DEVELOPMENT OF HEMATOPOIETIC STEM-CELL ACTIVITY IN THE MOUSE EMBRYO

The precise time of appearance of the first hematopoietic stem cell ac tivity in the developing mouse embryo is unknown. Recently the aorta-g onad-mesonephros region of the developing mouse embryo has been shown to possess hematopoietic colony-forming activity (CFU-S) in irradiated recipient mice. To determine whether the mouse embryo possesses defin itive hematopoietic stem cell activity in the analogous AGM region and to determine the order of appearance of stem cells in the yolk sac, A GM region, and liver, we transferred these embryonic tissues into adul t irradiated recipients. We report here the long-term, complete, and f unctional hematopoietic repopulation of primary and serial recipients with AGM-derived cells. We observe potent hematopoietic stem cell acti vity in the AGM region before the appearance of yolk sac and liver ste m cell activity and discuss a model for the maturation of stem cell ac tivity in mouse embryogenesis.