The present invention relates to novel identified polynucleotides, polypeptides encoded by them and to the use of such- polynucleotides and polypeptides, and to their production. More particularly, the polynucleotides and polypeptides of the present invention relate to the G-protein coupled receptor family, referred to as IGS4-family. The invention also relates to inhibiting or activating the action of such polynucleotides and polypeptides, to a vector containing said polynucleotides, a host cell containing such vector and transgenic animals where the IGS4-gene is either overexpressed, misexpressed, underexpressed or suppressed (knock-out animals). The invention further relates to a method for screening compounds capable to act as an agonist or an antagonist of said G-protein coupled receptor family IGS4. The invention also relates to the identification of the cognate ligand of the IGS4 polypeptides of the invention. High affinity binding to said IGS4 polypeptides is found for the neuropeptides known as neuromedin U.