[Hematopoietic potential of Flk-1(+) populations in mouse embryonic AGM region]

This study aimed to investigate the expression of Flk-1 on distinct hematopoietic precursor cells in E10.5 mouse AGM region. By flow cytometry, we found that < 10% of Flk-1(+) cells of E10.5 AGM region co-expressed CD41 and CD45/Ter119. Then, E10.5 AGM cells were fractionated into two subsets, the CD31(+)CD45(-)Ter119(-)Flk-1(+)CD41(+) cells (R1, putative immature hematopoietic cells) and the CD31(+)CD45(-)Ter119(-)Flk-1(+)CD41(-) cells (R2, putative endothelial cells), followed by methylcellulose-based CFU-C assay and OP9-based stromal co-culture to examine their myeloid or/and lymphoid potential in vitro. The results showed that only R1 cells could give rise to typical hematopoietic colonies in CFU-C assay. In contrast, after co-cultured with OP9 for 7-9 days, both subsets could generate abundant hematopoietic progenitor cells (CD45(+)c-Kit(+)), myeloid cells (Gr-1(+)/Mac-1(+)), erythroid cells (Ter119(+)), and B lymphocytes (CD19(+)). It is concluded that both maturing CD41(+)CD45(-) hematopoietic percursor cells and homogenic endothelial cells express Flk-1 in E10.5 AGM region. It requires further functional assay in vivo to clarify whether the hematopoietic stem cells (HSCs) and their precursors retain Flk-1 expression at this developmental stage.