Comparison of c-mpl transcript levels in MKs in the presence or absence of TPO, by ribonuclease protection analysis (2 μg of RNA). (A) MKs obtained in the presence of TPO (3 days) were either maintained in TPO or shifted for 24 additional hours to a medium deprived of TPO, but containing a combination of SCF, IL-6, and IL-3. For each condition, three independent MK preparations were made. (B) MKs were obtained either in the presence of TPO or in the presence of a combination of SCF, IL-6, and IL-3 (4 days). Two independent MK preparations were used for each condition. Arrows on the right indicate the position of the protected fragments.