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

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.