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. Author manuscript; available in PMC: 2010 Feb 1.
Published in final edited form as: Bioessays. 2009 Feb;31(2):139–152. doi: 10.1002/bies.200800123

Figure 2. Model of endoderm regionalization.

Figure 2

A) Retinoic Acid (RA) is required between 8–13 hpf to specify the pancreas. RA is synthesized in the paraxial mesoderm by raldh2. Endodermal expression of the cdx4 transcription factor prevents posterior endoderm from expressing insulin. The β-cells are located anterior to the domain of high cdx4 expression. B) Opposing gradients of Retinoic Acid (RA) and cdx4 limit insulin expression to the foregut. The posterior limit of the pancreas is set by cdx4. Endodermal factors that limit the anterior boundary of the pancreas have not been identified.