Exon 2 was floxed and a FRT-flanked PGK-neomycin-resistance cassette was inserted within intron 2 before the 3' loxP site. The floxed exon and neomycin selection cassette were removed by cre-mediated recombination. No Class 2 IGF-1 was detected by RT-PCR of liver tissue. (J:159167)