THPO and myelofibrosis: The etiology of myelofibrosis in human subjects is poorly understood, but previous work established that BM fibrosis in mice can be induced by overexpressing ThPO from hematopoietic cells, which results in the expansion of megakaryocytes, elevated expression of platelet-derived growth factor and transforming growth factor β and the activation of mesenchymal stromal cells10,25.