CFU-S11 activity does not localize solely with the aorta in the aorta-gonad-mesonephros region

Abstract

The aorta-gonad-mesonephros (AGM) region is a potent hematopoietic site in the midgestation mouse conceptus and first contains colony-forming units–spleen day 11 (CFU-S11) at embryonic day 10 (E10). Because CFU-S11 activity is present in the AGM region before the onset of hematopoietic stem cell (HSC) activity, CFU-S11 activity in the complex developing vascular and urogenital regions of the AGM was localized. From E10 onward, CFU-S11 activity is associated with the aortic vasculature, and is found also in the urogenital ridges (UGRs). Together with data obtained from organ explant cultures, in which up to a 16-fold increase in CFU-S11 activity was observed, it was determined that CFU-S11 can be increased autonomously both in vascular sites and in UGRs. Furthermore, CFU-S11 activity is present in vitelline and umbilical vessels. This, together with the presence of CFU-S11 in the UGRs 2 days before HSC activity, suggests both temporally and spatially distinct emergent sources of CFU-S11.