Holowacz T, Elinson R P
Department of Zoology, University of Toronto, Ontario, Canada.
Development. 1995 Sep;121(9):2789-98. doi: 10.1242/dev.121.9.2789.
The Xenopus egg contains a maternal dorsal determinant that is specifically localized to the vegetal cortex. We have previously shown that vegetal cortical cytoplasm can generate a full dorsal axis when it is injected into ventral vegetal blastomeres of a cleavage-stage embryo. In this study, we have defined further the properties of the dorsal activity. The cortical dorsal activity arises during oocyte maturation after germinal vesicle breakdown. When injected into the four extreme animal pole blastomeres of ultraviolet-ventralized 32-cell embryos, vegetal cortical cytoplasm partially rescued dorsal axial structures. As revealed by lineage tracing, these axial structures formed ectopically from the progeny of the cells that were injected. Injection of animal cortical cytoplasm had no effect. When mid-blastula (stage 8) animal caps from these injected embryos were isolated and cultured, both vegetal cortex-enriched and animal cortex-enriched animal caps produced only epidermis. Therefore vegetal cortex, on its own, is not a mesoderm inducer. Between stage 8 (blastula) and stage 10 (gastrula), a ventral mesoderm-inducing signal spreads from vegetal cells towards the animal pole. We tested whether this natural mesoderm-inducing factor interacts with the activity found in the vegetal cortex. Injection of vegetal cortex enhanced the formation of neural tissue and cement gland when animal caps were isolated at stage 10. When cultured from stage 8 in the presence of the ventral mesoderm-inducing fibroblast growth factor, animal caps enriched in vegetal cortex developed significantly more neural tissue and cement gland than ones enriched in animal cortex. These results indicate that the dorsal activity localized to the egg vegetal cortex alters the response of cells to mesoderm inducers.
非洲爪蟾卵含有一种母体背侧决定因子，该因子特异性定位于植物性皮层。我们之前已经表明，当将植物性皮层细胞质注射到卵裂期胚胎的腹侧植物性卵裂球中时，它能够产生完整的背轴。在本研究中，我们进一步确定了背侧活性的特性。皮层背侧活性在生发泡破裂后的卵母细胞成熟过程中产生。当将植物性皮层细胞质注射到经紫外线处理使其腹侧化的32细胞胚胎的四个极端动物极卵裂球中时，它部分挽救了背轴结构。谱系追踪显示，这些轴结构由注射细胞的后代异位形成。注射动物性皮层细胞质则没有效果。当从这些注射后的胚胎中分离出囊胚中期（第8期）的动物帽并进行培养时，富含植物性皮层和富含动物性皮层的动物帽都只产生了表皮。因此，植物性皮层自身并不是中胚层诱导物。在第8期（囊胚期）到第10期（原肠胚期）之间，一种腹侧中胚层诱导信号从植物性细胞向动物极扩散。我们测试了这种天然的中胚层诱导因子是否与在植物性皮层中发现的活性相互作用。当在第10期分离动物帽时，注射植物性皮层增强了神经组织和黏腺的形成。当从第8期开始在腹侧中胚层诱导性成纤维细胞生长因子存在的情况下进行培养时，富含植物性皮层的动物帽比富含动物性皮层的动物帽发育出明显更多的神经组织和黏腺。这些结果表明，定位于卵植物性皮层的背侧活性改变了细胞对中胚层诱导物的反应。
