Analysis of the function of the nodal gene during embryo

Nodal是一种转化生长因子（TGF）-β样蛋白，我们发现的逆转录病毒插入突变的基础上，并显示是必不可少的早期发育，在原肠胚形成中发挥重要作用。我们最近在小鼠胚胎发育中的节点信号传导方面的工作集中在功能降低的靶向突变等位基因（亚型）的分析上。胚胎是复合杂合子的这种亚型等位基因和一个完全无效的等位基因是能够发展过去的块原肠胚中看到的纯合子无效等位基因，但随后显示出各种发育异常。这使我们能够建立一个关键的作用，nodal在原肠胚形成开始后发生的发育过程中，包括前/后和左/右体轴的图案，以及中线中内胚层和肠内胚层的发展。然而，因为有一个普遍的减少，在每个节点的表达的许多领域的活动，我们的分析没有提供深入了解节点的表达是需要这些发展事件。为了进一步剖析节点功能的这些不同的时间和空间域，我们产生了一个条件突变（floxed）等位基因。携带该等位基因的小鼠正在与我们已经开发或从其他研究者获得的在发育胚胎的各个区域表达Cre重组酶的转基因菌株结合使用。对从用在原肠胚形成前胚胎上胚层（将产生所有胚层的细胞）中表达Cre的品系繁殖floxed小鼠获得的胚胎进行初步分析，揭示了先前观察到的亚形等位基因的所有相同表型。在胚胎外谱系中表达可能不需要早期淋巴结功能的可能性，现在正在通过使用在胚胎外内脏内胚层中特异性表达Cre的菌株来解决。正在进行的其他工作与其他组织特异性的Cre菌株。

Nodal is a transforming growth factor (TGF)-beta like protein that we discovered on the basis of a retroviral insertional mutation and showed to be essential for early development, playing a major role in gastrulation. Our recent work on nodal signaling in mouse embryonic development has focused on the analysis of a targeted mutant allele with reduced function (a hypomorph). Embryos that are compound heterozygotes for this hypomorphic allele and a completely null allele are capable of developing past the block at gastrulation seen in homozygotes for the null allele, but then show a variety of developmental abnormalities. This has allowed us to establish a critical role for nodal in developmental processes occurring after gastrulation begins, including patterning of the anterior/posterior and left/right body axes, and the development of the midline mesendoderm and gut endoderm. However, because there is a generalized reduction of activity in each of the many domains of nodal expression our analysis did not provide insight into where nodal expression is required for these developmental events. To dissect these various temporal and spatial domains of nodal function further, we generated a conditional mutant (floxed) allele. Mice carrying this allele are being used in conjunction with transgenic strains expressing Cre recombinase in various regions of the developing embryo, which we have developed or obtained from other investigators. Preliminary analysis of embryos obtained from breeding floxed mice with a strain expressing Cre in the pregastrulation embryonic epiblast, the cells that will give rise to all the germ layers, has revealed all of the same phenotypes observed earlier for the hypomorphic allele. The possibility that expression in extraembryonic lineages may not be required for early nodal function is now being addressed by the use of a strain expressing Cre specifically in the extraembryonic visceral endoderm. Additional ongoing work is being performed with Cre strains with other tissue specificities.