Endothelial Jag1 maintains arterial VSMC coverage in development and adulthood. (A-B) Representative images of vessels in P7 retinas from mice with (Jag1 lox/lox VECAD-Cre negative, “wild-type”) and without (Jag1 lox/lox VECAD-Cre positive, “JAG1 ECKO”) Jag1 in the endothelium. Retinas were immunostained with Abs to CD31 (red) and αSMA (green). (C-H) Large vessels from young adult mice were immunostained with Abs to CD31 (red), αSMA (green), and TOPRO (blue). Aorta from wild-type (C-D) and Jag1 ECKO (E-F) adult mouse. Arrows (F) indicate loss of smooth muscle cells in the layer immediately below the Jag1-negative endothelium. (G-H) Mesenteric vessel from Jag1 ECKO mouse, arrow (H) notes lack of smooth muscle cells. (I) Scale bars: (A-B) 100 μm; (C-F) 50 μm; and (G) 20 μm.