Fig. 3. The endoderm is a direct target of ß-catenin signaling. (A) Experimental design of the endoderm transplantations. Anterior endoderm (AE) or posterior endoderm (PE) was dissected from gastrula Xenopus embryos injected with RNA encoding GFP, pt-ß-catenin+GFP or Gsk3ß and GFP and the tissue was transplanted into the bastocoel of uninjected sibling host embryos. (B,C) Confocal analysis at the neurula stage indicates that the GFP-labeled cells were incorporated into the host endoderm near the presumptive midgut. (D-G) At stage 42, control AE transplants (D) contributed primarily to liver (li) and foregut, whereas control PE transplants (E) mostly contributed to the intestine (i). By contrast, AE injected with pt-ß-catenin (F) rarely contributed to foregut, whereas PE injected with Gsk3ß (G) frequently contributed to the liver. GFP-labeled cells were only observed in the endoderm and not the heart (h) or other mesoderm tissue. (H) Bar chart showing the location frequency of each type of transplant.