A loxP site was introduced to intron 1 and a FRT-flanked neomycin cassette followed by a loxP site was placed in intron 2. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exon 2 floxed. Cre-mediated recombination removed exon 2. Immunohistochemistry of hypothalamus tissues confirmed that no protein was expressed in mutant mice. (J:238330)