C-MPL LIGAND IS A HUMORAL REGULATOR OF MEGAKARYOCYTOPOIESIS

MEGAKARYOCYTOPOIESIS is the cellular developmental process that leads to platelet production. At least two humoral growth factors mag be nec essary for megakaryocyte proliferation and maturation. One is a megaka ryocyte-colony stimulating factor (MK-CSF) which induces the prolifera tion and differentiation of megakaryocyte progenitors(1,2), and the se cond, thrombopoietin, is a megakaryocyte maturation factor(3). Neither of these factors has been fully characterized. The proto-oncogene c-m pl, an orphan member of the haematopoietin receptor family(4-6), is sp ecifically involved in megakaryocyte regulation(7). Here we present ev idence that the c-mpl-encoded receptor binds a ligand (c-Mpl ligand) w hich is a humoral factor implicated in platelet homeostasis. Our resul ts suggest that c-Mpl ligand, thrombopoietin and MK-CSF might be the s ame molecule.