Novel translational repressor (NAT-1) expression is modified by thyroid state and age in brain and liver

The technique of reverse transcriptase-polymerase chain reaction differenti al display was used to identify thyroid hormone (TH) responsive mRNAs in th e adult rat cerebral tissue. A partial cDNA (0.76 kb) was cloned and sequen ced. Comparison of the sequence to the GenBank data base showed almost 100% homology to mouse translational repressor (NAT-1) mRNA 3'-end, In a northe rn blot analysis this cDNA hybridized with a mRNA whose expression in hyper thyroid rat cerebral tissue was approximately 6-fold higher than in euthyro id rats. The time course studies showed a rapid induction of this mRNA with in 3 h following thyroxine administration. This mRNA is widely expressed in various tissues, and in hepatic tissue it is also TH responsive, To determine if TH responsiveness of this mRNA persists during aging, 25-mo nth-old aged rats were studied and the results were compared with those of 4-month-old rats. Unlike young mature rats, the TH responsiveness of NAT-1 mRNA in both the cerebral and hepatic tissue of aged rats was blunted. It i s concluded that cerebral tissue in aging rats beyond the developmental sta ges, like the hepatic tissue, is associated with altered TH responsiveness.