JAK2 and Thrombocytopenia: As shown previously [28], upon complete deletion of Mpl, Jak2-V617F expression did not increase platelet numbers: Mpl−/−;Jak2V617F/+ mice displayed thrombocytopenia and low numbers of Mk and MkP typical of Mpl−/− mice (Fig. 6A–C, Supplementary Fig. 5A).