In vitro studies on the existence of endothelial precursor cells in the subectodermal avascular region of quail wing buds.

In vitro studies were performed to investigate the angiogenic capacity of different parts of the avian limb bud. Small pieces of wing mesenchyme of the vascularized core or of the avascular subectodermal region were obtained from quail embryos at stages 18 to 25, and were cultured. The identification of the avascular wing mesenchyme was made possible after injection of India ink via the vitelline vein or by bleeding control during in vivo dissection. Tissue cultures were treated with the QH-1 antibody or/and the endothelial cell marker DiI-Ac-LDL. Endothelial cells were found in cultures of the mesenchymal core and in those of the avascular subectodermal wing mesenchyme. Moreover, their appearance was independent of the stage of the donor embryo. Although there were no vessels, the subectodermal wing mesenchyme was able to produce endothelial cells that proliferated and differentiated under in vitro conditions. Thus, endothelial precursor cells probably existed within the avascular wing mesenchyme. These cells might be identical with the QH-1-positive isolated cells that have been described in immunohistochemical studies of this region; they may contribute to the growing capillary plexus of the limb bud.