19 Review for lymphatic development, and that the blood vascular and lymphatic systems subsequently employ distinct regulatory proteins. Podoplanin, an integral membrane protein first found in glomerular epithelial cells, has also been shown to be specifically expressed in the endothelium of lymphatic capillaries, but not in the blood vasculature15. In the skin and kidney vasculature, podoplanin colocalized with VEGFR-3, and all endothelial cells of Kaposi’s sarcomas expressed both VEGFR-3 and podoplanin, thus mimicking cells of lymphatic endothelial origin15, 16. LYVE-1, a CD44 homologue, has recently been identified as a receptor for the extracellular matrix glycosaminoglycan hyaluronan. LYVE-1 colocalizes with hyaluronan on the luminal surface of the lymph vessel wall and is completely absent from blood vessels17. Although the specific roles of Prox1, podoplanin and LYVE-1 in lymphatic endothelial cell functions are yet to be defined, these markers can now be used to study the lymphatic development and to explore the etiology of lymphatic diseases.