target cells, few of the genes that this pathway regulates during craniofacial development have been identified. Cdo and Boc encode co-components of a cell surface receptor that promotes differentiation of skeletal muscle precursor cells. Both genes are also expressed in developing facial structures affected in HPE. We have disrupted the Cdo gene in mouse ES cells and introduced this mutation into the germline. Mice lacking CDO display highly penetrant defects in craniofacial development that are strikingly similar to those observed in milder forms of HPE in humans, including lack of, or solitary central, maxillary incisors, and lack or hypoplasia of the cartilage of the nasal septum. A hypothesis based on a causal relationship between Shh signaling and Cdo and/or Boc expression is proposed for the development of facial anomalies in mild form HPE: Shh produced by the ectoderm of the developing frontonasal and maxillary processes induces the expression of Cdo and/or Boc in the adjacent mesenchyme. Subsequent activities of the CDO/BOC receptor are required for the determination, differentiation or survival of cells in this region, ultimately resulting in formation of specific midface structures. It is predicted that disruption of Shh-mediated expression of Cdo and/or Boc results in facial anomalies characteristic of mild HPE. The specific aim of this proposal is to test this hypothesis with a combined embryological, genetic and cell biological approach. If the hypothesis is proven correct, the impact of this grant will be of great innovative value for the cell-signaling field and may lead to identification of molecular targets ultimately used for the diagnosis, prevention or treatment of mild HPE.