Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
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.
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.
