Transplantation of iLIN28B BM into WT recipients and tissue-specific LIN28B induction. (A) Lineage⁻, c-kit⁺, Sca-1⁺, CD150⁺, and CD48⁻ long-term HSCs were purified by FACS from BM of iLIN28B mice (CD45.2) exposed to doxycycline. Long-term HSCs were cotransplanted with CD45.1 BM cells into lethally irradiated CD45.1 recipient mice. Recipient mice continued to receive doxycycline in their drinking water and were sacrificed 16–20 wk after transplantation, and myeloid progenitors in the BM were analyzed within the CD45.1 and CD45.2 fractions. Representative flow cytometry plots are shown. (B) Ratio of MEP to GMP in the CD45.1 and CD45.2 fractions in mixed chimeric recipient mice is presented. *, P < 0.0001 by Student’s t test. n = 10 mice. (C) Triple transgenic mice carrying alleles for iLIN28B, the reverse tetracycline transactivator (rtta) downstream of a loxp-flanked stop codon cassette, and Vav1-cre for hematopoietic-specific excision of the loxp-flanked stop cassette and hematopoietic-specific expression of rtta and transcription of the iLIN28B transgene in the presence of doxycycline. Exposure of triple transgenic mice to doxycycline (Dox) for 14 d resulted in robust LIN28B induction in the adult BM as assessed by Western blotting. (D and E) Myeloid progenitor profiles were assessed after 14 d of doxycycline exposure in triple transgenic mice compared with unexposed mice. *, P < 0.05 by Student’s t test. (F and G) BM cells were stained for erythroid cells, and numbers of CD71⁺/Ter119⁻ cells were quantified. *, P = 0.02 by Student’s t test. (H and I) BM cells were stained to assess granulocyte maturation, and numbers of Gr-1⁺/Mac-1⁺ cells were quantified. *, P = 0.001 by Student’s t test. (D–I) n = 3 mice across two experiments for each condition. Error bars represent SEM.