Fig. 8. The serosal mesothelium gives rise to mural cells of gut vasculature. (Left) At E9.5, the embryonic gut is not covered by a mesothelium. The gut consists only of endoderm (e) and splanchnic mesoderm (splm). A vascular plexus (red) runs between endoderm and splanchnic mesoderm, and within the mesentery. (Center) At E10.5, the Wt1/Cytokeratin-positive serosal mesothelium (green) starts to cover the mesentery and, subsequently, by E11.5, coats the entire gut. (Right) Serosal mesothelial cells undergo EMT into the subserosal space, where these mesenchymal cells discontinue Wt1 expression (open green triangles). (Box) Progeny of the serosal mesothelial cells differentiate into smooth muscle cells surrounding the blood vessels (red) that form in the subserosal space. A subset of these progeny differentiates into, as yet unidentified, non-vessel cells (triangle with question mark). da, dorsal aorta.