Expression of the hyaluronan receptor LYVE-1 is not restricted to the lymphatic vasculature; LYVE-1 is also expressed on embryonic blood vessels.

Expression of the hyaluronan receptor LYVE-1 is one of few available criteria used to discriminate lymphatic vessels from blood vessels. Until now, endothelial LYVE-1 expression was reported to be restricted to lymphatic vessels and to lymph node, liver, and spleen sinuses. Here, we provide the first evidence that LYVE-1 is expressed on blood vessels of the yolk sac during mouse embryogenesis. LYVE-1 is ubiquitously expressed in the yolk sac capillary plexus at E9.5, then becomes progressively down-regulated on arterial endothelium during vascular remodelling. LYVE-1 is also expressed on intra-embryonic arterial and venous endothelium at early embryonic stages and on endothelial cells of the lung and endocardium throughout embryogenesis. These findings have important implications for the use of LYVE-1 as a specific marker of the lymphatic vasculature during embryogenesis and neo-lymphangiogenesis. Our data are also the first demonstration, to our knowledge, that the mouse yolk sac is devoid of lymphatic vessels.