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. Author manuscript; available in PMC: 2017 Mar 1.
Published in final edited form as: Semin Cell Dev Biol. 2016 Feb 3;51:92–105. doi: 10.1016/j.semcdb.2016.02.001

Figure 1. Wnt, RA, and FGF pattern the foregut.

Figure 1

The primitive gut tube is regionalized along both A–P and D–V axes. During gastrulation, RA (red) is required for dorsal pancreas (DP; purple) specification, likely by inhibiting Shh expression. Slightly later, the foregut is distinguished from the hindgut by a gradient of Wnt signaling (orange). High posterior Wnt specifies the hindgut domain, while low anterior Wnt (yellow; limited by Sfrp5) signals through the Fzd7 receptor to promote foregut fates and initiate cellular morphogenesis. Finally, a gradient of FGF signaling from the neighboring cardiac/lateral plate mesoderm segregates ventral foregut organs; prolonged, higher levels of FGF are needed to specify liver (green) versus ventral pancreas (VP; blue).