Homologous recombination in ES cells targeted to insert the fluorescent protein tdTomato, cre recombinase and the diphtheria toxin receptor (DTR) separated by P2A sequences (tdTomato-P2A-Cre-P2A-DTR) into the endogenous Zfp683 locus whereby the targeting sequence replaced exons 2, 3 and 4, as well as intronic sequences of the Zfp683 gene (knockin knockout). An FRT-flanked neomycin resistance gene was also introduced. Embryonic stem cell-derived offspring were then bred with FLPO mice to remove neo selection cassette. (J:306904)