Posttranscriptional regulation of oligodendroglial thyroid hormone (T3) receptor beta 1 by T3

3,5,3'-triiodo-L-thyronine interacts with the genome by binding and activating nuclear 3,5,3'-triiodo-L-thyronine receptors. To determine how in secondary oligodendrocyte cultures, exogenous 3,5,3'-triiodo-L-thyronine influences the expression of different 3,5,3'-triiodo-L-thyronine receptor isoforms, we studied the regulation of alpha 1, alpha 2 and beta 1 3,5,3'-triiodo-L-thyronine receptor mRNAs. In culture, we find that beta 1, 3,5,3'-triiodo-L-thyronine receptor mRNA, but not alpha 1 and alpha 2 3,5,3'-triiodo-L-thyronine receptor mRNAs, is up-regulated by 3,5,3'-triiodo-L-thyronine in a time and dose dependent manner. In addition, we present evidence indicating that beta 1 3,5,3'-triiodo-L-thyronine receptor expression is posttranscriptionally regulated by 3,5,3'-triiodo-L-thyronine. Previous studies from our laboratory and others have shown that in the rat oligodendrocyte lineage, 3,5,3'-triiodo-L-thyronine receptors alpha 1 and alpha 2 were expressed in both early progenitor cells and mature oligodendrocytes. In contrast, beta 1 3,5,3'-triiodo-L-thyronine receptor was found to be expressed only in mature oligodendrocytes. This suggests that thyroid hormone may influence oligodendrocyte differentiation and maturation via 3,5,3'-triiodo-L-thyronine receptor beta 1, which is expressed only in oligodendrocytes and not in progenitor cells. We therefore show that this effect is indirect and is mediated by 3,5,3'-triiodo-L-thyronine which acts posttranscriptionally on the 3,5,3'-triiodo-L-thyronine receptor beta 1 gene.