Abstract
Primitive erythroblasts are the first blood cells generated during embryonic hematopoiesis. Tracking their emergence both in vivo and in vitro has remained challenging due to the lack of specific cell surface markers. To selectively investigate primitive erythropoiesis, we have engineered a new transgenic embryonic stem (ES) cell line, where eGFP expression is driven by the regulatory sequences of the embryonic βH1 hemoglobin gene expressed specifically in primitive erythroid cells. Using this ES cell line, we observed that the first primitive erythroblasts are detected in vitro around day 1.5 of blast colony differentiation, within the cell population positive for the early hematopoietic progenitor marker CD41. Moreover, we establish that these eGFP+ cells emerge from a hemogenic endothelial cell population similarly to their definitive hematopoietic counterparts. We further generated a corresponding βH1-eGFP transgenic mouse model and demonstrated the presence of a primitive erythroid primed hemogenic endothelial cell population in the developing embryo. Taken together, our findings demonstrate that both in vivo and in vitro primitive erythrocytes are generated from hemogenic endothelial cells.
Highlights
Primitive erythroblasts are the first blood cells that are formed during embryogenesis[1]
In order to determine whether the expression of the βH1-eGFP reporter gene correlates with endogenous βH1 gene, transgenic embryonic stem (ES) clones were differentiated as embryoid bodies (EBs) for 7 days
These results indicate that the transgenic βH1-eGFP reporter ES cell line recapitulates the expression of endogenous βH1 and eGFP expression may be used to qualitatively track primitive erythropoiesis
Summary
Primitive erythroblasts are the first blood cells that are formed during embryogenesis[1]. Primitive erythroid (Ery/P) progenitors appear in the yolk sac blood islands around E7.253 within a first wave of hematopoiesis that generates macrophages and megakaryocytes[4, 5]. Human embryonic ε-globin gene promoter was coupled with jellyfish KGFP fluorescent protein[19] This mouse model was used to characterize the expression of cell surface markers by primitive erythrocytes between day 9.5 and 14.5 of embryogenesis as well as their enucleation. The same research group generated a second mouse model in which the fluorescent protein was replaced by H2B-EGFP fusion[20] This animal model was used to study primitive erythrocyte maturation within the fetal liver[20]. We hypothesized that βH1-globin, whose expression precedes that of the εy-globin gene[21] might represent a more suitable marker to track the onset of primitive erythropoiesis and to conclusively establish the cellular origin of primitive erythrocytes
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