Zebrafish (Danio rerio) Thyroid Hormone Receptor $\alpha$1 Counteracts Retinoic Acid-induced Transcription

The present study aims to characterize a cDNA encoding zebrafish thyroid hormone receptor $\alpha{1}$ $(zTR\alpha{1)}$ in order to investigate its possible role in the early stage of embryonic development. A mobility shift assay showed that $zTR\alpha{1}$ overexpressed in COS7 cells specifically bound to thyroid hormone response element (TRE). In addition, the specific interaction of anti-rat $TR\alpha{1}$ antibodies with $zTR\alpha1$/TRE complexes demonstrated that the cDNA clone encoded zebrafish thyroid hormone receptor $\alpha{1}$. Transient cotransfection assays showed that $zTR\alpha{1}$ repressed the transcription which was induced by retinoic acid (RA), a well-characterized embryonic morphogen. These results suggest that zTRal may be involved in regulating the RA-induced gene transcription during early embryonic development.