FIG.1.

Myc expression and villin::CreER^T2-mediated recombination of the c-myc^flox allele in the small intestine. (A) Immunohistochemical analysis of c-Myc in the adult duodenum. Enlargement of the indicated box is shown in A′. (B and B′) Immunohistochemistry of N-Myc in adult duodenum. (C) Schematic representation of the villin::CreER^T2 and c-myc^flox alleles used. The c-myc^ΔORFrec allele represents the locus after Cre mediated recombination. The three c-myc exons are illustrated as boxes; regions in black indicate the open reading frame. Restriction sites are shown on top. Red ovals indicate probe used for Southern blot analysis. Arrows below each scheme indicate locations of the primers used for genotyping. (D) Southern blot analysis of villin::CreER^T2; c-myc^flox/+ mice in the small intestine 6 days (duodenum, ileum, and jejunum) and 21 days (duodenum) after the first of four consecutive tamoxifen injections. The c-myc probe hybridizes to the floxed and wild-type alleles (1,926 bp) and to the deleted c-myc^ΔORFrec allele (ΔORF^rec: 1,170 bp) in recombined cells. (E and F) Immunohistochemical analysis of c-Myc in duodenal tissue sections derived from villin::CreER^T2, c-myc^ΔORF/flox mice 21 days following the first injection of tamoxifen. Solid arrows indicate c-Myc-expressing crypts (c-myc^ΔORF/flox). Open arrows indicate c-Myc-negative crypts (c-myc^ΔORF/ORFrec).