Molecular and cellular analyses of the Wnt signaling pathway that regulates Xenopus gastrulation

原肠胚形成是发育中第一个主要的形态发生过程，需要协调细胞运动，最终形成三个胚层。在非洲爪蟾原肠胚形成过程中，胚胎赤道区的细胞形成前缘，并内卷到胚胎的内部区域。然后，它们迁移到囊胚腔的顶部，朝向动物的两极。轴向中胚层细胞首先被极化，然后在径向和中外侧方向上插入，以引起背侧边缘区的急剧延伸，其被定义为会聚延伸，以建立身体平面的前后轴。已知会聚延伸过程受Wnt信号通路调节。我们已经发现Rab家族中的一种GTP酶对于Wnt信号通路是必需的。已知Rab家族GTP酶调节膜运输的许多步骤，因此我们分析了Rab GTP酶在非洲爪蟾原肠胚形成中的作用。我们发现xRab 40是Rab 40的爪蟾同源物，是正常原肠胚形成所必需的。xRab 40定位于高尔基体，并被发现与ElonginB/C和Cullin 5，E3泛素连接酶的组分相互作用。非洲爪蟾Cullin 5的功能丧失，命名为xCullin 5，表型复制并与xRab 40敲低协同。此外，我们发现，这些是必不可少的非经典Wnt信号通路。这些结果表明，xRab 40和xCullin 5在高尔基体上形成了一种遍在蛋白连接酶复合物，并通过调节这些膜蛋白在原肠胚形成过程中发挥重要作用。

Gastrulation is the first major morphogenetic process in development that entails coordinated cell movements and, ultimately, three germ layers are formed. During Xenopus gastrulation, cells in an equatorial region of the embryo form the leading edge and involute to the inner region of the embryo. They then migrate to the roof of the blastocoel towards the animal poles. Axial mesoderm cells are first polarized and then intercalated in radial and mediolateral directions to cause dramatic extension of the dorsal marginal zone, which is defined as convergent extension, in order to establish the anterior-posterior axis of the body plan. It is known that the process of convergent extension is regulated by the Wnt signaling pathway. We have found that one of the Rab family GTPases is essential for the Wnt signaling pathway. Rab family GTPases are known to regulate many steps of membrane trafficking, and thus we analyzed the roles of Rab GTPases in Xenopus gastrulation. We found that xRab40, a Xenopus homolog of Rab40, was required for normal gastrulation. xRab40 was localized at the Golgi apparatus and was found to interact with ElonginB/C and Cullin5, components of E3 ubiquitin ligases. Loss-of-function of Xenopus Cullin5, designated xCullin5, phenocopied and synergized with xRab40 knockdown. Furthermore, we found that these are essential for the noncanonical Wnt signaling pathway. These results demonstrate that xRab40 and xCullin5 form a ubiquitin ligase complex on the Golgi apparatus and play essential roles during gastrulation through regulating these membrane proteins.