Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697, USA.
Dev Biol. 2010 Apr 1;340(1):116-24. doi: 10.1016/j.ydbio.2009.12.036. Epub 2010 Jan 4.
In an adult hydra the head organizer, located in the hypostome, is constantly active in maintaining the structure of the animal in the context of its steady state tissue dynamics. Several Wnt genes, TCF, and elevated levels of beta-catenin are expressed in the hypostome as well as during the formation of a new organizer region in developing buds suggesting they play a role in the organizer. Transgenic hydra were generated in which a modified hydra beta-catenin gene driven by an actin promoter is continuously expressed at a high level throughout the animal. These animals formed heads and secondary axes in multiple locations along the body column. Transplantation experiments indicate they have a high and stable level of head organizer activity throughout the body columns. However, none of the Wnt genes are expressed in the body columns of these transgenic animals. Further, in alsterpaullone-treated animals, which results in a transient rise in head organizer activity throughout the body column, the time of expression of the Wnt genes is much shorter than the time of the elevated level of head inducing activity. These results for the first time provide direct functional evidence that beta-catenin plays a crucial role in the maintenance and activity of the head organizer and suggest that Wnt ligands may be required only for the initiation but not in maintenance of the organizer in Hydra.
在成年水螅中，位于口盘的头部组织者持续活跃，以维持动物在其稳定状态组织动力学中的结构。在口盘以及发育芽中形成新的组织者区域的过程中，表达了几个 Wnt 基因、TCF 和β-连环蛋白的高水平，表明它们在组织者中发挥作用。生成了转基水螅，其中由肌动蛋白启动子驱动的修饰水螅β-连环蛋白基因在整个动物中持续高水平表达。这些动物在身体柱的多个位置形成头部和次级轴。移植实验表明，它们在整个身体柱中具有高水平和稳定的头部组织者活性。然而，这些转基因动物的身体柱中没有表达任何 Wnt 基因。此外，在 alsterpaullone 处理的动物中，整个身体柱中的头部组织者活性会短暂升高，Wnt 基因的表达时间比头部诱导活性升高的时间短得多。这些结果首次提供了直接的功能证据，表明β-连环蛋白在头部组织者的维持和活性中发挥着关键作用，并表明 Wnt 配体可能仅在 Hydra 中组织者的启动而不是维持中是必需的。
