THE ROLE OF THE HOMEOBOX SIX3 IN HOLOPROSENCEPHALY/CYCLOPIA

描述(申请人提供)：无前脑畸形(HPE)是人类最常见的前脑胚胎畸形，由前脑的不完全分裂引起。这种畸形影响前脊索板和前神经外胚层的发育，包括不同程度的中线融合和影响前脑和面部的睫状视。多种遗传因素和环境因素参与了HPE的发病机制。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促进的HPE的遗传和细胞机制尚不清楚。目前尚不清楚突变的Six3蛋白是否具有亚形态、抗形态或新形态活性。Six3突变以显性方式引起HPE，但具有不同的外显性和表现性，这一发现表明S/X3与其他遗传座位相互作用。SIX3在小鼠的功能失活表明，抑制前神经外胚层中的Wnt信号是脊椎动物前脑发育所必需的；然而，S/x3杂合子小鼠没有表现出任何明显的形态变化。在这一应用中，我们建议使用遗传学、胚胎学和分子学相结合的方法来复制和表征小鼠和斑马鱼的HPE/旋毛症表型。目的1对所产生的HPE Six3突变蛋白进行体内和体外的分子和转录鉴定。Aim 2将产生Six3介导的斑马鱼和小鼠HPE模型。我们将使用这些模型来识别受突变Six3影响的组织和遗传途径。目的3重点寻找与突变的Six3基因协同促进HPE的基因。这些拟议的研究将促进我们对HPE-Six3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-Six3突变携带者的遗传咨询，并减少这些出生缺陷的发生率。

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.