HEMATOPOIESIS Expression of the Thrombopoietin Gene in Human Fetal and Neonatal Tissues

Thrombopoietin (TPO) regulates megakaryopoiesis and platelet production. In the adult, TPO is mainly produced by the liver and the kidneys. This study focuses on fetal and neonatal TPO mRNA expression. In 26 human fetuses and preterm neonates, samples from liver, kidney, spleen, lung, and bone marrow were extracted for total RNA. We measured platelet counts, TPO serum concentrations by enzymelinked immunosorbent assay, and TPO mRNA contents by reverse transcription/competitive polymerase chain reaction. TPO mRNA concentrations per microgram total RNA were similar in liver, spleen, and bone marrow, slightly lower in kidney, and significantly lower in lung. When related to gram tissue, TPO mRNA levels were highest in the liver. Considering the total amount of TPO mRNA produced in liver, kidney, and spleen, the liver accounted for 95.3%. No correlations between TPO mRNA expression and serum TPO concentration, blood platelet count, or gestational age were observed. In conclusion, the liver is the primary site of TPO gene expression in human fetuses and neonates. The spleen may contribute to TPO production during fetal life. Like in the adult, TPO mRNA is expressed in fetal bone marrow. r 1999 by The American Society of Hematology.