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The transcription factors Mixer and Sox17beta have well-characterized roles in endoderm specification during Xenopus embryogenesis. In order to more thoroughly understand the mechanisms by which these endodermal regulators act, we expressed Mixer and Sox17beta in naïve ectodermal tissue and, using oligonucleotide-based microarrays, compared their genomic transcriptional profile to that of unaffected tissue. Using this approach, we identified 71 transcripts that are upregulated by Mixer or Sox17beta, 63 of which have previously uncharacterized roles in endoderm development. Furthermore, an in situ hybridization screen using antisense probes for several of these clones identified six targets of Mixer and/or Sox17beta that are expressed in the endoderm during gastrula stages, providing new and regional markers of the endoderm. Our results contribute further insight into the functions of Mixer and Sox17beta and bring us closer to understanding at the molecular level the pathways that regulate endoderm development.
Figure 2. In situ hybridization screen reveals new expression patterns. A: Embryos at gastrula (10.5), neurula (15), and tailbud (30) stage are stained with antisense (left) and sense (right) probes for EST-11 showing expression in the mesoderm, neural tube, neural crest, and pronephros. B: Embryos at neurula and tailbud stage are stained with antisense and sense probes for EST-10 demonstrating expression in cement gland, neural tube nasal placode, otic placod, and forebrain. C: Embryos at gastrula and tailbud stage are stained for antisense and sense probes for EST-14 demonstrating expression in mesoderm and in a single posteriorsomite. D: Embryos at neurula and tailbud stage are stained with antisense and sense probes for EST-8, indicating expression within forebrain and heart. E: Embryos at neurula and tailbud stage are stained with antisense and sense probes for EST-34, showing expression in the placodes. F: Embryos at tailbud stage are stained with antisense and sense probes for EST-28 showing expression in nasal placodes and hindbrain. G: Embryos at neurula stage are stained with antisense and sense probes for EST-19, indicating expression within the neural tube. H: Embryos at tailbud stage are stained with antisense and sense probes for EST-9, demonstrating expression within pronephros and neural crest.
Figure 3. Six transcripts are expressed in the early endoderm. The first two columns display stage 10.5 embryos, vegetal view, stained with antisense and sense probes for Cxcr4, March8, Borg4, EST-21, Gpr-4, and Xtwik-2. The last two columns display hemisected stage 10.5 embryos, lateral view, stained with antisense and sense probes for the same transcripts above. The descriptions along the right side indicate which transcripts were upregulated with either Mixer, Sox17 beta , or both. The arrow points to the deeper cells adjacent to the blastopore ring expressing March8.
Figure 4. EST-21 and Gpr-4 have additional patterns during later embryonic stages. A,B: Embryos at tailbud stage are stained with antisense and sense probes for EST-21. C,D: Neurula stage embryos are stained with antisense and sense probes for Gpr-4. E,F: Tailbud stage embryos are stained with antisense and sense probes for Gpr-4.
Fig. 2. Sp8 expression at stg. 30
Fig. 4. Grp-4 expression at tailbud stg.
fig. 2. Pcdh10 expression at stg 22-44
Fig. 2. Btg4-a expression at tailbud stage
Fig. 5. RT-PCR analysis confirms array data and supports an endogenous role for six new
molecules in the endoderm pathway. RT-PCR was performed on cDNA synthesized from ectoderm
explants expressing Mixer, Sox17 , Smad2, or VegT with primers for Cxcr4, March8, Borg4,
EST-21, Gpr-4, and Xtwik-2. -gal was injected as a control. Primers for Sox17 and Xbra were
used as positive controls. ODC was used as a loading control. WE, whole embryo; RT, minus
reverse transcriptase.
loc100492494 (fish-egg lectin-like) gene expression in bissected Xenopus laevis embryo, assayed via in situ hybridization, NF stage 10.5, horizontal view.
loc100492494 (fish-egg lectin-like) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 26, lateral view, anteriorleft, dorsal up.
plk2 (polo-like kinase 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 28, lateral view, anteriorleft, dorsal up.
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