Assignment of the melatonin-related receptor to human chromosome X (GPR50) and mouse chromosome X (Gpr50)

Recent efforts to clone further members of the melatonin receptor family have led to the identification of a novel G-protein-coupled receptor in human pituitary. This receptor, referred to as H9, is clearly related to high-affinity melatonin receptors yet unable to bind this hormone. We now report the cloning and expression of the cDNA encoding the H9 receptor in mice. The mouse clone encodes a protein of 591 amino acids that shares 74% amino acid identity with the human receptor and is unable to bind 2-[125I]iodomelatonin when transiently expressed in COS-7 cells. We also determined the chromosome loci of the human and mouse H9 receptor genes. Both genes were found to be X-linked: radiation hybrid mapping revealed that the human H9 gene (GPR50) is localized to Xq28. The mouse gene (Gpr50) was determined to lie in the proximal portion of chromosome X by means of interspecific backcross analysis. These loci might be relevant to genetically based neuroendocrine disorders.