NUCLEAR LOCALIZATION OF PARATHYMOSIN IN RAT AND HUMAN HEPATOCYTES. A LIGHT AND ULTRASTRUCTURAL STUDY

Parathymosin (ParaT) is an almost ubiquitious peptide first isolated from rat thymus, the highest concentration being in the liver. Its subcellular localization is controversial and both a cytoplasmic and a nuclear distribution have been reported. The aim of the present work was to study the intracellular localization of ParaT in rat and human livers by light immunohistochemistry and immunoelectron microscopy procedures. Both in rat and human livers immunostaining for ParaT was found in the nuclei of hepatocytes, the nucleoli and the cytoplasms being negative. The intensity of immunostaining was variable from cell to cell, but virtually all hepatocytes were positive. No immunoreactivity was found in non-parenchymal cells. Immunogold labelling confirmed these results and showed that ParaT immunoreactivity was associated with both euchromatin and heterochromatin. Our results demonstrate that ParaT is localized in the nucleus of hepatocytes and support the idea that the inactivation of the cytoplasmic enzyme phosphofructokinase-1 is not the unique function of ParaT.