The expression of Mpl is not regulated by R1E. (A) Relative expression levels (REL) of Mpl transcript in cDNA from GFP(+)-sorted BM progenitors transduced with MIG, MID-PL2, or MIG-R1E, using qRT-PCR and normalized to the average of MIG sample; experiments were performed in triplicate. (B) Relative expression levels (REL) of Mpl transcript in cDNA from GFP(+)-sorted MIG-R1E/MID-PL2, MIG-R1E/MID-MPL, and MIG-R1E/MID (n = 3) leukemic cells, using qRT-PCR and normalized to MIG-R1E/MID-Pl2; experiments were performed in triplicate. (C) Epression of Mpl in cell surface of hCD4(+)- or GFP(+)-gated Lin(−) BM cells pretransduced with MID-MPL (left), MIG (middle left), and MIG-R1E (middle right) retroviruses was determined by flow cytometry, and compared with untransduced BM cells (gray shaded). Mpl ecpression in transduced cells is shown in left panel. (D) Expression of MPL in cell surface of GFP(+) MIG-R1E9a/MID (n = 2, left panels) and MIG-R1E/MID-MPL (n = 2, middle panels) leukemic cells was determined by flow cytometry, and compared with untransduced BM cells (gray shaded). Mpl expression in transduced cells is shown in left panel.