Sin3B is required for the competitive repopulation capacity of HSCs. (A) Schematic for serial competitive repopulation assay. Test CD45.2 bone marrow (control or Sin3B^CKO) was competed at a 1:1 ratio against wild-type CD45.1 bone marrow and injected intravenously into a lethally irradiated (12 Gy) host. Recipient animals were euthanized after 20 weeks for analysis, and 2 × 10⁶ bone marrow cells were serially transplanted into secondary recipients. Secondary recipients were euthanized after 20 weeks and 2 × 10⁶ bone marrow cells were serially transplanted into tertiary recipients. (B) Quantification of donor-derived (CD45.2) cells in the peripheral blood of recipient animals at indicated time points; n = 8. Quantification of donor-derived (CD45.2) cells of B (B220⁺) cells (C), T (CD4⁺ or CD8⁺) cells (D), and myeloid (CD11b⁺) cells (E) in the peripheral blood of recipient animals; n = 8. (F) Percent of CD45.2 cells in the bone marrow 16 hours after injection of 2 × 10⁶ lineage depleted bone marrow cells into irradiated CD45.1 mice; n = 5. (G) Representative FACS plot of donor-derived (CD45.2) HSPC populations. (H) Donor contribution of indicated cell populations in the bone marrow 20 weeks after transplantation of primary recipient animals. (I) Donor-derived B (B220⁺), T (CD4⁺ or CD8⁺), and myeloid (CD11b⁺) cells in the peripheral blood of secondary recipient (left) and tertiary recipient (right) animals; n = 4. (J) Donor contribution of indicated cell populations in the bone marrow 20 weeks after transplantation of tertiary recipient animals; n = 4. Data are represented as mean ± SEM. *P < .05; **P < .01.