Characterization of hemangioblast in umbilical arteries of mid-gestation mouse embryos.

Hemangioblasts are the common precursors of hematopoietic and vascular cells, and are characterized as blast colony-forming cells (BL-CFCs) in vitro. We previously identified BL-CFCs in the mouse aorta-gonads-mesonephros (AGM) region, but not yolk sac, placenta, circulation, or fetal liver. Here, we aim to determine whether BL-CFCs develop in the umbilical arteries (UA) that link the dorsal aorta (sub-region of AGM) and placenta. We find that the UA cells of E11.5 mouse embryos were capable of generating typical blast colonies. On replating, these colonies produced erythroid/myeloid progenitors and B220(+) B lymphocytes in vitro, corroborating their definitive hematopoietic nature. They also generated CD31(+) or endomucin(+) tube-like structures on OP9 stromal cells, showing their endothelial potential. The proximal and distal regions of UA had equal numbers of BL-CFCs. To evaluate whether BL-CFCs can be autonomously maintained or expanded in UA or AGM, in vitro organ culture was performed. Interestingly, the BL-CFC pool in the AGM was significantly amplified, in striking contrast to a decrease in the UA. Taken together, our findings indicate that in addition to the AGM the UA serves as an important, but less supportive, niche for hemangioblast development.