Evolution of Axial Patterning

越来越多的证据表明，到目前为止所研究的后生动物的许多发育过程都涉及一组共同的或相关的机制中涉及的一组共同的调控基因。这些基因在后生动物进化过程中出现的时间有多早？它们的功能在多大程度上得到了保守？解决这些问题的一个有用的方法是研究蛇类动物的这种基因，这种动物是第一批有明确身体规划的动物。在线虫中，多头蛇特别有用，因为人们对发育过程有广泛的了解。这项拟议工作的总体目标是确定九头蛇轴形成和轴向模式背后的基因和机制是否与已发现的脊椎动物和节肢动物相似。这四个具体目标如下：在九头蛇中，可以研究在芽形成过程中轴的形成和轴的模式，芽是动物的无性繁殖形式。其中两个目标集中在澄清芽形成的各个方面。[1]在水母细胞的三个细胞谱系中，两个上皮谱系[外胚层和内胚层]起着明显的作用。间质细胞谱系的可能作用将通过改变或消除这一谱系的操作来研究。[2]在脊椎动物和Drosphila中发现的许多轴型基因的同源物已经从水蛇中分离出来，并显示在芽形成期间表达。通过将针对这些基因的反义寡核苷酸引入萌芽组织中，将研究它们特定作用的更直接证据。另外两个目标集中在分离与水龙的轴向模式有关的新基因。一种方法是寻找与背腹模式有关的基因的同源基因，这种模式在脊椎动物和果蝇中高度保守。另一项涉及利用青蛙胚胎第二轴的诱导来识别与轴向模式有关的九头蛇基因。任何用这两种方法分离的基因都将通过检测它们在各种发育情况下的表达模式以及使用反义方法获得更直接的信息来研究它们在多头蛇中轴模式中的作用。这一结果应该会扩大对轴形成的进化以及单轴动物如何进化为多轴动物的理解。

Accumulating evidence indicates is that a common set of regulatory genes involved in a common, or related, set of mechanisms underlie many of the developmental processes of the metazoans studied so far. How early did these genes arise during metazoan evolution and to what extent has their function been conserved? A useful approach to these questions is to study such genes in a cnidarian, the first group of animals to have a defined body plan. Among the cnidaria, hydra is particularly useful as the developmental processes are extensively understood. The overall aim of the proposed work is to determine if the genes and mechanisms underlying axis formation and axial patterning in hydra are similar to those found vertebrates and arthropods. The four detailed aims are the following.In hydra, axis formation and axial patterning can be studied during the process of bud formation, the animal's asexual form of reproduction. Two of the aims focus on clarifying aspects of bud formation. [1] Of the three cell lineages in hydra, the two epithelial lineages [ectoderm and endoderm] play an obvious role. A possible role of the interstitial cell lineage will be investigated by manipulations that alter or eliminate this lineage. [2] A number of homologues of axial patterning genes found in vertebrates and Drosphila have been isolated from hydra and show to be expressed during bud formation. More direct evidence of their particular roles will be investigated by introducing anti-sense oligonucleotides against such genes into budding tissue.The other two aims focus on the isolation of new genes involved in axial patterning in hydra. One approach will be to look for homologues of genes involved in dorsal-ventral patterning, which is in part, highly conserved among vertebrates and Drosophila. The other involves using the induction of a 2nd axis in frog embryos to identify hydra genes involved in axial patterning. Any genes isolated with either procedure will be examined for their role in axial patterning in hydra by examining their expression patterns in a variety of developmental situations as well as using the anti-sense approach to gain more direct information.The results should extend the understanding of the evolution of axis formation as well as how animals with a single axis evolved into animals with more than one axis.