Origin of endothelial cells from mesothelial-derived mesenchymal cells in the liver of avian embryos

We have tested the hypothesis of an origin of mesenchyme from the coelomic mesothelium of the developing avian liver and the differentiation of sinuso idal endothelial cells from mesothelial-derived mesenchymal cells. Our resu lts have shown that 1) Mesothelial cells of the developing liver and the su bmesothelial mesenchymal cells are simultaneously cytokeratin (CK) and vime ntin (VIM) immunoreactive between HH18 and HH28.2) A number of early sinuso idal cells are also CK immunoreactive. In the quail, CK colocalizes with th e vascular marker QH1 in these cells. 3) In late embryos (>HH30), only the mesothelium remains CK+. 4) Mesothelial and submesothelial mesenchymal cell s express the transcription factors Slug and WT1, both related to the epith elial-mesenchymal transition. 5) When the surface mesothelium was stained i n vivo with CCFSE, a carboxyfluorescein derivative, isolated sinusoidal cel ls were labelled after 24-48 h, These observations suggest that mesenchymal cells originate from the coelomic mesothelium of the developing liver and differentate into endothelial cells of the hepatic sinusoids.