Fig. 5.

Heterozygotes are defective in sustaining large vessels. (A) Vessel size distribution varied between wild-type and heterozygous mouse tumors. Tumors in wild-type mice bore more large vessels than tumors in heterozygous mice, and exhibited more variation in vessel size distribution. (B) Wild-type mice exhibited significantly more large (10,000–20,000) and extra large (>20,000) vessels than heterozygotes (P < 0.01 and P < 0.0001, respectively). Inset shows a representative tumor section from a wild-type and heterozygous mouse, stained for CD31. (C) Tumor sections were stained for αSMA (red), cleaved caspase-3 (green), and DAPI (blue). (a and b) Compared to wild-type mice (a), tumors from heterozygous mice (b arrows) exhibited more large vessels with discontinuous αSMA staining, indicating a loss of pericytes. (c and d) However, small vessels of both wild-type (c) and heterozygous (d) mice were well-encompassed by a continuous layer of αSMA-positive cells. There was no cleaved caspase-3 staining in endothelial cells or pericytes. Red blood cells exhibited slight background staining. (D) The absence of large vessels caused a significant decrease in overall luminal area. We show that wild-type and heterozygous tumors are composed of 4.0% and 2.6% vascular space, respectively (P < 0.0005; Student's t test). Additionally, large vessels account for 70% of the vascular space in wild-type tumors, compared with only 48% in heterozygous tumors. This indicates that wild-type tumors rely heavily on large vessels for their rapid growth.