<prompt> The major regulator of platelet production is the hormone thrombopoietin THPO, which is produced byKidneysLiverLiver and kidneysSpleen and lymph nodes  <response>: Thrombopoietin THPO also known as megakaryocyte growth and development factor MGDF is a protein that in humans is encoded by the THPO gene.Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the production of platelets. It stimulates the production and differentiation of megakaryocytes, the bone marrow cells that bud off large numbers of platelets.Ref: Ganong;s review of medical physiology;24th edition; page no-80 