Hainski A M, Moody S A
Department of Anatomy and Cell Biology, University of Virginia School of Medicine, Charlottesville 22908.
Development. 1992 Oct;116(2):347-55. doi: 10.1242/dev.116.2.347.
The initial steps of dorsal axis formation are controlled by localized maternal determinants in Drosophila, and a similar process has been proposed in Xenopus. The present study demonstrates that there are axis-inducing RNA molecules located in a specific dorsal midline, animal blastomere (D1.1) of the 16-cell-stage embryo. This blastomere, although in the animal hemisphere at cleavage stages, populates most of the dorsal lip of the blastopore, the region of Spemann's organizer, during gastrulation, and is the major progenitor for dorsal mesodermal tissues. Cytosol from this blastomere causes ventral cells to take a more dorsal fate. RNA from this blastomere induces a secondary axis when injected into ventral blastomeres and restores the dorsal axis in UV-irradiated embryos. In Xenopus, activin beta B, goosecoid and Xwnt-8 RNAs can ectopically induce a dorsal axis; however, none is a maternal transcript. Therefore, the D1.1 blastomere probably contains dorsal determinant(s) that are either maternal members of these gene families, or other presently unknown molecule(s). Regardless of the identity of the determinant(s), this study presents the first indication that Xenopus maternal RNAs in the dorsal animal hemisphere are able to organize the dorsal axis.
果蝇中背轴形成的初始步骤由局部母源决定因子控制，并且在非洲爪蟾中也提出了类似的过程。本研究表明，在16细胞期胚胎的特定背侧中线动物卵裂球（D1.1）中存在诱导轴形成的RNA分子。这个卵裂球在卵裂期虽然位于动物半球，但在原肠胚形成期间占据了胚孔背唇的大部分，即施佩曼组织者所在的区域，并且是背侧中胚层组织的主要祖细胞。来自这个卵裂球的胞质溶胶会使腹侧细胞具有更背侧的命运。当将来自这个卵裂球的RNA注射到腹侧卵裂球中时会诱导出一条次生轴，并且能恢复紫外线照射胚胎的背轴。在非洲爪蟾中，激活素βB、鹅膏蕈氨酸和Xwnt - 8 RNA可以异位诱导背轴；然而，它们都不是母源转录本。因此，D1.1卵裂球可能含有背侧决定因子，这些决定因子要么是这些基因家族的母源成员，要么是其他目前未知的分子。无论决定因子的身份如何，本研究首次表明非洲爪蟾动物半球背侧的母源RNA能够构建背轴。
