Male founders are injected with ENU (N-ethyl-N-nitrosourea) and harem bred to females. The pups are genetically screened using the TILLING assay (an enzyme-based heteroduplex cleavage assay) as well as nucleotide sequencing to identify and characterize target genes possessing ENU-induced mutations. E207K mutation is generated from the codon change GAG/AAG of rat Adora2a.