In contrast, ectopic EPO expression in murine marrow cells [26] or erythroid progenitor cell-specific expression of JAK2V617F caused erythrocytosis without significant extramedullary hematopoiesis (EMH) and failed to propagate the erythrocytosis phenotype in secondary recipients [10], emphasizing the primary role of HSC, MPL and THPO in MPN pathophysiology. The gene discussed is EPO; the disease is myeloproliferative disorder.