XB-ART-9447Biochem Biophys Res Commun 2001 Mar 02;2813:714-9. doi: 10.1006/bbrc.2001.4386.
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In synergy with noggin and follistatin, Xenopus nodal-related gene induces sonic hedgehog on notochord and floor plate.
In early development of vertebrates, sonic hedgehog functions in dorsal-ventral patterning of dorsal tissue (nervous system and somites). In Xenopus, sonic hedgehog (Xshh) is first expressed in the Spemann organizer/notochord and floor plate. We report here the mechanism governing Xshh mRNA induction in these regions. In animal cap assays, the antagonizing BMPs signal was not sufficient to induce Xshh mRNA expression; however, it could induce Xshh mRNA expression in the presence of Xnr-1. In whole embryos, when secondary axes were induced by coexpressing noggin and Xnr-1 or follistatin and Xnr-1, Xshh mRNA expression was observed in the notochord and floor plate within the induced axes. It seems apparent that spatially restricted Xshh mRNA expression is determined as intersection of the two signals.
PubMed ID: 11237716
Article link: Biochem Biophys Res Commun
Species referenced: Xenopus
Genes referenced: eomes fst ncam1 nodal nodal1 nog shh
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|FIG. 1. RT-PCR analysis for Xshh expression in vegetal explants and animal caps. (A) 1 ng mRNAs encoding tAR7 and tBR2 was injected into each four vegetal blastomeres of an 8-cell embryo. Vegetal explants were dissected at stage 8.5 and collected at the early tailbud period. (B) 4 ng mRNAs encoding tAR7 and tBR2 were injected into the animal pole of 1-cell embryo. Animal caps were dissected at stage 8.5 and collected at early tailbud period. (C) Induction of Xshh expression in animal caps derived from embryos coinjected with Xnr-1 and noggin, or Xnr-1 and follistatin. Ornithine decarboxylase (ODC) served as an ubiquitous control.|
|FIG. 2. Localization of N-CAM mRNAs by whole mount in situ hybridization. (A) Uninjected Xenopus embryos. (B) Embryos injected with 10 pg Xnr-1 mRNA. N-CAM mRNAs were expressed in both primary axis (arrow) and secondary axis (arrowhead). Other partial secondary axes (induced by noggin, follistatin, both Xnr-1 and noggin, both Xnr-1 and follistatin) were similar (data not shown). (C) Embryos injected with 10 pg Xnr-1 mRNA and 10 pg noggin mRNA. N-CAM mRNAs were expressed in both primary axis (arrow) and secondary axis (arrowhead). (D) Dorsal-expanded embryos formed by injection with 10 pg Xnr-1 and 100 pg follistatin mRNA. N-CAM mRNAs expressing regions were seen to spread (asterisk).|
|FIG. 3. Localization of Xshh mRNAs by whole mount in situ hybridization. (A) Uninjected embryos. (B) Cross-sectioning through the trunk of A. (C) Embryos injected with 10 pg Xnr-1 mRNA. Xshh mRNAs were expressed only in the primary axis. (D) Cross-sectioning through the trunk of C. Neural tissue consisting of the structure of the tube was induced (arrowhead). (E) Crosssectioning through embryos which induced partial secondary axis by 10 pg noggin mRNA. (F) Embryos injected with 10 pg Xnr-1 mRNA and 10 pg Noggin mRNA. Complete (upper) or partial (lower) secondary axes were induced. Xshh mRNAs were expressed in both primary axis and secondary axis. (G) Crosssectioning through the trunk of F. (H) Dorsal-expanded embryos formed by injection with 10 pg Xnr-1 mRNA and 100 pg follistatin mRNA. Xshh mRNAs were expressed in an ectopic manner on the lateral side of the normal expression (asterisk). (I) Crosssectioning through the trunk of H. Ectopic small notochord was formed along the side of the primary neural tube. (J) Crosssectioning through another dorsal-expanded embryo coinjected Xnr-1 and follistatin mRNA. Large notochord was induced. Arrow and arrowhead indicate primary and secondary axis, respectively. Abbreviations: nc, notochord; fp, floor plate; nt, neural tissue.|