Fig. 2. Tie1-Cre-mediated lacZ expression in R26R mice. By crossing Tie1-Cre and R26R reporter mice, the expression and efficiency of the Cre recombinase could be studied. These crossings also contained the Pdgfb conditional and null alleles. Sections are stained for ß-gal (blue) and are counterstained with Erythrosin (pink). (A) An overview section of the kidney cortex shows a lacZ expression pattern compatible with vascular expression. g, glomerulus; a, artery; cap, capillary. (B,C) Glomerular endothelial expression is evident at higher magnification. (D,E) Peritubular capillary endothelium is largely but not homogenously ß-gal-positive (arrowheads). (F-L) In the heart and its large vascular connections, the endocardium, the cardiac valves and endothelium are ß-gal positive, albeit not at 100% (arrow in J indicates an unstained endothelial cell). Deep in the myocardium, the capillaries are the only ß-gal-positive structures (H). The endothelium of the large vessels, here illustrated by the aortic arch (F), show a chimeric Cre expression (K,L; boxed regions in F at higher magnification). (M) The placenta vessels that are lined by a ß-gal-stained endothelium (green, arrowheads) could be classified as fetal by their content of large immature erythrocytes. (N) Diagrammatic representation of M, showing maternal sinuses (red) and fetal vessels (blue). Scale bars: 10 µm in A-E,H-L; 100 µm in F,G,M.