Induction of vasculogenesis in quail blastodisc-derived embryoid bodies.

We have previously developed an in vitro culture system in which dissociated cells from unincubated quail blastodiscs formed in vivo-like blood islands consisting of blood and endothelial cells in response to fibroblast growth factors (FGFs). Here we demonstrate that the same quail blastodisc cells grown in suspension culture in the presence of basic FGF (bFGF) reaggregated and formed three-dimensional spherules (embryoid bodies, EBs) which underwent vasculogenesis and hematopoiesis within 3 days. In contrast to murine embryoid bodies, which undergo vasculogenesis spontaneously, the formation of vascular structures in quail blastodisc cultures was absolutely dependent on bFGF. While about 75% contained blood islands and about 50% formed capillaries in the presence of bFGF, only 0.2% of the embryoid bodies formed blood islands in control cultures without bFGF. Vascular channels were gradually encoated by primitive smooth muscle cells within 5 days. Ultrastructural examinations revealed capillary blood vessels and blood islands indistinguishable from their yolk sac counterparts. Mesodermal tissue was present in cultures both with and without bFGF, but consisted of an avascular undifferentiated mesenchyme in control cultures. Since the entire sequence of vasculogenesis from the formation of endothelial cells to their assembly into a vascular plexus is observed in response to the inducer bFGF, this culture system is a suitable model for studying the molecular events that initiate the emergence of endothelial cells and the formation of a vascular plexus during vasculogenesis.