CD45lowc-Kithigh cells have hematopoietic properties in the mouse aorta-gonad-mesonephros region

Long-term reconstituting hematopoietic stem cells first arise from the aorta of the aorta-gonad-mesonephros (AGM) region in a mouse embryo. We have previously reported that in cultures of the dispersed AGM region, CD45lowc-Kit+ cells possess the ability to reconstitute multilineage hematopoietic cells, but investigations are needed to show that this is not a cultured artifact and to clarify when and how this population is present. Based on the expression profile of CD45 and c-Kit in freshly dissociated AGM cells from embryonic day 9.5 (E9.5) to E12.5 and aorta cells in the AGM from E13.5 to E15.5, we defined six cell populations (CD45−c-Kit−, CD45−c-Kitlow, CD45−c-Kithigh, CD45lowc-Kithigh, CD45highc-Kithigh, and CD45highc-Kitverylow). Among these six populations, CD45lowc-Kithigh cells were most able to form hematopoietic cell colonies, but their ability decreased after E11.5 and was undetectable at E13.5 and later. The CD45lowc-Kithigh cells showed multipotency in vitro. We demonstrated further enrichment of hematopoietic activity in the Hoechst dye-effluxing side population among the CD45lowc-Kithigh cells. Here, we determined that CD45lowc-Kithigh cells arise from the lateral plate mesoderm using embryonic stem cell-derived differentiation system. In conclusion, CD45lowc-Kithigh cells are the major hematopoietic cells of mouse AGM.