The targeting construct inserted into the locus a CAGGS promoter, loxP site, lox511 site, an inverted Rspo3 sequence, loxP site, lox511 site, polyadenylation sequence and FRT-flanked puromycin resistance cassette. Cre-mediated recombination is needed to restore correct orientation of the coding sequence under control of the upstream ubiquitous CAGGS promoter. (J:309330)