The targeting vector contains a loxP-flanked STOP cassette upstream of exon 2 and an internal ribosome entry site (IRES) fused to a green fluorescent protein (GFP) sequence inserted downstream of exon 2. The construct also contains an FRT-flanked neomycin resistance (neo) cassette. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:287989)