Molecular analysis of a self- organizing signaling pathway for Xenopus axial patterning from egg to tailbud

• 成果类型: Article
• 署名作者: Azbazdar, Yagmur; De Robertis, Edward M.
• 署名单位: University of California System; University of California Los Angeles; University of California Los Angeles Medical Center; David Geffen School of Medicine at UCLA
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9762
• DOI: 10.1073/pnas.2408346121
• 发表日期: 2024-07-09
• 关键词: negative feedback regulator; beta-catenin; wnt; gene; mesoderm; chordin; expression; induction; bmp; antagonist

摘要

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 beta- 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 beta- 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 beta- catenin- depleted embryos. Surprisingly, this rescue occurred in the absence of any beta- catenin transcriptional activity as measured by beta- 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 beta- 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.