Activin A, BMP2, and BMP4, 3 members of the transforming growth factorfamily, are involved in the regulation of hematopoiesis. Here, we explored the role of these molecules in human megakaryopoiesis using an in vitro serum-free assay. Our results highlight for the first time that, in the absence of thrombopoietin, BMP4 is able to induce CD34 progenitor differentiation into megakaryocytes throug...

Activin A, BMP2, and BMP4, 3 members of the transforming growth factor-beta family, are involved in the regulation of hematopoiesis. Here, we explored the role of these molecules in human megakaryopoiesis using an in vitro serum-free assay. Our results highlight for the first time that, in the absence of thrombopoietin, BMP4 is able to induce CD34(+) progenitor differentiation into megakaryocyt...

In this issue of Blood, Liu et al show that response to thrombopoietin receptor agonist (TPO-RA) therapy in immune thrombocytopenia (ITP) is associated with restoration of monocyte Fcg receptor (FcgR) balance toward inhibitory FcgRIIb and with correction of the enhanced phagocytic capacity of macrophages. These data suggest that TPO-RA can increase platelet counts not only by increasing platele...

Thrombopoietin (also called c-Mpl ligand, megakaryocyte growth and development factor, megapoietin) has recently been purified and cloned. This molecule is indeed the long-sought-after hematopoietic factor that controls platelet production. Thrombopoietin levels increase within 24 h after the onset of thrombocytopenia and are inversely and exponentially proportional to the platelet count. Injec...

The thrombopoietin receptor (TpoR) is a type I transmembrane protein that mediates the signaling functions of thrombopoietin (Tpo) in regulating megakaryocyte differentiation, platelet formation, and hematopoietic stem cell renewal. We probed the role of each of the four extracellular domain putative N-glycosylation sites for cell surface localization and function of the receptor. Single N-glyc...