TPO signaling in CB-MKs and PB-MKs. (A) Schematic representation of the major TPO-signaling pathways in MKs.^25,38  (B) After 14-16 hours of starvation, MKs were stimulated with different concentrations of TPO (10-100 ng/mL) for 20 minutes, and TPO-induced protein phosphorylation was determined. At all TPO concentrations, JAK2, S6K, and 4E-BP-1 phosphorylation was significantly stronger in CB-MKs compared with PB-MKs. (C) After the same overnight starvation, MKs were stimulated with 50 ng/mL TPO for different time periods (10, 20, and 40 minutes). At all time points, JAK2, S6K, and 4E-BP-1 phosphorylation was stronger in CB-MKs compared with PB-MKs. The images shown are representative of 3 separate time courses and 2 dose-response experiments.