DLL4 is expressed by pericytes/vascular smooth muscle cells in Ewing's sarcoma and was found to be important for formation of the perivascular cell layer. For this image, subcutaneous Ewing's sarcoma tumors from nude mice were harvested and examined by immunohistochemistry for DLL4 (green) and the pericyte/vascular smooth muscle cell marker α-SMA (red). DLL4, α-SMA double positive cells are yellow or orange. Hoescht 33342 was used to visualize nuclei (blue). For details, see the article by Schadler and colleagues on page 848 of this issue.