In marrow transplantation models of JAK2V617F+ MPNs, Mpl and Tpo are required for aberrant hematopoiesis. (A) Platelet, (B) neutrophil counts, and (C) hematocrit from WT into WT, JAK2V617F+ into WT (VF+ into WT), Mpl−/− into Mpl−/−, JAK2V617F+Mpl−/− into Mpl−/− (VF+ into Mpl−/−), WT into Tpo−/−, and JAK2V617F+ into Tpo−/− transplant mice were monitored for 16 weeks after transplant. Data are presented as mean ± SEM; n = 2 to 10 mice per time point. (D) Plasma was collected 16 weeks after transplant from WT into WT, JAK2V617F+ into WT (VF+ into WT), Mpl−/− into Mpl−/−, JAK2V617F+Mpl−/− into Mpl−/− (VF+ into Mpl−/−), WT into Tpo−/−, and JAK2V617F+Tpo−/− mice, and TPO levels were quantified by enzyme-linked immunosorbent assay. Each data point represents a single mouse, and bars are presented as mean ± SEM; asterisks indicate significance compared with WT into WT. (E) Representative spleens and (F) weights of spleens harvested 16 weeks after transplant. Scale bar, 3 mm.