A 4.8 kb reporter cassette containing YFP, IRES site, humanized cre recombinase, bGH polyA, and a loxP-flanked neo selection marker was inserted at the Mcpt8 start site via homologous recombination in ES cells contain PrmCre (PC3 cells with Tg(Prm-cre)70Og). Upon crossing male chimeras to wild-type females, the loxP-flanked neo was deleted from the male germline by cre recombination, producing the final knock-in allele. (J:172122)