Cloning and characterization of the chicken thyrotropin-releasing hormone receptor

We report on the cloning of the full-length complementary DNA for the chicken TRH receptor. Although the TRH receptor has been cloned from several mammalian species, this is the first report from another vertebrate class. The ligand binding pocket, which is situated in the transmembrane helices of the mouse and rat TRH receptors, is completely conserved in the chicken receptor. Pharmacological studies (receptor binding and signaling) employing several TRH analogs revealed that there are no significant differences between the chicken and mouse receptors. These findings show that there have been considerable evolutionary constraints on TRH receptor structure and function. Several truncated forms of the chicken TRH receptor that appear to retain a part of an intron and are truncated in the putative third intracellular loop were also cloned, but were nonfunctional. This study provides a useful tool for further studies on the roles of TRH in avian growth and TSH regulation.