CHARACTERIZATION OF THE FIRST DEFINITIVE HEMATOPOIETIC STEM-CELLS IN THE AGM AND LIVER OF THE MOUSE EMBRYO

At day 10 in mouse gestation, the intraembryonic aorta-gonads-mesoneph ros (AGM) region generates the first definitive hematopoietic stem cel ls (HSCs) of the adult blood system. By 11 days postcoitum, the liver contains such HSCs. While HSCs of the adult bone marrow and late-stage fetal liver have been extensively characterized for cell surface mark ers, there has been no phenotypic description of the first HSCs during embryo development. We report here the temporal cell surface phenotyp e of HSCs from the AGM region and early fetal liver and show that all HSCs reside in the c-kit(+) population. c-kit(+) HSCs from AGM and liv er are mainly CD34(+) and in the AGM are in both Mac-1(+) and Mac-1 fr actions. These results demonstrate that during mouse ontogeny the firs t definitive HSCs are similar in cell surface phenotype to the HSCs of adult bone marrow but that spatial localization and developmental tim e are critical factors in the phenotypic assessment of this functional cell population.