A targeting vector was designed to insert a loxP-flanked neomycin resistance (neo) cassette downstream of exon 5, and a single loxP site downstream of exon 2 of the teratocarcinoma-derived growth factor 1 (Tdgf1) gene. Cre-mediated recombination removed the neo cassette and left exons 3 through 5 floxed. (J:104418)