| Primitive erythroblasts (EryP) form in the yolk sac of the mouse embryo and then enter the circulation, where they undergo a stepwise morphological progression. They complete their maturation in the fetal liver and enucleate. I have evaluated a series of transgenic embryonic stem cell lines in which a fluorescent (GFP) reporter is expressed exclusively within EryP as an in vitro system for studying primitive erythropoiesis. During differentiation of these cells, GFP was expressed transiently with kinetics that coincided with production of red hemoglobin pigmentation. The GFP+ cells were isolated by FACS and observed to be very similar to mouse yolk sac erythroblasts on the basis of morphology, Giemsa staining, expression of endogenous embryonic beta-like globin genes and surface antigens. EryP maturation in vitro recapitulated only very early circulation stage development, possibly due to the absence of microenvironmental signals present in the embryo. |
