Fig. 8. A model of Wnt/ß-catenin-mediated endoderm patterning in Xenopus. Schematic showing an early-somite stage Xenopus embryo. Canonical Wnts secreted from the mesoderm (orange) signal to the adjacent posterior endoderm (yellow) to repress foregut development by activating the homeodomain repressor Vent2, which in turn inhibits the expression of key foregut genes such as hhex and foxa2 in the posterior endoderm. The anterior endoderm (green) secretes a number of Wnt-antagonists that block the Wnt signals from the mesoderm, allowing hhex and foxa2 expression to impart foregut identity. The hhex-expressing anterior endoderm then sends an unknown signal to the adjacent mesoderm inducing it to become cardiac. Later in development, the cardiogenic mesoderm signals back to the endoderm (curved dashed line), inducing a subset of the foregut endoderm to adopt a hepatic fate.