THE ROLE OF THE HOMEOBOX SIX3 IN HOLOPROSENCEPHALY/CYCLOPIA

描述（由申请人提供）：前脑全裂畸形（HPE）是人类前脑最常见的胚胎畸形，由前脑不完全切割引起。这种影响脊索前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独眼。各种遗传因素和环境因素有助于HPE的病因。在人类中，编码同源结构域转录因子的SIX3基因突变与HPE有关。six3促进HPE的遗传和细胞机制尚不清楚。目前尚不清楚突变体SIX3蛋白是否具有半形、反形或新形活性。SIX3突变以显性方式引起HPE，但具有可变的外显率和表达性，这一发现表明S/X3与其他遗传位点相互作用。小鼠Six3的功能失活表明，前神经外胚层中Wnt信号的抑制对脊椎动物前脑发育至关重要；而S/x3杂合小鼠未表现出明显的形态学改变。在这项应用中，我们建议采用遗传学、胚胎学和分子方法的结合来复制和表征小鼠和斑马鱼的HPE/独眼表型。目的1需要在体内和体外对生成的HPE Six3突变蛋白进行分子和转录表征。目的2将生成six3介导的HPE斑马鱼和小鼠模型。我们将使用这些模型来识别受突变体Six3影响的组织和遗传途径。目的3着重于鉴定与突变的Six3协同促进HPE的基因。这些拟议的研究将促进我们对受HPE-Six3突变影响的信号通路的理解，并最终为HPE-Six3突变的人类携带者提供遗传咨询和减少这些出生缺陷的频率提供额外的信息。

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.