Targeted disruption of c-Myc in the mammary gland. (a) Schematic diagram of c-myc floxed allele and recombined allele after Cre-mediated excision of floxed region. The position of the 220 base pair (bp) polymerase chain reaction (PCR) product for detecting recombined allele is indicated. (b) Immunohistochemistry against Cre (brown nuclei) on paraffin sections of mutant mammary glands. Representative staining from different stages of pregnancy (P), lactation (L), and involution (I). Scale bar, 100 μm. (c) PCR on genomic DNA from glands taken at the indicated days from wild type (WT) (W) and mutant (M) mice to detect the recombined c-myc allele (220 bp) indicated in (a). (d) Semi-quantitative reverse transcription-PCR showing c-myc and β-actin mRNA levels in glands of WT and mutant mice removed at two time points during a first pregnancy and at seven times in lactation. (e) Relative expression levels of p21
Cip1 determined by qPCR in WT and mutant glands at four different time points in lactation. Results are the average of duplicate measurements with β-actin mRNA levels as reference.