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标是利用本实验室开发的CDO“基因敲除”小鼠作为轻度无前脑畸形(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(Shh)的单倍体功能不全是家族性和散发性HPE最常见的已知原因。Shh突变携带者的表型差异很大，即使在一个家系内也是如此，有颅面畸形，从睫状突和鼻状突到没有鼻中隔和孤立的上颌正中切牙。虽然对Shh信号如何被靶细胞转导有很多了解，但在颅面发育过程中这一途径调节的基因还很少被识别。CDO和Boc编码细胞表面受体的共同成分，促进骨骼肌前体细胞的分化。这两个基因也在HPE的面部结构发育中表达。我们已经破坏了小鼠ES细胞中的CDO基因，并将这种突变引入了生殖系。缺乏CDO的小鼠在头面部发育中表现出高度穿透性的缺陷，与人类轻度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，以及鼻中隔软骨缺乏或发育不良。基于Shh信号与CDO和/或Boc表达之间的因果关系，提出了一种假说，认为面部轻度畸形的发生与HPE有关：发育中的额鼻和上颌突外胚层产生Shh，诱导相邻间充质中CDO和/或Boc的表达。CDO/BOC受体的后续活动是该区域细胞的决定、分化或生存所必需的，最终导致特定的面中部结构的形成。据预测，Shh介导的CDO和/或Boc表达中断会导致面部异常，表现为轻度HPE。这项提议的具体目的是用胚胎学、遗传学和细胞生物学相结合的方法来检验这一假说。如果假说被证明是正确的，这项资助的影响将对细胞信号领域具有巨大的创新价值，并可能导致识别最终用于诊断、预防或治疗轻度HPE的分子靶点。

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.