Structural and functional organization of the gene encoding the human thyrotropin-releasing hormone receptor

The thyrotropin-releasing hormone (TRH) receptor (TRHR) is widely distribut ed throughout the central and peripheral nervous systems. In addition to it s role in controlling the synthesis and secretion of thyroid-stimulating ho rmone and prolactin from the anterior pituitary, TRH is believed to act as a neurotransmitter as well as a neuromodulator. We have isolated genomic la mbda and P1-derived artificial chromosome clones encoding the human TRHR. T he gene was found to be 35 kb with three exons and two introns. A 541-bp in tron 1 (-629 to -89 relative to the translation start site) is conserved be tween human and mouse. A large intron 2 of 31 kb disrupts the open reading frame (starting in position +790) in the sequence encoding the supposed jun ction between the third intracellular loop and the putative sixth transmemb rane domain. A similar intron was found in chimpanzee and sheep but not in rat and mouse. Promoter analysis of upstream regions demonstrated cell type -specific reporter activation, and sequencing of 2.5 kb of the promoter rev ealed putative cis-acting regulatory elements for several transcription fac tors that may contribute to the regulation of the TRHR gene expression. Fun ctional analysis of potential response elements for the anterior pituitary- specific transcription factor Pit-1 revealed cell type-specific binding tha t was competed out with a Pit-1 response element from the GH gene promoter.