Methods for generating an expression-enhanced GPR22 nucleic acid, as well as substituted GPR22 nucleic acids providing for enhanced expression of the encoded GPR22 polypeptide, are provided. In practicing the subject methods, a nucleic acid encoding a mammalian GPR22 receptor polypeptide (e.g., a wild-type nucleic acid) is expression-enhanced by identifying the various codons of the coding region for the GPR22 amino acid sequence and substituting nucleotides so as to enhance expression without changing the amino acid sequence of the encoded GPR22 polypeptide. Methods, compositions, and kits using the same for screening of modulators of GPR22 are also provided.