Submitted March 1, 2006
Accepted August 9, 2006
Maturation and enucleation of primitive erythroblasts during mouse embryogenesis is accompanied by changes in cell surface antigen expression
Stuart T. Fraser, Joan Isern, and Margaret H. Baron*
Department of Medicine, Mount Sinai School of Medicine, New York, NY, USA
* Corresponding author; email: margaret.baron{at}mssm.edu.
Primitive erythroblasts (EryP) are the first hematopoietic cell type to form during mammalian embryogenesis and emerge within the blood islands of the yolk sac. Large, nucleated EryP begin to circulate around midgestation, when connections between yolk sac and embryonic vasculature mature. Two to three days later, small cells of the definitive erythroid lineage (EryD) begin to differentiate within the fetal liver and rapidly outnumber EryP in the circulation. The development and maturation of EryP remain poorly defined. Our analysis of embryonic blood at different stages reveals a stepwise developmental progression within the EryP lineage from E9.5 to E12.5. Thereafter, EryD are also present in the bloodstream and the two lineages are not easily distinguished. We have generated a transgenic mouse line in which the human 
-globin gene promoter drives expression of green fluorescent protein exclusively within the EryP lineage. Here we have used this line to characterize changes in cell morphology and surface marker expression as EryP mature and to track EryP numbers and enucleation throughout gestation. This study identifies previously unrecognized synchronous developmental stages leading to the maturation of EryP in the mouse embryo. Unexpectedly, we find that EryP are a stable cell population that persists through the end of gestation.
