Expression of alpha and beta thyroid receptors during oligodendrocyte differentiation.

To determine which thyroid receptor (TR) isoforms are expressed during oligodendrocyte differentiation, we studied the expression of the mRNAs encoding two alpha (alpha 1 and alpha 2) and one beta (beta 1) TR isoforms in a bipotential oligodendrocyte-type 2-astrocyte (O-2A) progenitor cell line (CG-4) as well as in rat O-2A progenitor cells and oligodendrocytes. O-2A progenitor cells expressed only TR alpha-mRNAs, whereas oligodendrocytes and type 2-astrocytes also expressed TR beta 1-mRNAs. The differential expression of alpha 1 and beta 1 TRs suggests specific functions for both types of TRs during oligodendrocyte differentiation. We present evidence for a possible role of TR alpha 1 in the effect of thyroid hormones on the proliferation of CG-4 cells maintained as progenitor cells.