title: Development of the avian lymphatic system.
abstract: Recently, highly specific markers of the lymphatic endothelium have been found enabling us to reinvestigate the embryonic origin of the lymphatics. Here we present a review of our studies on the development of the lymphatic system in chick and quail embryos. We show that the lymphatic endothelium is derived from two sources: the embryonic lymph sacs and mesenchymal lymphangioblasts. Proliferation studies reveal a BrdU-labeling index of 11.5% of lymph sac endothelial cells by day 6.25, which drops to 3.5% by day 7. Lymphangioblasts are able to integrate into the lining of lymph sacs. Lymphatic endothelial cells express the vascular endothelial growth factor (VEGF) receptors-2 and -3. Their ligand, VEGF-C, is expressed almost ubiquitously in embryonic and fetal tissues. Elevated expression levels are found in the tunica media of large blood vessels, which usually serve as major routes for growing lymphatics. The homeobox gene, Prox1, is expressed in lymphatic but not in blood vascular endothelial cells throughout all stages examined, namely, in developing lymph sacs of day 6 embryos and in lymphatics at day 16. Experimental studies show the existence of lymphangioblasts in the mesoderm, a considerable time before the development of the lymph sacs. Lymphangioblasts migrate from the somites into the somatopleure and contribute to the lymphatics of the limbs. Our studies indicate that these lymphangioblasts already express Prox1.
authors.affiliation: Anatomisches Institut der Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany. wilting@uni-freiburg.de
authors.forename: J
authors.initials: J
authors.lastname: Wilting
authors.forename: M
authors.initials: M
authors.lastname: Papoutsi
authors.forename: K
authors.initials: K
authors.lastname: Othman-Hassan
authors.forename: M
authors.initials: M
authors.lastname: Rodriguez-Niedenführ
authors.forename: F
authors.initials: F
authors.lastname: Pröls
authors.forename: S I
authors.initials: SI
authors.lastname: Tomarev
authors.forename: A
authors.initials: A
authors.lastname: Eichmann
mesh_terms: D000818:Animals; D001717:Birds / Q000196:embryology*; D002642:Chick Embryo; D016228:Endothelial Growth Factors / Q000032:analysis; D004729:Endothelium, Lymphatic / Q000196:embryology / Q000378:metabolism; D018398:Homeodomain Proteins / Q000032:analysis / Q000276:immunology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008208:Lymphatic System / Q000098:blood supply / Q000196:embryology*; D011784:Quail / Q000196:embryology; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis; D017978:Receptors, Growth Factor / Q000032:analysis; D040262:Receptors, Vascular Endothelial Growth Factor; D025521:Tumor Suppressor Proteins; D042582:Vascular Endothelial Growth Factor C; D000098551:Prospero-Related Homeobox 1 Protein
chemical_list: D016228:Endothelial Growth Factors; D018398:Homeodomain Proteins; D017978:Receptors, Growth Factor; D025521:Tumor Suppressor Proteins; D042582:Vascular Endothelial Growth Factor C; D000098551:Prospero-Related Homeobox 1 Protein; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor