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.