A targeting vector is designed with (from 5' to 3') a ubiquitously expressed CAG promoter, a loxP-flanked stop cassette, a Venus reporter sequence, 3F2A (three tandem repeats of foot-and-mouth disease 2A peptide sequence) that mediates ribosomal skipping, the sidekick cell adhesion molecule 1 (Sdk1) gene sequence, a WPRE sequence, and an FRT-flanked neomycin resistance (neo) cassette. Flp-mediated recombination removed the neo cassette. (J:341917)