Generation of Fnip1 KO mice. Left schematics show Fnip1 WT (Fnip1⁺), targeted (Fnip1^lox), and gene-trapped (Fnip1^β-Geo) alleles. The Fnip1^lox mutation was introduced in the germ line by targeting a neomycin resistance cassette (flanked by LoxP sites) within intron 5, followed by a second LoxP site within intron 6. The Neo-exon 6 sequence was removed by crossing targeted mice with β-actin-Cre transgenic mice.¹⁹  Exon 6 deletion generates a premature termination codon in exon 7. Fnip1^β-Geo mice were derived from GeneTrap ES cell clone RRM154, which carries a splice acceptor (SA) β-Geo cassette inserted within intron 2. Proper gene targeting in both cases was confirmed by Southern blotting (right gel pictures).