Differential expression of angiogenic and anti-angiogenic molecules in the chick embryo chorioallantoic membrane and selected organs during embryonic development.

In this study we have investigated by real time polymerase chain reaction (RT-PCR) the expression of cytokines, which are well known angiogenic and anti-angiogenic molecules, during chick embryo development in four organs, namely the chorioallantoic membrane (CAM), heart, liver and optic tectum at four different stages. We have studied the expression of vascular endothelial growth factor-A (VEGF-A), fibroblast growth factor-2 (FGF-2), angiopoietin-1 (ANG-1), hypoxia inducible factor-1 and -2 alpha (HIF-1α and HIF-2α), hepatocyte growth factor (HGF), and of endostatin. All the pro-angiogenic cytokines examined showed a progressive increase in their expression in brain, heart, and liver, through all the stages of development, and parallel endostatin reduces its expression. In contrast, in the CAM, all the pro-angiogenic factors examined, with the exception of ANG-1, showed a stably-decreased expression during development, whereas endostatin progressively increased its expression. The CAM as an extraembryonic membrane which mediates gas and nutrient exchange until hatching, may be considered an outer organ and not an intrinsic organ of the developing embryo in which the mechanisms regulating the development of the vascular tree are different.