Conditional targeting of the murine Appl1 gene. A, diagram of Appl1 locus and targeting vector showing the position of probes (5′ probe and 3′ probe) used for Southern blotting. B, Southern blot analysis of ES cell DNA used to identify correctly floxed clones by using the 3′ probe. F, floxed allele. C, Southern blot analysis using the 5′ probe. D, PCR genotyping (using primers 3 and 4) of tail DNA from mouse in which neo cassette has been removed. E, PCR genotyping (using primers 1, 2, and 4) of tail DNA from mouse in which Appl1 exon 5 has been excised. Primers used in D and E correspond to sites shown in A.