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Signaling by the Wnt family of secreted growth factors is involved in numerous different aspects of embryonic development and also for maintenance of cellular function in adult tissues. In addition to regulation at the transcriptional level, Wnt activity is modulated by a number of different Wnt-binding proteins. Here we report the cloning and developmental expression pattern of the Xenopus orthologue of secreted Frizzled-related protein 5 (sFRP5), an endogenous inhibitor of Wnt signaling. At early stages of endodermal differentiation, sFRP5 is expressed in the developing liver. At later stages however, sFRP5 expression is down-regulated in the liver and becomes strongly expressed in the region corresponding to the junction between the posterior portion of the stomach and the anterior intestines.
Fig. 2. Developmental expression of Xenopus sFRP5. In situ hybridization of whole-mount embryos (A, B, E, H); transverse sections (C, F); and whole dissected gut tubes (I–O) shows sFRP5 expression in endodermal structures. (A) Lateral; and (B) ventro-lateral views of a stage 25 embryo show expression of sFRP5 in endoderm in a region overlapping the developing liver. (E) This domain of expression persists in the stage 34 embryo. (C, F) Transverse sections through stages 25 and 34 embryos, respectively, reveal sFRP5 expression throughout the endodermal layer of the liverprimordium. (D, G) Staining using the liver marker Hex at stages 25 and 34 respectively. (H) By stage 39, sFRP5 is absent from the liver but present in endodermal tissues posterior and dorsal to the liver. White arrowhead marks endodermposterior to the liver. (I, J) Lateral view and ventral view respectively of dissected stage 41 gut tube showing strong sFRP5 expression in the posterior region of the stomach and weaker expression in the anterior portion of the intestines. The black arrowhead points to the anterior boundary of sFRP5 expression in the stomach and the brackets indicate the domain of expression in the intestines. Note that expression is absent from liver and pancreas at this stage. (K) Dissected stage 46 gut tube showing maintenance of posteriorstomach/anteriorintestine expression pattern. Arrow head marks anterior domain of sFRP5 expression in stomach and bracket indicates domain of expression in intestines. (L) Lateral view of dissected stage 41 gut tube, showing expression of the stomach marker, Sox2, that is expressed throughout the entire stomachepithelium. (M). Sox2 expression in a dissected stage 46 gut tube. (N) Lateral view of dissected stage 41 gut tube showing expression of Cad2, which marks the entire length of the intestines. (O) Cad2 expression in a dissected stage 46 gut tube. For all gut tube images, anterior is to the left. Li, liver; Pa, pancreas.
