Thyroid hormone receptor β is widely expressed in the brain and pituitary of the Japanese eel, Anguilla japonica

Abstract

In a previous study, we cloned the thyroid hormone receptor βB (TRβB) from a teleostean fish, the Japanese conger eel ( Conger myriaster). The gene encoding this receptor is expressed in the brain and pituitary. In this study, we cloned TRβB from the brain of the Japanese eel ( Anguilla japonica) to extend our studies into thyroid hormone function in fish. RT-PCR analysis demonstrated that the TRβB transcripts were abundant in both the brain and pituitary. The TRβB cDNA encoded a 379 amino acid protein with much higher homology to the conger eel TRβB than to other fish TRs, supporting the existence of a TRβB isoform, at least in anguilliforms. In a transiently transfected Japanese eel cell line, Hepa-E1, TRβB and its splice variants in the ligand-binding domain (TRβBL) showed thyroid hormone (TH)-dependent activation of transcription from the TH-responsive promoter. In situ hybridization studies revealed the presence of TRβB transcripts in the pars distalis of the pituitary.