Soluble thrombopoietin receptor (Mpl) and granulocyte colony-stimulating factor receptor directly stimulate proliferation of primitive hematopoietic progenitors of mice in synergy with steel factor or the ligand for flt3/flk2 - Ku, H; Hirayama, F; Kato, T; Miyazaki, H; Aritomi, M; Ota, Y; D’Andrea, AD; Lyman, SD; Ogawa, M (Blood, 1996)