Temporal expression and T3 induction of thyroid hormone receptors α1 and β1 during early embryonic and larval development in zebrafish, Danio rerio

Abstract

The effects of thyroid hormones on metabolism and development are mediated by thyroid hormone receptors (TRs). We report the cloning and characterization of a TRβ1 cDNA from zebrafish. Southern blot analysis revealed that there is a single genomic locus for the TRβ gene, while the TRα gene potentially has two loci. Multiple TRα and TRβ transcripts were detected in adult tissues. Using a semiquantitative RT-PCR assay, zygotic expression of TRα1 and TRβ1 were shown to occur before the midblastula transition stage. In transiently transfected HeLa cells, TRα1 displayed constitutive transactivation in the absence of ligands, which was slightly enhanced by triiodothyronine (T3). The transactivating activity of TRβ1 was strictly ligand-dependent and repressed in the absence of T3. Finally, the T3 induction of TRα1 and TRβ1 mRNAs was demonstrated in zebrafish embryos and larvae. The auto-induction of TRα1 and TRβ1 may serve a regulatory role during the embryonic and larval development of zebrafish. (C) 2000 Elsevier Science Ireland Ltd.