Signal Transduction in Vertebrate Embryogenesis

描述（由申请人提供）：本提案涉及Axin和相关基因Axin 2在哺乳动物胚胎发生期间调节经典Wnt信号转导途径中的作用。Wnt是一个分泌因子家族，在发育过程中的细胞增殖、模式化和分化中发挥重要作用。Axin是一种蛋白复合物的关键成分，通过调节β-淀粉样蛋白的水平，控制Wnt下游的细胞内信号传导。连环蛋白是一种转录辅激活因子，也是该通路中的关键效应子。Axin 2被认为具有类似的功能，尽管它没有被很好地表征。人类两种基因的突变表明它们是肿瘤抑制因子，与它们在负调节Wnt途径中的作用一致。对Axin和Axin 2突变小鼠的分析表明，这些基因对早期轴向模式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，中胚层和神经嵴之间的相互作用，并且它非常容易受到遗传和环境干扰，因为颅面畸形是人类最常见的出生缺陷之一。Wnt信号通路通过几种小鼠突变与颅面发育有关。在该提案中，将测试以下假设：Axin和Axin 2需要负调节形成面部大部分的颅神经嵴细胞对某些Wnt的反应，并且Axin和Axin 2的突变导致Wnt通路的不适当激活。这将通过分析突变小鼠，以及通过有条件的操作的Wnt通路在颅神经嵴，使用转基因方法来解决。为了了解Axin和Axin 2在发育过程中如何合作，重要的是要确定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进行研究。最后，为了在体内测试被认为介导其与途径的其他组分的功能相互作用的Axin的特定结构域的重要性，将产生Axin的几个新的突变等位基因，并检查它们对小鼠胚胎发生的影响。

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.