Fig. 1. Targeting strategy and in situ hybridization for Klf4. (A) The four alleles used in the gene targeting of Klf4 are shown with predicted band sizes of restriction fragments used in Southern blot analysis. Deletion of exons 2 and 3 produces a frame shift in exon 4. Exon 1 encodes only the first amino acid of the Klf4 protein. A 400 bp fragment external to the targeting vector was used as the probe for Southern blot. White arrows depict PCR primer locations. (B) Southern blot showing the wild-type and targeted Klf4 bands. (C) PCR screening for Klf4 revealed 172 bp wild-type, 296 bp floxed and 425 bp null bands. (D,E) In situ hybridization for Klf4 in colon from postnatal day 1 mice. (D) Wild-type mice demonstrated expression of Klf4 mRNA (arrows) throughout the epithelium. (E) Klf4^–/– mice showed no expression of Klf4 mRNA, confirming the successful deletion of Klf4. E, EcoRI; X, XbaI.