EXPRESSION OF THYROID-HORMONE RECEPTORS MESSENGER-RNAS IN RAT CEREBRAL HEMISPHERE NEURONAL CULTURES

We have studied the expression of the alpha and beta thyroid receptors mRNAs (TR-mRNAs) in cerebral hemisphere neuronal cultures, initiated from 15-day-old rat embryos, by northern analysis. In the cultures grown in the absence Of L-triiodothyronine (L-T3), the alpha2 TR-mRNAs were the predominant form of TR-mRNAs and were approximately 8 to 20-fold higher than the levels of the alpha1 TR-mRNAs, depending on the age of the cultures. The levels of alpha2 TR-mRNAs significantly increased by 1.8 fold between day 8 and 15 and remained on a plateau value thereafter until day 22. Over the same time period, there were no significant changes on the levels of alpha1 TR-mRNAs. The ratio alpha1/alpha1 + alpha2 TR-mRNAs decreased between day 8 and 15. The beta1 TR-mRNAs increased by 8 fold between day 8 and day 22. On day 8, the beta1 TR-mRNAs were 1.8 fold lower than the levels of the alpha1 TR-mRNAs while they were 6 fold higher on day 22. L-T3 treatment of the cultures had no effect on the levels of the alpha1, alpha2 and beta1 TR-mRNAs. The differential temporal expression of the alpha1 and beta1 TR-mRNAs suggests distinct functions for both types of T3 receptors in neuronal maturation.