Function of Prdm16–deficient FL and BM cells. (A) Ratio between donor (Prdm16^−/−, Prdm16^+/−, or wt FL cells) and competitor (T cell–depleted CD45.1⁺ or CD45.1⁺CD45.2⁺ B6 BM cells) cells among PB myeloid and B cells 12 weeks after transplantation of 0.5 × 10⁶ cells of each population into lethally irradiated B6.129F1 (CD45.2⁺) mice (n = 3 for wt, n = 12 for Prdm16^+/−, n = 14 for Prdm16^−/−). *P < .01, one-way analysis of variance. (B-C) Ratio between donor (Prdm16^−/−, Prdm16^+/−, or wt FL cells) and competitor (T cell–depleted CD45.1⁺ B6 BM cells) cells among PB myeloid and B cells (B) and among BM LT-HSCs, ST-HSCs, and MPPs (C) 20 weeks after transplantation as in panel A. (D-E) Competitive repopulation of 2 × 10⁶ wt or Prdm16^+/− BM cells (CD45.2⁺) with 2 × 10⁶ C57BL/6 (CD45.1⁺) BM cells in B6.129F1 recipients after 12 to 16 weeks. Data presented as donor/competitor ratio within a specific compartment in PB (D) and BM (E) (n = 6). *P < .02. TBM indicates total BM. (F-G) Shift in donor/competitor ratio within B cells (F) and myeloid cells (G) after serial transplantation of 2 × 10⁶ BM cells from primary recipients into lethally irradiated secondary B6.129F1 CD45.2⁺ recipients 12 to 14 weeks after primary transplantation. The right hand panels of panels F and G show the difference in log(donor/competitor) between primary and secondary recipients (n = 12 secondary recipients for each genotype). *P = .07 for myeloid cells. *P = .01 for B cells. Tx indicates transplantation. (H) Genomic PCR for the wt and mutant alleles in the myeloid and B cells of the spleens of recipients of CD45.2⁺Prdm16^−/− cells and CD45.1⁺CD45.2⁺ B6 competitor cells.