Protocol for assessing rapid effects on myelopoiesis and the starting cell population obtained. (A) The protocol used to obtain a cell population containing myeloid progenitors transduced with C/EBPα-ER or PU.1-ER(T) but lacking mature myeloid cells. Cells were split on day 0 (D0) with or without E₂ and analyzed on D2. (B) Wright-Giemsa stain of cytospun D0 cells. (C) D0 cells were analyzed by FACS for expression of the indicated surface markers. (D) CFUs arising from D0 cells plated in SCF, IL-11, IL-3, GM-CSF, Epo, and Tpo were enumerated (mean values and SE from 2 determinations with independently transduced cells are shown). (E) Percentage of transduced D0 Ly5.1 marrow cells that were monocytes (M, Mac1⁺Gr-1^–), granulocytes (G, Mac1⁺Gr-1⁺), or erythroid cells (E, Ter119⁺) 6 days after transplantation into Ly5.2 mice (cells pooled from 5 recipients). (F) Protein extracts from D0 cells or equal numbers of D0 cells cultured for 2 days in M-CSF/SCF (M2), G-CSF/SCF (G2), or IL-3/IL-6/SCF (I2) were subjected to Western blotting for endogenous C/EBPα or β-actin.