THE ROLE OF THE HOMEOBOX SIX3 IN HOLOPROSENCEPHALY/CYCLOPIA

描述（由申请人提供）：前脑无裂畸形（HPE）是人类前脑最常见的胚胎畸形，由前脑不完全分裂引起。这种影响前索板和前神经外胚层发育的畸形包括不同程度的中线融合和影响前脑和面部的斜视。各种遗传因素和环境因素有助于HPE的病因学。在人类中，编码同源结构域转录因子的SIX 3基因突变与HPE相关。SIX 3促进HPE的遗传和细胞机制知之甚少。目前还不清楚突变体SIX 3蛋白是否具有亚型、反型或新型活性。SIX 3突变以显性方式导致HPE，但具有可变的遗传率和表达率，这一发现表明S/X3与其他遗传基因座相互作用。小鼠中Six 3的功能失活表明，前神经外胚层中Wnt信号传导的抑制对于脊椎动物前脑发育是必不可少的;然而，S/x3杂合小鼠没有表现出任何明显的形态学改变。在这个应用中，我们建议采用遗传学，胚胎学和分子生物学方法的组合来复制和表征HPE/cyclopia表型在小鼠和斑马鱼。目的1需要在体内和体外分子和转录表征所产生的HPE Six 3突变蛋白。目的2将产生Six 3介导的HPE的斑马鱼和小鼠模型。我们将使用这些模型来识别受突变体Six 3影响的组织和遗传途径。目的3集中于鉴定与突变的Six 3合作促进HPE的基因。这些拟议的研究将促进我们对受HPE-Six 3突变影响的信号通路的理解，并最终将提供额外的信息，用于HPE-Six 3突变携带者的遗传咨询，并降低这些出生缺陷的频率。

DESCRIPTION (provided by applicant): Holoprosencephaly (HPE) is the most common embryologic malformation of the forebrain in humans caused by incomplete cleavage of the prosencephalon. This malformation which affects the development of the prechordal plate and anterior neuroectoderm includes various degrees of midline fusion and cyclopia affecting the forebrain and face. Various genetic factors and environmental agents contribute to the etiology of HPE. In humans, mutations in the SIX3 gene encoding a homeodomain transcription factor have been associated with HPE. The genetic and cellular mechanisms of SIX3-promoted HPE are poorly understood. It remains unclear whether mutant SIX3 proteins have hypomorphic, antimorphic, or neomorphic activity. SIX3 mutations cause HPE in a dominant manner but with variable penetrance and expressivity, a finding that suggests that S/X3 interacts with other genetic loci. Functional inactivation of Six3 in mice has shown that repression of Wnt signaling in the anterior neuroectoderm is essential for vertebrate forebrain development; however, S/x3-heterozygous mice did not exhibit any obvious morphologic alteration. In this application, we propose to employ a combination of genetic, embryologic, and molecular methods to reproduce and characterize the HPE/cyclopia phenotype in mouse and zebrafish. Aim 1 entails in vivo and in vitro molecular and transcriptional characterization of the generated HPE Six3 mutant proteins. Aim 2 will generate zebrafish and mouse models of Six3-mediated HPE. We will use these models to identify tissues and genetic pathways affected by mutant Six3. Aim 3 focuses on the identification of genes that cooperate with mutated Six3 in promoting HPE. These proposed studies will advance our understanding of the signaling pathways affected by HPE-Six3 mutations and, ultimately, will provide additional information to be used with the genetic counseling of human carriers of HPE-SIX3 mutations and decrease the frequency of these birth defects.