Dose-dependent effect of GFI1 expression in the reconstitution and the differentiation capacity of HSCs.

GFI1 is a transcriptional repressor and plays a pivotal role in regulating the differentiation of hematopoietic stem cells (HSCs) towards myeloid and lymphoid cells. Serial transplantation of deficient HSCs repopulated whole hematopoietic system but in a competitive setting involving wild-type HSCs, they lose this ability. The underlying mechanisms to this end are poorly understood. To better understand this, we used different mouse strains that express either loss of both alleles (-KO), with reduced expression of (-KD) or wild-type (-/-WT; corresponding to the mouse and human alleles). We observed that loss of or reduced expression of led to a two to four fold lower number of HSCs (defined as LinSca1c-KitCD150CD48) compared to -WT mice. To study the functional influence of different levels of GFI1 expression on HSCs function, HSCs from -WT (expressing CD45.1 + surface antigens) and HSCs from -KD or -KO (expressing CD45.2 + surface antigens) mice were sorted and co-transplanted into lethally irradiated host mice. Every 4 weeks, CD45.1+ and CD45.2 + on different lineage mature cells were analyzed by flow cytometry. At least 16 weeks later, mice were sacrificed, and the percentage of HSCs and progenitors including GMPs, CMPs and MEPs in the total bone marrow cells was calculated as well as their CD45.1 and CD45.2 expression. In the case of co-transplantation of -KD with -WT HSCs, the majority of HSCs (81% ± 6%) as well as the majority of mature cells (88% ± 10%) originated from CD45.2 + -KD HSCs. In the case of co-transplantation of -KO HSCs with -WT HSCs, the majority of HSCs originated from CD45.2+ and therefore from -KO (61% ± 20%); however, only a small fraction of progenitors and mature cells originated from -KO HSCs (<1%). We therefore in summary propose that GFI1 has a dose-dependent role in the self-renewal and differentiation of HSCs.