Effect of erythroid Vegf overexpression on vasculature and environment. (A) E9.5 yolk sac Pecam (left) vessel and Caspase-3 (right) apoptosis immunohistochemistry staining analysis (magnifications, 200×). (B) Relative mRNA levels of key growth factor receptors and ligands measured by q-RT-PCR in E8.5 yolk sacs. Bars represent mean ± SEM; *P < .05, **P < .01.