Sf3b1 haploinsufficiency causes impaired competitive repopulating capacity of HSCs. (A) Contribution of donor cells to PB hematopoiesis. WT and Sf3b1^+/− BM cells (2 × 10⁶ cells, CD45.2⁺) together with an equal number of CD45.1⁺ competitor BM cells were transplanted into lethally irradiated recipient (CD45.1⁺) mice. Chimerism of donor-derived CD45.2⁺ cells in the PB is shown as mean ± SD (n = 5). (B) Chimerism of donor-derived CD45.2⁺ cells in total BM cells and LSK cells at 11 months posttransplantation shown as mean ± SD (n = 5). (C) Serial transplantation assays. WT and Sf3b1^+/− BM cells (2 × 10⁶ cells, CD45.2⁺) together with an equal number of CD45.1⁺ competitor BM cells were transplanted into lethally irradiated recipient (CD45.1⁺) mice. At 4 months posttransplantation, 2 × 10⁶ whole BM cells from the primary recipient mice were transplanted into the secondary recipient mice. Chimerism of donor-derived CD45.2⁺ cells was detected in total MNCs and myeloid cells in the PB at 4 months postprimary (1°) and -secondary (2°) transplantation and is shown as mean ± SD (n = 9). (D) Homing assays. CFSE-labeled WT and Sf3b1^+/− BM MNCs (10⁶ cells) were transplanted into lethally irradiated mice. Frequencies of CFSE⁺ cells detected in BM at 8 hours posttransplantation are shown as mean ± SD (n = 5). *P < .05; **P < .01; ***P < .001. N.S., not significant.