ABSTRACT
In a series of discriminating experiments, the red cells of quail-chick embryo chimeras of various ages were harvested and separated according to species by differential immunohemolysis employing polyclonal antibodies against quail or chick erythrocytes. Subsequent construction of homospecific chick-chick chimeras eliminated the cited quantitative variability of the marked increase in circulating erythrocytes that were descendants of intraembryonic hemopoietic stem cells. A continuum of explorations employing the chick embryo chimera has led to the delineation of some specific, definitive features of the avian hemopoietic stem cell. It is established that the avian embryo has two populations of hemopoietic stem cells, one that is derived from precursor cells that arise in the yolk sac and another that has an intraembryonic origin. The hemopoietic stem cells that arise in the yolk sac are transitory blood cell progenitors that have a limited term existence and are incapable of long term renewal.
