Epo, SCF, and dexamethasone are each required both for restricted and for extensive erythroid self-renewal. When Epo, SCF, or dexamethasone is individually removed from the culture during restricted self-renewal or during extensive self-renewal, proliferation is halted because of cell death, decreased proliferation, or terminal maturation. Results of 1 of 3 independent experiments is shown. *Culture was ultimately composed of mast cells.