Up regulation of TAL-1, its VE-Cadherin target gene and Angiopoietin-2 in tumor vessels of Lyl1 -deficient mice. (A) Endothelial Tal-1 expression in LLC tumors implanted in Δ^Lyl1/Δ^Lyl1, WT/Δ^Lyl1 and WT mice. (Left) Total RNA was extracted from 1 or 2 pieces of tumors from mice of the 3 genotypes. Each point represents data for distinct piece of tumors: Δ^Lyl1/Δ^Lyl1 (14 pieces/9 tumors); WT/Δ^Lyl1 (7 pieces/5 tumors); WT (8 pieces/6 tumors). cDNAs were amplified in triplicate by specific Tal-1. Shown are normalized Tal-1 mRNA levels relative to CD31 mRNA levels (see supplemental Figure 1B) in each piece of tumor. The mean is represented as a black bar on this scatter plot. **P < .01; *P < .05. (Right) Immunofluorescence analysis of TAL-1 protein in LLC tumors from WT and Δ^Lyl1/Δ^Lyl1 mice. Representative microscopy images showing TAL-1 expression in the nucleus of endothelial cells boarding a blood vessel in a tumor of Δ^Lyl1/Δ^Lyl1 mice (white arrows), but not in tumor of their WT littermates. Tumor sections were double-stained for TAL-1 (red) and for blood vessel marker CD31 (green). Scale bar: 20 μm. (Bottom) TAL-1 expression in immature erythroid cells WT mice used here as positive control for TAL-1 staining. Spleen sections were double-stained for TAL-1 (red) and for the macrophage marker CD11b/CD18 (Mac1, green). Note the specific intense TAL-1 staining in the large nuclei of blast cells, but not in the smaller nuclei of lymphocytes or macrophages. Scale bar: 20 μm. (B) Total RNA was extracted from 1 or 2 pieces of tumors from mice of the 3 genotypes (as in panel A). cDNAs were amplified in triplicate by specific VE-cadherin or Ang-2 primers. VE-cadherin and Ang-2 mRNA levels were normalized to beta-Actin. Each bar is the mean ± SD of mRNA levels relative to mRNA levels of WT mice-derived, set arbitrarily at 1 ***P < .005; **P < .01