AN AVIAN MODEL FOR STUDIES OF EMBRYONIC LYMPHANGIOGENESIS

Abstract

Embryonic development of lymphatics (lymphangiogenesis) in recent years has rarely beenstudied experimentally. Using an avian model, we showed that both intra- and extra-embryonicblood vessels of chick and quail embryos are accompanied by lymphatics. The lymphatics of thechorioallantoic membrane (CAM) are drained by lymphatic trunks of the umbilicus and areconnected to the posterior lymph hearts. Intra-embryonic lymphatics are drained via pairedthoracic ducts into the jugulo-subclavian junction. The lymphatic endothelial cells arecharacterized by the expression of Vascular Endothelial Growth Factor Receptors (VEGFR) -2and -3. Application of VEGF-C, the ligand of these two receptors, on the differentiated CAM,induces proliferation of lymphatic endothelial cells and formation of huge lymphatic sinuses.These lymphatics derive from pre-existing lymphatic endothelial cells, whereas, in early embryoslymphangioblasts are present in the mesenchyme. This phenomenon can be demonstrated byinterspecific grafting experiments between chick and quail embryos. Together with the earlylymph sacs, the lymphangioblasts form the embryonic lymphatic system. Our studies demonstratethe importance of lymphangioblasts and lymphangiogenic growth factors in embryoniclymphangiogenesis.