3 DIFFERENT THYROID-HORMONE RECEPTOR ISOFORMS ARE DETECTED IN A PURE CULTURE OF OVINE OLIGODENDROCYTES

Thyroid hormones are important for the normal development of the centr al nervous system. In humans, the period around the end of the intraut erine life and the first few months of neonatal life is critically dep endent on the presence of normal amounts of thyroid hormone. There are significant events occurring during this time; myelination is one. My elin is synthesized by oligodendrocytes. A panel of site-specific poly clonal antibodies against alpha-1 thyroid hormone receptor (TR), alpha -2 variant TR, and beta-1 TR isoforms has been employed to investigate the presence of TR isoforms in a pure culture of ovine oligodendrocyt es by the avidin-biotin peroxidase immunocytochemical method. Strong n uclear staining was obtained with all the anti-TR antibodies; no react ion products were detected in the cytoplasm or cellular processes. By contrast, an anti-myelin basic protein antibody gave strong cytoplasmi c and process staining; no nuclear staining was seen. These latter res ults served to 1) confirm that the cells under study are oligodendrocy tes; and 2) prove that the nuclear staining with anti-TR antibodies is specific. Preimmune sera were totally negative. Scatchard analysis of [I-125] T3 binding by isolated oligodendrocyte nuclei demonstrated th e existence of high-affinity-low-capacity T3 binding sites with a K-a of approximate to 6 x 10(-9) M and a maximal binding capacity of appro ximate to 20 fmol/100 mu g of DNA. Our results demonstrate that differ entiated oligodendrocytes express alpha-1 and (alpha-2 variant and bet a-1 isoforms of TR at the protein level and support the notion of a di rect impact of thyroid hormones on oligodendrocytes in their regulatio n of myelin synthesis. (C) 1995 Wiley-Liss, Inc.