Distinct megakaryocyte progenitors at the steady and platelet-demanding state show variable degrees of dependency on thrombopoietin/cMpl signaling. (A): Frequencies of CD41+LSK, megakaryocytic progenitor (MKP), megakaryocyte–erythroid progenitor (MEP), and PreMegE in cMpl-deficient (cMpl−/−) and heterozygous (cMpl+/−) mice. The means of quadlicates are shown. (B): The total number of each progenitor cell population in cMpl−/− and cMpl+/− mice at several time points after 5-FU treatment (n 5 4, each group). Abbreviations: LSK, lineage−Sca1+cKit+; MEP, megakaryocyte–erythroid progenitor; MKP, megakaryocytic progenitor; PreMegE, pre-megakaryocyte/erythrocyte progenitors.