[Identification, emergence and mobilization of circulating endothelial cells in the embryo]

Using quail-chick parabiosis and the QH1 monoclonal antibody, specific for the endothelial and hematopoietic cells of the quail species, as a marker, we identified circulating endothelial cells in the embryo. In normal conditions, these cells could integrate endothelia in many tissues but their number remained low. When artificial angiogenic responses were created, i.e., in grafting experiments on the chorioallantoic membrane or wound healing, the circulating endothelial cells were rapidly mobilized to reach the embryonic regions submitted to these processes and their number dramatically increased. Interestingly, 1) on one hand, these circulating endothelial cells were present early in ontogeny, before the third embryonic day in the quail embryo; 2) on the other hand, their mobilization was not dependent on the presence of the bone marrow since it was effective before the differentiation of this tissue.