THE ROLE OF XENOPUS-POSTERIOR (XPO) IN EARLY FROG DEVELOPMENT

两栖动物的经典胚胎学研究表明， 前后轴形成的一个步骤是 预期中胚层 然后，背中胚层通过以下方式转移这种极性： 在漱口期间对上覆的外胚层的诱导。 分子 中胚层极性的性质尚不清楚， 特定的基因产物，如同源异型盒基因Xhox 3，被认为是 发挥作用。 我们分离出了另一种潜在的 前后轴形成的调节器，Xenopus-后（Xpo）。 的 Xpo蛋白属于一类新的发育表达蛋白。 它在囊胚中期过渡期被激活， 从原肠胚形成中期到神经胚形成。 其表达仅限于 后背中胚层和外胚层。 一个手指的复制品 “CCHC”型基序位于羧基末端。 相关 基序存在于所有逆转录病毒的核衣壳蛋白中， 结构域在逆转录病毒复制和细胞增殖中起重要作用。 核酸结合蛋白（CNBP），一种与甾醇结合的蛋白质 调节元件。 与轴形成的其他潜在调节器一样， 通过用碱性磷酸酶处理外胚层外植体诱导XPO表达， FGF和多肽生长因子，发现在培养基条件下， 非洲爪蟾XTC细胞系。 总的来说，Xpo的特性表明， 可能在前后轴的组织中发挥作用， 发展

Classical embryology studies in amphibians have demonstrated that important step in anteroposterior axis formation is the polarization of the prospective mesoderm. The dorsal mesoderm then transfers this polarity by induction to the overlying ectoderm during gartrulation. The molecular nature of the mesodermal polarity is not known although a number of specific gene products, such as the homeobox gene, Xhox 3, are thought to play a role. We have isolated and characterized another potential regulator of anteroposterior axis formation, Xenopus-posterior (Xpo). The Xpo protein belongs to a new class of developmentally expressed proteins. It is activated at mid-blastula transition and is expressed maximally during mid-gastrulation to neurulation. Its expression is restricted to the posterior dorsal mesoderm and ectoderm. A single copy of a finger motif, of the "CCHC" type, is located in the carboxyl terminus. Related motifs are found in the nucleocapsid protein of all retroviruses where this domain serves an essential role in retroviral replication and in cellular nucleic acid binding protein (CNBP), a protein that binds to the sterol regulatory element. As with other potential regulators of axis formation, Xpo expression is induced in ectodermal explants by treatment with basic FGF and polypeptide growth factors found in the medium conditioned by the Xenopus XTC cell line. Taken together, Xpo's properties suggest that it may play a role in the organization of the anteroposterior axis during development.