TPO and Thrombocytopenia: Indeed, homozygous TPO or c-Mpl knockout mice exhibit a profound but not lethal thrombocytopenia.[4, 5] In vitro and in vivo experiments have shown that TPO is the most potent growth factor for megakaryocyte (MK) differentiation, acting on different developmental stages, including MK progenitors, promegakaryoblasts, and MK.