Differential expression of poly(ADP-ribose) polymerase and DNA polymerase beta in rat tissues

The activities of two DNA repair-related enzymes, poly(ADP-ribose) polymerase and DNA polymerase beta, and their mRNA levels were measured in 17 tissues of Wistar rats. A large variety in enzyme activity values could be detected in the tissues examined; the highest levels of activity for both enzymes were found in the testis. A good correlation between poly(ADP-ribose) polymerase activity and the level of the transcript of the gene coding for the enzyme was observed in many tissues. A less satisfactory correlation could be evidenced for DNA polymerase beta. The almost parallel amounts of the mRNAs for poly(ADP-ribose) polymerase and DNA polymerase beta in the tissues examined suggest a possible coexpression of the genes coding for these enzymes. Additional studies have been carried out in testis and liver by immunohistochemical techniques and by in situ hybridization analyses. While in the testis the spermatocytes were shown to contain both enzymes and their transcripts, in other types of cells this could not be observed. In the liver mRNAs and enzymes were only found in 20% of the hepatocytes. This may in part explain both the low levels of the mRNAs and the modest activities of the two enzymes in that tissue.