Barrier function of the coelomic epithelium in the developing pancreas.

Tight spatial regulation of extracellular morphogen signaling within the close confines of a developing embryo is critical for proper organogenesis. Given the complexity of extracellular signaling in developing organs, together with the proximity of adjacent organs that use disparate signaling pathways, we postulated that a physical barrier to signaling may exist between organs in the embryo. Here we describe a previously unrecognized role for the embryonic coelomic epithelium in providing a physical barrier to contain morphogenic signaling in the developing mouse pancreas. This layer of cells appears to function both to contain key factors required for pancreatic epithelial differentiation, and to prevent fusion of adjacent organs during critical developmental windows. During early foregut development, this barrier appears to play a role in preventing splenic anlage-derived activin signaling from inducing intestinalization of the pancreas-specified epithelium.