Characterisation and differential expression of two very closely related G-protein-coupled receptors, GPR139 and GPR142, in mouse tissue and during mouse development

By searching the human and mouse genomic databases we found two G-protein-coupled receptors, GPR139 and GPR142, with characteristic motifs of the rhodopsin family of receptors. The gene for GPR139 maps to chromosome 7F1 of mouse and 16p12.3 of human and that for GPR142 to 11E2 of mouse and 17q25.1 of human. We isolated GPR139 from a cDNA library of adult mouse brain and GPR142 from a cDNA library of brains from 15-day-old mouse embryos. GPR139 mRNA was predominantly expressed in specific areas of human and mouse brains, whereas GPR142 mRNA showed a more ubiquitous expression both in the brain and in various peripheral glands and organs. A 50% identity and a 67% homology at the amino-acid level between the two receptors and only 20–25% identity with other G-protein-coupled receptors established them as a new subbranch within the phylogenetic tree and hints at a common or similar ligand(s). Preliminary results suggest that the cognate ligand is present in brain extracts and is, most likely, a small peptide. GPR139 signal transduction in Chinese hamster ovary cells requires coupling to an inhibitory G-protein and is mediated by phospholipase C. Dimer formation may be necessary for proper function.