An EGFPcre sequence was inserted into exon 1, replacing the endogenous ATG with the translational start site of the EGFPcre, yet preserving the last 10 bp of the splice-donor site of exon 1. A FRT flanked neo was inserted downstream to replace parts of exon 2 and exons 3-8. Transient FLP expression excised the neo. Southern blot and multiplex PCR confirmed recombination in hemizygous mice. Immunoblot of FLCs demonstrated green fluorescence in hemizygous and homozygous embryos, with homozygotes showing a 2-fold increase in fluorescence intensity compared to hemizygotes.