mRNA expression of murine c-mpl by Northern blot (A) and that of murine c-mpl ligand (thrombopoietin) by RT-PCR followed by Southern blot (B) in the M1 clonal lines stably transfected with the GATA-1 expression vector. The membrane containing 5 μg poly(A)⁺ RNA from each cell was hybridized with murine c-mpl and β-actin cDNA (A). Murine β-actin was the internal control for RT-PCR (B). Lane 1, parental M1 cells; lane 2, M1 cels transfected with control vector; lane 3, M1GATA-Y1 clone; lane 4, M1GATA-Y22 clone; lane 5, M1GATA-Y25 clone.