Molecular mechanism of morphogenetic movements in amphibian embryos

原肠胚形成是动物发育过程中最活跃的形态发生运动，是机体计划的开始。为了分析非洲爪蟾原肠胚形成的分子机制，我们通过在非洲爪蟾中的表达筛选，分离出一种编码POZ/锌指蛋白的kuppel样转录因子champignon （cpg）。cpg过表达导致原肠胚形成受到干扰。对照胚胎和注射cpg的11.5期胚胎的组成蛋白比较发现，注射cpg的胚胎中一个61 kDa蛋白斑点基本移位，表明注射cpg使61 kDa蛋白去磷酸化。该61 kDa蛋白的部分氨基酸序列（23 mer）与推测的爪蟾STI1蛋白完全一致，该蛋白是应激诱导磷酸化蛋白（STI1）、Hsp70/ hsp90组织蛋白（Hop）或转化敏感蛋白的同源物。STI1/Hop将Hsp70和Hsp90结合，并调节Hsp90伴侣蛋白的功能，已知Hsp90伴侣蛋白与细胞骨架结合。因此，cpg对原肠胚形成的抑制作用是通过XSTI1的去磷酸化介导的。这些结果表明，Hsp90伴侣参与了形态发生运动的控制。我们还克隆了一个新的基因Xoom，它编码一种跨膜蛋白。在爪蟾胚胎中注射Xoom反义RNA可降低Xoom蛋白的表达，引起原肠胚发育缺陷，但对中胚层标记基因的复归和表达没有影响。不同实验条件下细胞形态的比较表明，细胞扩散的抑制主要发生在反义rna注射胚胎的外胚层。细胞学检查显示，注射反义rna的胚胎外胚层细胞中f -肌动蛋白紊乱。这些结果表明Xoom通过调节肌动蛋白丝组织在外胚层细胞的表观运动中起重要作用。

Gastrulation is the most dynamic morphogenetic movement and initiates the body plan in animal development. In order to analyze the molecular mechanism of gastrulation, we have isolated a novel kuppel-like transcription factor, champignon (cpg), that encodes POZ/Zinc finger protein by expression screening in Xenopus laevis. Overexpression of cpg resulted in interference with gastrulation. Comparison of the constituent proteins from control embryos and cpg-injected embryos at stage 11.5 revealed that a 61 kDa protein spot was shifted basically in cpg-injected embryos suggesting that the 61 kDa protein was dephosphorylated by cpg-injection. Partial amino acid sequence (23 mer) of the 61 kDa protein accords 100 % with that of putative Xenopus STI1 protein which is a homolog of stress-induced phosphoprptein (STI1), Hsp70/Hsp90-organizing protein (Hop), or transformation-sensitive protein. The STI1/Hop combines Hsp70 with Hsp90 and modulates the function of Hsp90 chaperone which is known to bind to cytoskeletons. Thus the inhibitory role of cpg on gastrulation is mediated by dephosphorylation of XSTI1. These results suggest that the Hsp90 chaperone is involved in the control of morphogenetic movements.We have also cloned a novel gene, Xoom, which encodes a transmembrane protein. Injection of Xoom antisense RNA into Xenopus embryos reduced the Xoom protein and caused gastrulation defects without any influence on the involution and expression of mesodermal marker genes. Comparison of cell shape among various experimental conditions showed that inhibition of cell spreading occurs specifically in the outer ectodermal layer of the antisense RNA-injected embryo. Cytological examination indicated disorgatrization of F-actin in the ectodermal cells of the antisense RNA-injected embryo. These results suggest that Xoom plays an important role in the epibolic movement of ectodermal cells through some regulation of actin filament organizaiion.