Posttranscriptional regulation of oligodendroglial thyroid hormone (T3) receptor β 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 α 1, α 2 and β 1 3,5,3′‐triiodo‐L‐thyronine receptor mRNAs. In culture, we find that β 1 3,5,3′‐triiodo‐L‐thyronine receptor mRNA, but not α 1 and α 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 β 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 α 1 and α 2 were expressed in both early progenitor cells and mature oligodendrocytes. In contrast, β 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 β 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 β 1 gene.