McGrew L L, Otte A P, Moon R T
Department of Pharmacology, University of Washington School of Medicine, Seattle 98195.
Development. 1992 Jun;115(2):463-73. doi: 10.1242/dev.115.2.463.
This study characterizes the temporal and spatial expression during early Xenopus development of Xwnt-4, a member of the Wnt gene family. The Xwnt-4 protein contains all of the sequence motifs that are hallmarks of the Wnt gene family and is 84% identical to the mouse homolog, Wnt-4. The highest level of Xwnt-4 expression occurs during the early neurula stage of development although its expression persists throughout embryogenesis and can be found in the adult testis, brain and epithelium. Consistent with its localization to head and dorsal regions of microdissected embryos, the expression of Xwnt-4 is enhanced in anterodorsalized embryos resulting from treatment with LiCl, and the expression of Xwnt-4 is suppressed in UV-ventralized embryos that lack anterior neural tissue. These results suggested that expression of Xwnt-4 is dependent on the induction of neural tissue. This idea was tested using induction experiments with dorsal or ventral ectoderm from a stage 10 embryo, recombined with dorsal marginal zone mesoderm from the same embryo. Recombinant tissue and ectoderm alone were cultured until stage 14, when Xwnt-4 expression was assayed using Northern analysis. In the recombinant assay, Xwnt-4 expression does not occur in the uninduced ectoderm but is expressed in both the dorsal and ventral recombinants. Xwnt-4 expression in neural ectoderm was confirmed in isolated, induced neural ectoderm, dissected away from the dorsal mesoderm, in a stage 12.5 embryo. Whole-mount in situ hybridization confirmed the dissection studies and demonstrated that Xwnt-4 transcripts are expressed in the dorsal midline of the midbrain, hindbrain and the floor plate of the neural tube. Collectively, the data indicate that Xwnt-4 is a unique member of the Wnt family whose expression is dependent on neural induction. The specific pattern of expression following neural induction suggests that Xwnt-4 plays a role in the early patterning events responsible in the formation of the nervous system in Xenopus.
本研究对爪蟾早期发育过程中Wnt基因家族成员Xwnt-4的时空表达进行了表征。Xwnt-4蛋白包含Wnt基因家族所有标志性的序列基序，并且与小鼠同源物Wnt-4有84%的同一性。Xwnt-4表达的最高水平出现在发育的早期神经胚阶段，尽管其表达在整个胚胎发生过程中持续存在，并且在成年睾丸、大脑和上皮组织中也能发现。与其在显微解剖胚胎的头部和背侧区域的定位一致，用LiCl处理导致的前背化胚胎中Xwnt-4的表达增强，而在缺乏前神经组织的紫外线腹化胚胎中Xwnt-4的表达受到抑制。这些结果表明Xwnt-4的表达依赖于神经组织的诱导。使用来自10期胚胎的背侧或腹侧外胚层与同一胚胎的背侧边缘区中胚层进行重组诱导实验来验证这一想法。重组组织和单独的外胚层培养到14期，此时使用Northern分析检测Xwnt-4的表达。在重组实验中，未诱导的外胚层中不发生Xwnt-4的表达，但在背侧和腹侧重组体中均有表达。在12.5期胚胎中，从背侧中胚层分离出的分离诱导神经外胚层中证实了神经外胚层中Xwnt-4的表达。整体原位杂交证实了解剖研究，并表明Xwnt-4转录本在中脑、后脑的背侧中线和神经管的底板中表达。总体而言，数据表明Xwnt-4是Wnt家族的一个独特成员，其表达依赖于神经诱导。神经诱导后特定的表达模式表明Xwnt-4在爪蟾神经系统形成所涉及的早期模式形成事件中发挥作用。
