Sequence for the self-cleaving A2 peptide, a diphtheria toxin receptor (HBEGF/DTR) cDNA and a loxP site flanked neomycin resistance gene cassette were inserted immediately upstream of the endogenous stop codon. The neo cassette was removed through subsequent cre-mediated recombination. This allele expresses the endogenous peptide and the inserted DTR peptide. (J:283792)