Expression change of Flk-2/Flt-3 on murine hematopoietic stem cells in an activating state.
OBJECTIVE
The receptor tyrosine kinase Flk-2/Flt-3 (Flt-3) represents an important molecule involved in early hematopoiesis. Murine hematopoietic stem cells (HSCs) have been shown to be negative for the expression of Flt-3. We now present clear evidence for the expression change of Flt-3(-) HSCs in an activating state, and the reversibility of Flt-3 expression by HSCs in vivo.


METHODS
Bone marrow cells isolated from Ly5.1 mice were sorted on the basis of Flt-3 expression and transplanted into lethally irradiated Ly5.2 recipients. After 24 weeks, peripheral blood was analyzed for donor contribution by flow cytometry.


RESULTS
Although long-term engraftment was predominantly detected in Flt-3(-) populations as previously described, a 6-day cultivation of Lin(-/low)c-kit(+)Sca-1(+) Flt-3(-) bone marrow cells with stem cell factor and interleukin-11 resulted in the generation of Flt-3(+) HSCs with long-term engraftment capabilities. However, the Flt-3 ligand had no significant effect on self-renewal of the Flt-3(+) HSCs. Next, to examine reversible expression of this receptor molecule, Flt-3(+) cells converted in vitro from Ly5.1 Lin(-/low)c-kit(+)Sca-1(+) Flt-3(-) bone marrow cells were isolated and transplanted into Ly5.2 primary recipients. After 24 weeks, Ly5.1 Lin(-/low) bone marrow cells were again separated into Flt-3(-) and Flt-3(+) cells and retransplanted into Ly5.2 secondary recipients. The majority of donor HSCs with long-term engraftment capabilities were detected in the Flt-3(-) populations, indicating the reversion of Flt-3(+) to Flt-3(-) HSCs.


CONCLUSIONS
These observations suggest that Flt-3 is a useful cell-surface marker of HSC activation and that this phenotypic change is reversible.
Hasumura
Mai
M
Daiichi Pharmaceutical Co. Ltd., Tochigi Research Center, 519 Shimo-Ishibashi, Ishibashi-Machi, Tochigi 329-0512, Japan.
Imada
Chiharu
C
Nawa
Katsuhiko
K
D000818:Animals; D001854:Bone Marrow Cells; D016026:Bone Marrow Transplantation; D002469:Cell Separation; D015870:Gene Expression; D006085:Graft Survival; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000032:analysis* / Q000096:biosynthesis; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis* / Q000096:biosynthesis; D051941:fms-Like Tyrosine Kinase 3
D011518:Proto-Oncogene Proteins; C497971:Flt3 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3