非洲爪猿胚胎提供了一种有利的材料,可以解剖导致背腹侧(D-V)和前后(A-P)细胞分化的顺序步骤。这里,我们使用功能丧失和功能获得方法分析了参与该过程的信号通路.最初的步骤是由Hwa提供的,一种跨膜蛋白,当显微注射到胚胎的腹侧时,会强烈激活早期β-catenin信号,导致完整的双轴。接下来的步骤是非洲爪狼结节相关生长因子的激活,它可以挽救β-连环蛋白的消耗,并且本身被细胞外Nodal拮抗剂Cerberus-Short和Lefty阻断。在原肠胚形成期间,Spemann-Mangold组织者分泌了一种生长因子拮抗剂的混合物,其中BMP拮抗剂Chordin和Noggin可以同时挽救β-catenin耗尽胚胎中的D-V和A-P组织。令人惊讶的是,这种拯救发生在没有任何β-连环蛋白转录活性的情况下,如β-连环蛋白激活的荧光素酶报告基因所测量的。Wnt拮抗剂Dickkopf(Dkkl)通过抑制晚期Wnt信号与早期Hwa信号强烈协同。Sizzled(Szl)的耗尽,Tolloidchordinase的拮抗剂,对Hwa和Dkk1的协同作用具有认同感。BMP4mRNA注射阻断了Hwa诱导的异位轴,和Dkk1抑制BMP信号晚期,但不是很早,在原肠胚形成期间。有几个意想不到的发现,例如,在β-连环蛋白敲低胚胎中,通过Chordin或Nodal诱导了良好的完整胚胎轴,氯化锂(LiCl)的休眠是由节点介导的,Dkk1通过调节晚期BMP信号发挥其正向和反向作用,而Dkk1表型需要Szl。
Xenopus embryos provide a favorable material to dissect the sequential steps that lead to dorsal-ventral (D-V) and anterior-posterior (A-P) cell differentiation. Here, we analyze the signaling pathways involved in this process using loss-of-function and gain-of-function approaches. The initial step was provided by Hwa, a transmembrane protein that robustly activates early β-catenin signaling when microinjected into the ventral side of the embryo leading to complete twinned axes. The following step was the activation of Xenopus Nodal-related growth factors, which could rescue the depletion of β-catenin and were themselves blocked by the extracellular Nodal antagonists Cerberus-Short and Lefty. During gastrulation, the Spemann-Mangold organizer secretes a cocktail of growth factor antagonists, of which the BMP antagonists Chordin and Noggin could rescue simultaneously D-V and A-P tissues in β-catenin-depleted embryos. Surprisingly, this rescue occurred in the absence of any β-catenin transcriptional activity as measured by β-catenin activated Luciferase reporters. The Wnt antagonist Dickkopf (Dkk1) strongly synergized with the early Hwa signal by inhibiting late Wnt signals. Depletion of Sizzled (Szl), an antagonist of the Tolloid chordinase, was epistatic over the Hwa and Dkk1 synergy. BMP4 mRNA injection blocked Hwa-induced ectopic axes, and Dkk1 inhibited BMP signaling late, but not early, during gastrulation. Several unexpected findings were made, e.g., well-patterned complete embryonic axes are induced by Chordin or Nodal in β-catenin knockdown embryos, dorsalization by Lithium chloride (LiCl) is mediated by Nodals, Dkk1 exerts its anteriorizing and dorsalizing effects by regulating late BMP signaling, and the Dkk1 phenotype requires Szl.