CFU-S-11 activity does not localize solely with the aorta in the aorta-gonad-mesonephros region

The aorta-gonad-mesonephros (AGM) region is a potent hematopoietic site in the midgestation mouse conceptus and first contains colony-forming units-sp leen day II (CFU-S-11) at embryonic day 10 (E10), Because CFU-S-11 activity is present in the AGM region before the onset of hematopoietic stem cell ( HSC) activity, CFU-S-11 activity in the complex developing vascular and uro genital regions of the AGM was localized. From E10 onward, CFU-S-11 activit y is associated with the aortic vasculature, and is found also in the uroge nital ridges (UGRs), Together with data obtained from organ explant culture s, in which up to a 16-fold increase in CFU-S-11 activity was observed, it was determined that CFU-SH can be increased autonomously both in vascular s ites and in UGRs, Furthermore, CFU-S-11 activity present in vitelline and u mbilical vessels. This, together with the presence of CFU-S-11 in the UGRs 2 days before HSC activity, suggests both temporally and spatially distinct emergent sources of CFU-S-11. (C) 2000 by The American Society of Hematolo gy.