title: Nodal signaling in Xenopus gastrulae is cell-autonomous and patterned by beta-catenin.
abstract: The classical three-signal model of amphibian mesoderm induction and more recent modifications together propose that an activin-like signaling activity is uniformly distributed across the vegetal half of the Xenopus blastula and that this activity contributes to mesoderm induction. In support of this, we have previously shown that the activin-response element (DE) of the goosecoid promoter is uniformly activated across the vegetal half of midgastrula-stage embryos. Here, we further examine the nature of this activity by measuring DE activation by endogenous signals over time. We find that the spatiotemporal pattern of DE activation is much more dynamic than was previously appreciated and also conclude that DE(6X)Luc activity reflects endogenous nodal signaling in the embryo. Using both the DE(6X)Luc construct and endogenous Xbra and Xgsc expression as read-outs for nodal activity, and the cleavage-mutant version of Xnr2 (CmXnr2) to regionally suppress endogenous nodal activity, we demonstrate that nodal signals act cell-autonomously in Xenopus gastrulae. Nodal-expressing cells are unable to rescue either reporter gene activation or target gene expression in distant nodal-deficient cells, suggesting that nodals function at short range in this context. Finally, we show that DE activation by endogenous signals occurs in the absence of dorsal beta-catenin-mediated signaling, but that the timing of dorsal initiation is altered. We conclude that nodal signals in Xenopus gastrulae function cell autonomously at short ranges and that the spatiotemporal pattern of this signaling along the dorsoventral axis is regulated by maternal Wnt-like signaling.
authors.affiliation: Department of Developmental and Cell Biology, University of California, Irvine, California 92697-2300, USA.
authors.forename: Minako K
authors.initials: MK
authors.lastname: Hashimoto-Partyka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yuge
authors.forename: Ken W Y
authors.initials: KW
authors.lastname: Cho
mesh_terms: D000818:Animals; D001483:Base Sequence; D003598:Cytoskeletal Proteins / Q000502:physiology*; D017931:DNA Primers; D005775:Gastrula / Q000166:cytology*; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D055457:Nodal Protein; D011518:Proto-Oncogene Proteins / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D015534:Trans-Activators / Q000502:physiology*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000502:physiology*; D051153:Wnt Proteins; D014981:Xenopus; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: C495266:CTNNB1 protein, Xenopus; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D055457:Nodal Protein; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin