Ldb1 is continuously required for erythropoiesis and megakaryopoiesis in adults. (A) Survival plot of adult MxCre ldb1^fl/fl mice (n = 8) and control ldb1^fl/fl mice (n = 6) after repeated pI:pC injection (arrows). (B) Hematocrits of MxCre ldb1^fl/fl and control ldb1^fl/fl mice after injection of pI:pC on days 1, 3, and 5. **, P < 0.01. Values are expressed as means ± SD. (C) Lin^lo/−Sca1⁻c-kit⁺FcγR^lo/−CD34^lo/− (MEP), CD71^hiTer119^lo proerythroblasts, and Ter119⁺CD71⁺ erythroblasts in BM of indicated mice after pI:pC injection. Numbers are the percentage of cells in the indicated gate. Histograms show the percentage of cycling (DAPI^int–hi) and apoptotic (annexin V⁺) Ter119⁺CD71⁺ erythroblasts. (D) H&E-stained sternum sections from pI:pC-injected MxCre ldb1^fl/fl and ldb1^fl/fl mice. Arrows indicate megakaryocytes. Bars, 50 µm. (E) Peripheral blood platelet counts on days 4 and 8 after initial pI:pC injection. **, P < 0.01. Values are expressed as means ± SD. In C and D, mice were injected with pI:pC on days 1, 3, and 5 and sacrificed on day 8. In B–E, data shown are from four MxCre ldb1^fl/fl mice and six littermate controls. Controls included ldb1^fl/fl mice and ldb1^fl+ mice ± MxCre.