piggyBac transposase mediated recombination inserted the ZG-s transposable gene-trap vector into intron 2. The gene-trap vector consists of piggyBac terminal repeats and internal sequence with all potential splice donor sites removed flanking a loxP site, a splice acceptor site, an IRES-beta-galactosidase-polyA cassette, an FRT site, a CAG-eGFP-polyA cassette, a loxP site, a lox5171 site, and an FRT site. Flp-mediated recombination removes the eGFP cassette. Cre-mediated recombination removes the splice acceptor and beta-galactosidase cassette restoring gene expression.