The Y114A mutation within the FERM domain inhibits abnormal hematopoiesis by Jak2V617F. Mice were lethally irradiated and the bone marrow was reconstituted with Jak2V617F- and Jak2V617F.Y114A-expressing fetal liver cells. (A) The hematocrit and the percentage of GFP-positive cells (GFP⁺) in peripheral blood of Jak2V617F- and Jak2V617F.Y114A-expressing mice were determined, at the times indicated. (B) Mice were killed on day 70 and the weight of the spleens was compared. (C) Spleen, peripheral blood, and bone marrow cells were used to compare the potential for colony-forming units (CFUs) or blast-forming units (BFUs), including megakaryocyte (MEG), mixed (MIX), granulocyte/erythroid/macrophage/megakaryocyte (GEMM), BFU erythroid (BFU-E) or CFU macrophage (CFU-M), CFU granulocyte/macrophage (CFU-GM), and CFU granulocyte (CFU-G). Cells were left untreated or maintained in the presence of growth factors or erythropoietin (Epo; n = 3).