S. Nomura et al., CELLULAR-LOCALIZATION OF THROMBOPOIETIN MESSENGER-RNA IN THE LIVER BYIN-SITU HYBRIDIZATION, Experimental hematology, 25(7), 1997, pp. 565-572
The expression of thrombopoietin (TPO) mRNA is observed in several tis
sues, including liver, kidney, brain, skeletal muscle, intestine, sple
en, and bone marrow. Among these organs, the highest expression of TPO
mRNA is detected in the liver. We identified cells producing TPO by m
eans of in situ hybridization of adult rat liver using digoxigenin-11-
UTP-labeled cRNA probes. We found that the cells expressing TPO mRNA a
lso expressed serum albumin mRNA. TPO mRNA was detected in parenchymal
cells (hepatocytes) but not in non-parenchymal cells (including endot
helial cells, epithelial cells, and so forth). To determine the locati
on of TPO expression in embryogenesis, sections of fetal mice were fur
ther analyzed by in situ hybridization. TPO mRNA was detected only in
hepatocytes of fetal liver, which was also the major site of hematopoi
esis. The expression of TPO mRNA in fetal liver was observed from 12.5
days post-coitus. Northern blot analysis showed that mouse liver tran
scribed the same size of TPO mRNA in the fetus and in the adult. These
results clearly demonstrate that hepatocytes are the primary site of
TPO production in the liver from fetus to adult.