Fig. 2. Blood vessel formation in mesentery and gut. (A) Pecam is expressed in the endodermally associated plexus in the gut tube and mesentery (A, arrowheads) at E11.5. No surface staining is observed. (B) At E13.5, Pecam-positive cells are seen on the surface of the gut (arrows), connecting to the plexus via endothelial bridges (arrowhead). (C) At this time, no vascular smooth muscle cells are detected on the gut surface by anti-SMA staining; however, visceral muscle (vism) is detected. (D,E) In later stages, smooth muscle is associated with developing endothelial tubes in the mesentery and gut tube. e, endoderm; lua, left umbilical artery. Scale bars: 100 µm in A; 50 µm in B-E.