Expression of pro- and anti-angiogenic factors during the formation of the periocular vasculature and development of the avian cornea.

BACKGROUND: During embryonic development, endothelial precursor cells (angioblasts) migrate relatively long distances to form the primary vascular plexus. The migratory behavior of angioblasts and localization of the primitive blood vessels is tightly regulated by pro-angiogenic and anti-angiogenic factors encountered in the embryonic environment. Despite the importance of corneal avascularity to proper vision, it is not known when avascularity is established in the developing cornea and how pro- and anti-angiogenic factors regulate this process. RESULTS AND DISCUSSION: Using Tg(tie1:H2B:eYFP) transgenic quail embryos to visualize fluorescently labeled angioblasts, we show that the presumptive cornea remains avascular despite the invasion of cells from the periocular region where migratory angioblasts reside and form the primary vasculature. Semiquantitative reverse transcriptase polymerase chain reaction analysis and spatiotemporal examination of gene expression revealed that pro- and anti-angiogenic factors were expressed in patterns indicating their potential roles in angioblast guidance.
CONCLUSIONS: Our findings show for the first time that chick corneal avascularity is established and maintained during development as the periocular vasculature forms. We also identify potential candidate pro- and anti-angiogenic factors that may play crucial roles during vascular patterning in the anterior eye.