MPD caused by the Mib1-null microenvironment. (A,B) Reciprocal BMT. Lethally irradiated CD45.1 mice were injected intravenously with BM cells from 12-week-old CD45.2 MMTV-Cre;Mib1^+/f (left, n = 5) and MMTV-Cre;Mib1^f/f (right, n = 5) mice. Twelve weeks after transplantation, the reconstituted BM cells were analyzed by flow cytometry (A). A representative of 10 independent experiments is shown. Lethally irradiated 7- to 9-week-old CD45.2 MMTV-Cre;Mib1^+/f (left, n = 5) and MMTV-Cre;Mib1^f/f (right, n = 5) mice were injected intravenously with CD45.1 congenic BM cells. Six weeks after transplantation, the reconstituted BM cells were analyzed by flow cytometry (B). A representative of 10 independent experiments is shown. (C,D) Secondary BMT. Primary and secondary BMT were performed as schematically depicted (C) and were analyzed by flow cytometry (D). Numbers around rectangles indicate the mean plus or minus SD (n = 3). (E,F) Microenvironment-induced MPD initiation by LSK. Lethally irradiated 7- to 9-week-old CD45.2 MMTV-Cre;Mib1^+/f (WT, n = 2) and MMTV-Cre;Mib1^f/f (MT, n = 3) mice were injected intravenously with 4.0 × 10³ sorted CD45.1 congenic LSK cells (E) or 8.0 × 10⁴ MP cells (F) along with 5.0 × 10⁶ CD45.2 wild-type whole BM cells. The blood cells from each recipient mouse were analyzed by flow cytometry 3.5 weeks after transplantation.