MPL and acquired polycythemia vera: To study the role of MPL in the PV phenotype, we used a JAK2V617F transgenic mouse, which develops erythrocytosis, leukocytosis and thrombocytosis with an eventual decline in erythropoiesis associated with EMH and osteomyelofibrosis over a time course of 6–46 weeks without leukemic transformation [45].