Figure 1  Generation of the Conditional Apc Allele
(A) Schematic diagram of exons 14 and 15 of the mouse Apc gene, the targeting vector, and the resulting conditional allele with 2 LoxP sites sandwiching the exon 14. The PGK-neomycin cassette was inserted within intron 14 by recombineering technique. This cassette is sandwiched by 2 FRT sites that could be removed by crossing to FLPe-expressing mice. Positions of PCR primers used for genotyping PCR (F2, R2, R4) and RT-PCR (F546 and R721) are indicated. Positions of probe used for Southern blot analysis with NdeI sites are also shown. Upon Cre-mediated recombination, exon 14 is removed and leads to truncated Apc protein, of which the first 580 aa correspond to the normal.
(B) Southern blot analysis of NdeI-digested genomic tail DNA isolated from F1 mice of various Apc mouse lines (ApcCKON, ApcΔ580), hybridized to a 600-bp probe. Tail genomic DNA from ApcCKON F1 mice derived from a modified ES clone showed a 12-kb band for the ApcCKON allele and a 10-kb band for the wild-type allele, whereas genomic DNA from the ApcΔ580 mouse was heterozygous for the ApcΔ580 allele (9.2-kb band).
(C) Kaplan-Meier survival plot of ApcCKO/+ mice (thin solid line, n = 39), ApcCKO/CKO mice (thin dotted line, n = 57), ApcΔ580/+ mice (solid line, n = 51), and wild-type littermates (broken line, n = 21). Heterozygosity of the ApcΔ580 allele led to a significantly shortened survival (p < 0.0001), whereas those of heterozygous and homozygous ApcCKO mice had no significant difference to that of wild-type littermates.