The targeting construct replaced exon 4 with an EGFP, inducible cre recombinase fusion gene (EGFP/cre/ERT2) and an FRT-flanked neomycin resistance cassette. Flp-mediated recombination removed the selection cassette. The EGFP could not be detected by direct fluorescence or anti-GFP antibody staining. Expression of the EGFP/cre/ERT2 fusion protein is detected by anti-estrogen receptor antibody staining in adult retinal neurons. (J:214080)