MURINE THROMBOPOIETIN MESSENGER-RNA LEVELS ARE MODULATED BY PLATELET COUNT

The activity of the c-Mpl ligand on hematopoietic progenitors meets cr iteria expected for thrombopoietin (TPO), Bioassays have shown that bl ood TPO levels are inversely related to platelet mass. We sought to id entify the molecular basis for this regulation. To determine if TPO mR NA levels respond to platelet demand, RNA from selected organs of mice with high, normal, or low platelet counts was subjected to semiquanti tative reverse transcriptase-polymerase chain reaction, Although no di fferences in TPO mRNA levels between control and treated mice could be detected in liver or kidney, TPO-specific bands were more intense aft er 25 to 30 polymerase chain reaction cycles in marrow-derived mRNA fr om thrombocytopenic mice. The TPO-specific bands were less intense in thrombocytotic mouse marrow and spleen than control mouse marrow and s pleen after 30 cycles. These data support the hypothesis that TPO leve ls are regulated, at least in part, by modulating mRNA levels in respo nse to platelet demand. (C) 1995 by The American Society of Hematology .