Signal Transduction in Vertebrate Embryogenesis

描述(申请人提供)：这项建议涉及Axin和相关基因Axin2在哺乳动物胚胎发育过程中调节典型的Wnt信号转导途径中的作用。WNTs是一个分泌因子家族，在发育过程中对细胞的增殖、构型和分化起重要作用。Axin是蛋白质复合体的重要组成部分，通过调节β-catenin的水平来控制WNTs下游的细胞内信号传递。？-catenin是一种转录辅助激活因子，也是该途径中的关键效应因子。Axin2被认为具有类似的功能，尽管它的特征不是很好。在人类中，这两个基因的突变表明它们是肿瘤抑制因子，这与它们在负向调节Wnt途径中的作用一致。对Axin和Axin2基因突变的小鼠的分析表明，这些基因对早期的轴型以及颅面和大脑发育都很重要。颅面发育是一个复杂的过程，涉及表面外胚层、内胚层、中胚层和神经脊之间的相互作用，并且非常容易受到遗传和环境的干扰，因为颅面畸形是人类最常见的出生缺陷之一。Wnt信号通路通过几个小鼠的突变参与了头面部的发育。在这项提议中，将检验这一假说，即Axin和Axin2需要通过形成面部大部分的颅神经脊细胞来负向调节对某些Wnts的反应，并且Axin和Axin2的突变导致Wnt途径的不适当激活。这将通过对突变小鼠的分析，以及通过使用转基因方法有条件地操纵脑神经脊中的Wnt通路来解决。为了了解Axin和Axin 2在发育过程中是如何合作的，重要的是定义它们在功能上冗余的程度，这个问题将通过小鼠的基因替换策略来研究。最后，为了在体内测试Axin的特定结构域的重要性，这些结构域被认为介导了它与该途径的其他组件的功能相互作用，我们将产生几个新的Axin突变等位基因，并检查它们对小鼠胚胎发育的影响。

DESCRIPTION (provided by applicant): This proposal concerns the roles of Axin and the related gene Axin2 in regulating the canonical Wnt signal transduction pathway during mammalian embryogenesis. The Wnts are a family of secreted factors that play important roles in cell proliferation, patterning and differentiation during development. Axin is a critical component of a protein complex that controls intracellular signaling downstream of Wnts, by regulating the levels of ?-catenin, a transcriptional co-activator and a key effector in the pathway. Axin2 is believed to have a similar function, although it is not as well characterized. Mutations in both genes in humans have shown that they are tumor suppressors, consistent with their roles in negatively regulating the Wnt pathway. The analysis of mice with mutations in Axin and Axin2 have revealed that these genes are important for early axial patterning, as well as for craniofacial and brain development. Craniofacial development is a complex process that involves interactions between the surface ectoderm, endoderm, mesoderm and the neural crest, and it is highly susceptible to genetic and environmental perturbations, as craniofacial abnormalities are among the most common birth defects in humans. The Wnt signaling pathway has been implicated in craniofacial development through several mouse mutations. In this proposal, the hypothesis will be tested that Axin and Axin2 are required to negatively regulate the response to certain Wnts by the cranial neural crest cells that form much of the face, and that mutations in Axin and Axin2 lead to inappropriate activation of the Wnt pathway. This will be addressed by analysis of mutant mice, as well as through the conditional manipulation of the Wnt pathway in the cranial neural crest, using transgenic approaches. To understand how Axin and Axin 2 cooperate during development, it is important to define the extent to which they are functionally redundant, and this issue will be investigated through a gene replacement strategy in mice. Finally, to test in vivo the importance of specific domains of Axin that are believed to mediate its functional interactions with other components of the pathway, several novel mutant alleles of Axin will be generated, and examined for their effects on mouse embryogenesis.