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Xenopus cDNA microarray identification of genes with endodermal organ expression

ABSTRACT: The endoderm is classically defined as the innermost layer of three Metazoan germ layers. During organogenesis, the endoderm gives rise to the digestive and respiratory tracts as well as associated organs such as the liver, pancreas, and lung. At present, however, how the endoderm forms the variety of cell types of digestive and respiratory tracts as well as the budding organs is not well understood. In order to investigate the molecular basis and mechanism of organogenesis and to identify the endodermal organ-related marker genes, we carried out microarray analysis using Xenopus cDNA chips. To achieve this goal, we isolated the Xenopus gut endoderm from three different stages of Xenopus organogenesis, and separated each stage of gut endoderm into anterior and posterior region. Competitive hybridization of cDNA between the anterior and posterior endoderm regions, to screen genes that specifically expressed in the major anterior organs, revealed 891 candidates. We then selected 104 clones for in situ hybridization analysis. Here, we report the identification and expression patterns of the 104 Xenopus endodermal genes, which would serve as useful markers for studying endodermal organ development. Keywords: Xenopus, endoderm, microarray, organogenesis

ORGANISM(S): Xenopus laevis

PROVIDER: GSE7129 | GEO | 2007/03/31

SECONDARY ACCESSION(S): PRJNA98213

REPOSITORIES: GEO

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Project description:In Xenopus, establishment of the anterior-posterior axis involves two key signalling pathways, canonical Wnt and Nodal-related TGF-Î². There are also a number of transcription factors that feedback upon these pathways. The homeodomain protein Hex, an early marker of anterior positional information, acts as a transcriptional repressor suppressing induction and propagation of the Spemman organiser while specifying anterior identity. We show that Hex promotes anterior identity by amplifying the activity of canonical Wnt signalling. Hex exerts this activity by inhibiting the expression of Tle-4, a member of the Groucho family of transcriptional co-repressors that we identified as a Hex target in embryonic stem (ES) cells and Xenopus embryos. This Hex-mediated enhancement of Wnt signalling results in the up-regulation of the Nieuwkoop centre genes Siamois and Xnr-3 and the subsequent increased expression of the anterior endodermal marker Cerberus and other mesendodermal genes downstream of Wnt signalling. We also identified Nodal as a Hex target in ES cells. We demonstrate that in Xenopus, the Nodal-related genes Xnr-1 and 2, but not 5 and 6, are regulated directly by Hex. The identification of Nodal-related genes as Hex targets explains the ability of Hex to suppress induction and propagation of the organiser. Together these results support a model in which Hex acts early in development to reinforce a Wnt-mediated, Nieuwkoop-like signal to induce anterior endoderm, and later in this tissue to block further propagation of Nodal-related signals. The ability of Hex to regulate the same targets in both Xenopus and mouse implies this model is conserved. Experiment Overall Design: Identification of Hex target genes In Xenopus, the establishment of the anterior-posterior axis involves two key signalling pathways, the canonical Wnt and the Nodal-related TGF-Î² and a number of transcription factors that feedback upon these pathways. The homeodomain protein Hex, an early marker of anterior positional information, is a transcriptional repressor that suppresses the induction and propagation of the Spemman organiser while specifying anterior identity. Using microarray expression profiling we identified mouse Tle-4 as a Hex target in Embryonic Stem (ES) cells and showed that Tle-4 expression is directly regulated by Hex in Xenopus embryos. We also identified Nodal as a Hex target in ES cells. Taken together these results support a model in which Hex acts early in development to reinforce a Wnt-mediated, Nieuwkoop-like signal to induce anterior endoderm and later in this tissue to block further propagation of Nodal-related signals. The ability of Hex to regulate the same targets in both frog and mouse suggests that this model is conserved.

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Xenopus cDNA microarray identification of genes with endodermal organ expression

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