Murate M, Kishimoto Y, Sugiyama T, Fujisawa T, Takahashi-Iwanaga H, Iwanaga T
Department of Life Sciences, The Graduate University for Advanced Studies, Mishima, Japan.
J Cell Sci. 1997 Aug;110 ( Pt 16):1919-34. doi: 10.1242/jcs.110.16.1919.
Hydra tissue consists of the ectodermal and the endodermal layers. When the two layers were separated by procaine treatment and then recombined, the ectodermal epithelial cells spread as a single cell layer over the endoderm as in epiboly in vertebrate embryogenesis, and the resultant spherical structure subsequently regenerated into a complete hydra. In this study, light and electron microscopy were used to examine the structural changes which took place in the cells and tissue during this epibolic ectodermal spreading process. Within a few hours after tissue recombination, the endoderm underwent dramatic changes; it lost its epithelial sheet organization, and turned into a mass of irregularly shaped cells without the apical-basal cell polarity initially present. In contrast, the ectoderm maintained its basic epithelial sheet organization as it spread over the endoderm. Later, the endodermal epithelial cells reorganized themselves into a single-layered epithelial sheet underneath the spreading ectodermal layer. The resultant spherical structure consisted of a single layer of ectodermal epithelial cells outside, a single layer of endodermal epithelial cells inside, and an empty cavity in the center as in normal hydra tissue. This structure regenerated into hydra in the following days. These and other observations demonstrate that the two-layered epithelial sheet organization is highly dynamic, and that its stability is maintained by strong interactions between the two layers in normal hydra. It is suggested that this dynamic nature of the hydra tissue, particularly the high plasticity of the endodermal epithelial sheet organization, may be an important element for the high regenerative capacity of this organism.
水螅组织由外胚层和内胚层组成。当这两层通过普鲁卡因处理分离后再重新组合时，外胚层上皮细胞会像脊椎动物胚胎发育中的外包过程一样，作为单层细胞铺展在内胚层上，随后形成的球形结构会再生为完整的水螅。在本研究中，利用光学显微镜和电子显微镜来检查在这种外包性外胚层铺展过程中细胞和组织发生的结构变化。组织重组后数小时内，内胚层发生了显著变化；它失去了上皮细胞层的组织结构，变成了一团形状不规则的细胞，最初存在的顶端 - 基部细胞极性消失。相比之下，外胚层在铺展在内胚层上时保持了其基本的上皮细胞层组织结构。后来，内胚层上皮细胞在内胚层铺展层下方重新组织成单层上皮细胞层。形成的球形结构由外层的单层外胚层上皮细胞、内层的单层内胚层上皮细胞以及中间的一个空腔组成，如同正常水螅组织一样。这个结构在接下来的几天里再生为水螅。这些以及其他观察结果表明，两层上皮细胞层的组织结构具有高度的动态性，并且在正常水螅中其稳定性是由两层之间的强相互作用维持的。有人提出，水螅组织的这种动态特性，特别是内胚层上皮细胞层组织结构的高可塑性，可能是该生物体高再生能力的一个重要因素。
